2023 |
Gutiérrez-Quintanilla, A., Chevalier, M., Platakyte, R., Ceponkus, J., & Crépin, C. (2023). Revisiting Photoisomerization in Fluorinated Analogues of Acetylacetone Trapped in Cryogenic Matrices. EPJD, 77, 158.
Résumé: UV-induced processes are commonly studied in acetylacetone analogues. In this contribution,
we revisit the existing work on the photoisomerization process in some of the fluorinated analogues of
acetylacetone, i.e., trifluoroacetylacetone (F3-acac) and hexafluoroacetylacetone (F6-acac). We performed
selective UV laser excitation of these molecules trapped in soft cryogenic matrices, namely neon and parahydrogen,
and probed by vibrational spectroscopy. Clear spectroscopy of 3 isomers of F6-acac and 6 isomers
of F3-acac is obtained, including the first characterization of a second open enol isomer of hexafluoroacetylacetone.
In addition, we present the electronic absorption spectra of both molecules in cryogenic matrices
before and after specific UV irradiations, giving new data on the electronic transitions of photoproducts.
Vibrational and electronic experimental results are analyzed and discussed within comparisons with DFT
and TD-DFT calculations. Our findings contribute to a deeper understanding of the photoisomerization
process in these molecules after electronic excitation in gas and condensed phase.
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Pollet, R., & Chin, W. (2023). In silico Investigation of the Thermochemistry and Photoactivity of Pyruvic Acid in an Aqueous Solution of NaCl. Chem. Eur. J., 2922(5555).
Résumé: Abstract The photochemistry of oxocarboxylic acids contributes significantly to the complex chemistry occurring in the atmosphere. In this regard, pyruvic acid undergoes photoreactions that lead to many diverse products. The presence of sodium cation near pyruvic acid in an aqueous solution, or its conjugate base in non-acidic conditions, influences the hydration equilibrium and the photosensitivity to UV-visible light of the oxocarboxylic acid. We performed an ab?initio metadynamics simulation which serves two purposes: first, it unveils the mechanisms of the reversible hydration reaction between the keto and the diol forms, with a free-energy difference of only 2?kJ/mol at 300?K, which shows the influence of sodium on the keto/diol ratio; second, it provides solvent-shared ion pairing (SSIP) and contact ion pairing (CIP) structures, including Na+ coordinated to carbonyl, for the calculations of the electronic transition energies to an antibonding π* orbital, which sheds light on the photoactivity of these two forms in the actinic region.
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2022 |
Raphaël Thon, Wutharath Chin, Didier Chamma, Mindaugas Jonusas, Jean-Pierre Galaup, & Claudine Crépin. (2022). Vibrational dynamics of iron pentacarbonyl in cryogenic matrices. J Chem Phys, 156(2), 024301-12.
Résumé: Iron pentacarbonyl is a textbook example of fluxionality. We trap the molecule in cryogenic matrices to study the vibrational dynamics of
CO stretching modes involved in the fluxional rearrangement. The infrared spectrum in Ar and N2 is composed of about ten narrow bands
in the spectral range of interest, indicating the population of various lattice sites and a lowering of the molecular symmetry in the trapping
sites. The vibrational dynamics is explored by means of infrared stimulated photon echoes at the femtosecond scale. Vibrational dephasing
and population relaxation times are obtained. The non-linear signals exhibit strong oscillations useful to disentangle the site composition
of the absorption spectrum. The population relaxation involves at least two characteristic times. An evolution of the photon echo signals
with the waiting time is observed. The behavior of all the signals can be reproduced within a simple model that describes the population
relaxation occurring in two steps: relaxation of v = 1 (population time T1 < 100 ps) and return to v = 0 (recovery time > 1 ns). These two steps
explain the evolution of the oscillations with the waiting time in the photon echo signals. These results discard fluxional rearrangement on
the time scale of hundreds of ps in our samples. Dephasing times are of the same order of magnitude as T1: dephasing processes due to the
matrix environment are rather inefficient. The photon echo experiments also reveal that intermolecular resonant vibrational energy transfers
between guest molecules occur at the hundreds of ps time scale in concentrated samples (guest/host > 104).
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Szczepaniak, U., Kolos, R., Guillemin, J. - C., & Crépin, C. (2022). Phosphorescence of C5N– in rare gas solids. Photochem, 2, 263–271.
Résumé: Phosphorescence of C5N– was discovered following the ArF-laser (193 nm) photolysis of cy-anodiacetylene (HC5N) isolated in cryogenic argon, krypton and xenon matrices. This visible emission, with the origin around 460 nm, is vibrationally resolved, permitting the measurement of frequencies for eight ground-state fundamental vibrational modes, including the three known from previous IR absorption studies. Phosphorescence lifetime amounts to tens or even hun-dreds of ms depending on the matrix host; it is 5 times longer than in the case of HC5N.
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2021 |
Gutiérrez-Quintanilla, A., Platakyte, R., Chevalier, M., Crépin, C., & Ceponkus J. (2021). Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy. J Phys Chem A, 125, 2249–2266.
Résumé: Enol forms of trifluoroacetylacetone (TFacac) isolated in molecular and rare gas matrices were studied using infrared (IR) and Raman spectroscopy. Additionally, calculations using DFT B3LYP and M06-2X as well as MP2 methods were performed in order to investigate the possibility of coexistence of more than one stable enol form isomer of TFacac. Calculations predict that both stable enol isomers of TFacac, 1,1,1-trifluoro-4-hydroxy-3-penten-2-one (1) and 5,5,5-trifluoro-4-hydroxy-3-penten-2-one (2), could coexist, especially in matrices where the room temperature population is frozen, 1 being the most stable one. Raman and IR spectra of TFacac isolated in nitrogen (N2) and carbon monoxide (CO) matrices exhibit clear absorption bands, which cannot be attributed to this single isomer. Their relative band positions and intensity profiles match well with the theoretical calculations of 2. This allows us to confirm that in N2 and CO matrices both isomers exist in similar amounts. Careful examination of the spectra of TFacac in argon, xenon, neon, normal, and para-hydrogen (Ar, Xe, Ne, nH2, and pH2 respectively) matrices revealed that both isomers coexist in all the explored matrices, whereas 2 was not considered in the previous spectroscopic works. The amount of the second isomer (2) in the as-deposited samples depends on the host. The analysis of TFacac spectra in the different hosts and under various experimental conditions allows the vibrational characterization of both chelated isomers. The comparison with theoretical predictions is also investigated.
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Pollet R, & Chin, W. (2021). Reversible Hydration of alpha-Dicarbonyl Compounds from Ab Initio Metadynamics Simulations: Comparison between Pyruvic and Glyoxylic Acids in Aqueous Solutions. J Phys Chem B, 125(11), 2942.
Résumé: Glyoxylic and pyruvic oxoacids are widely available in the atmosphere as gas-phase clusters and particles or in wet aerosols. In aqueous conditions, they undergo interconversion between the unhydrated oxo and gem-diol forms, where two hydroxyl groups replace the carbonyl group. We here examine the hydration equilibrium of glyoxylic and pyruvic acids with first-principles simulations in water at ambient conditions using ab initio metadynamics to reconstruct the corresponding free-energy landscapes. The main results are as follows: (i) our simulations reveal the high conformational diversity of these species in aqueous solutions. (ii) We show that gem-diol is strongly favored in water compared to its oxo counterpart by 29 and 16 kJ/mol for glyoxylic and pyruvic acids, respectively. (iii) From our atomic-scale simulations, we present new insights into the reaction mechanisms with a special focus on hydrogen-bond arrangements and the electronic structure of the transition state.
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2020 |
Gutierrez-Quintanilla, A., Chevalier M, Platakyte, R., Ceponkus J, & Crepin, C. (2020). Intramolecular hydrogen tunneling in 2-chloromalonaldehyde trapped in solid para-hydrogen. Phys Chem Chem Phys, 20, 28658–28666.
Résumé: The internal dynamics of a 2-chloromalonaldehyde (2-ClMA) molecule, possessing a strong internal hydrogen bond (IHB), was examined by means of matrix isolation spectroscopy in a soft host: para-hydrogen (pH2). 2-ClMA is a chlorinated derivative of malonaldehyde (MA), a model molecule in hydrogen transfer studies, better suited to low temperature experiments than its parent molecule. The infrared absorption spectra of 2-ClMA isolated in pH2 exhibit temperature dependent structures which are explained as transitions occurring from split vibrational levels induced by hydrogen tunneling. The doublet components associated with higher and lower energy levels are changing reversibly with the increase/decrease of the matrix temperature. The ground state splitting is measured to be 7.9 +/- 0.1 cm(-1). The presence of oH2 impurities in the pH2 matrix close to the neighborhood of the 2-ClMA molecule is found to quench the H tunneling. The data provide a powerful insight into the dynamical picture of intramolecular hydrogen tunneling in a molecule embedded in a very weakly perturbing environment.
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Strom, A. I., Gutierrez-Quintanilla A, Chevalier, M., Ceponkus J, Crepin, C., & Anderson DT. (2020). Matrix Isolation Spectroscopy and Nuclear Spin Conversion of Propyne Suspended in Solid Parahydrogen. J Phys Chem A, 124(22), 4471–4483.
Résumé: Parahydrogen (pH2) quantum solids are excellent matrix isolation hosts for studying the rovibrational dynamics and nuclear spin conversion (NSC) kinetics of molecules containing indistinguishable nuclei with nonzero spin. The relatively slow NSC kinetics of propyne (CH3CCH) isolated in solid pH2 is employed as a tool to assign the rovibrational spectrum of propyne in the 600-7000 cm(-1) region. Detailed analyses of a variety of parallel (DeltaK = 0) and perpendicular (DeltaK=+/-1) bands of propyne indicate that the end-over-end rotation of propyne is quenched, but K rotation of the methyl group around the C3 symmetry axis still persists. However, this single-axis K rotation is significantly hindered for propyne trapped in solid pH2 such that the energies of the K rotational states do not obey simple energy-level expressions. The NSC kinetics of propyne follows first-order reversible kinetics with a 287(7) min effective time constant at 1.7 K. Intensity-intensity correlation plots are used to determine the relative line strengths of individual ortho- and para-propyne rovibrational transitions, enabling an independent estimation of the ground vibrational state effective A'' constant of propyne.
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Szczepaniak, U., Gutiérrez-Quintanilla, A., Crépin, C., Guillemin, J. - C., Turowski, M., Custer, T., & Kołos, R. (2020). Spectroscopy of methylcyanodiacetylene revisited. Solid parahydrogen and solid neon matrix studies. Journal of Molecular Structure, 1218, 128437.
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Szczepaniak, U., Ozaki, K., Tanaka, K., Ohnishi, Y., Wada, Y., Guillemin, J. - C., Crépin, C., Kołos, R., Morisawa, Y., Suzuki, H., & Wakabayashi, T. (2020). Phosphorescence excitation mapping and vibrational spectroscopy of HC9N and HC11N cyanopolyynes in organic solvents. Journal of Molecular Structure, 1214, 128201.
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2019 |
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Crépin-Gilbert, C., & Savchenko, E. (2019). Nanostructures and impurity centers in cryogenic environment. Low Temperature Physics, 45(6), 581–582.
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de Pujo, P., Ryan, M., Crépin, C., Mestdagh, J. M., & McCaffrey, J. G. (2019). The role of spin-orbit coupling in the optical spectroscopy of atomic sodium isolated in solid xenon. Low Temperature Physics, 45(7), 715–720.
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Gutiérrez-Quintanilla A., Chevalier M., Platakyte R., Ceponkus J., & Crépin C. (2019). Selective photoisomerisation of 2- chloromalonaldehyde. J Chem Phys, 150, 034305.
Résumé: Isomerization of 2-chloromalonaldehyde (2-ClMA) is explored giving access to new experimental data on this derivative of malonaldehyde,
not yet studied much. Experiments were performed isolating 2-ClMA in argon, neon, and para-hydrogen matrices.
UV irradiation of the matrix samples induced isomerization to three open enolic forms including two previously observed along
with the closed enolic form after deposition. IR spectra of these specific conformers were recorded, and a clear assignment
of the observed bands was obtained with the assistance of theoretical calculations. UV spectra of the samples were measured,
showing a blue shift of the absorption with the opening of the internal hydrogen bond of the most stable
enol form. Specific sequences of UV irradiation at different wavelengths allowed us to obtain samples containing only one
enol conformer. The formation of conformers is discussed. The observed selectivity of the process among the enol forms is
analyzed.
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Gutiérrez-Quintanilla,, Briant,, Mengesha,, Gaveau, M. - A., Mestdagh,, Soep,, & Poisson,. (2019). Propyne-water complexes hosted in helium droplets. Low Temperature Physics, 45(6), 634–638.
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Platakyte, R., Gutiérrez-Quintanilla, A., Sablinskas, V., & Ceponkus, J. (2019). Influence of environment and association with water, to internal structure of trifluoroacetylacetone. Matrix isolation FTIR study. Low Temperature Physics, 45(6), 615–626.
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Rojas-Lorenzo,, Lara-Moreno,, Gutierrez-Quintanilla,, Chevalier,, & Crépin,. (2019). Theoretical study of “trapping sites” in cryogenic rare gas solids doped with β-dicarbonyl molecules. Low Temperature Physics, 45, 363–370.
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2018 |
Gutierrez-Quintanilla, A., Briant M, Mengesha, E., Gaveau MA, Mestdagh, J. - M., Soep B, Crepin, C., & Poisson L. (2018). A HElium NanoDroplet Isolation (HENDI) investigation of the weak hydrogen bonding in the propyne dimer (CH3CCH)2. Phys Chem Chem Phys, 20, 28658.
Résumé: A HElium Nanodroplet Isolation (HENDI) experiment was performed to explore the absorption spectra of the propyne monomer (CH3CCH), dimer and (CH3CCH)>/=3 multimers in the vicinity of the CH stretch region nu1 of the monomer. Ab initio calculations were performed at the MP2 level to document the potential energy surface of the dimer. This provided the necessary parameters to simulate the absorption spectrum of the dimer and thus facilitate the interpretation of the experiment. The central result was to observe three isomers of the dimer, hence reflecting the complexity of the weak CHpi H-bonding when several H-donors are at play.
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Gutierrez-Quintanilla, A., Chevalier M, Ceponkus, J., Lozada-Garcia RR, Mestdagh, J. - M., & Crepin C. (2018). Large amplitude motions within molecules trapped in solid parahydrogen. Faraday Discuss, 212, 499–515.
Résumé: Molecules of the beta-diketone and beta-dialdehyde families were trapped in solid parahydrogen (pH2) to investigate the vibrational behavior of systems containing an intramolecular hydrogen bond (IHB). In the simplest beta-diketone, acetylacetone (AcAc), H transfer related to the IHB is coupled with methyl torsions. In pH2, the study of nuclear spin conversion (NSC) in methyl groups allows the characterisation of the influence of these large amplitude motions on the vibrational modes. The deuteration of the OH group involved in the IHB has important consequences on the vibrational spectrum of the molecule and evidence of NSC in methyl groups is difficult to obtain. In the chlorine derivative (3-chloroacetylacetone), the H-transfer is no longer coupled with methyl torsion, and NSC has undetectable effects on the IR spectrum. A search of H tunnelling splitting in the IR spectra of beta-dialdehydes trapped in pH2 was performed. A few modes of 2-chloromalonaldehyde appear as doublets and were assigned to tunnelling levels. The spectroscopic results related to large amplitude motions are detailed and discussed, highlighting puzzling effects.
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Gutierrez-Quintanilla, A., Chevalier M, Platakyte, R., Ceponkus J, Rojas-Lorenzo, G. A., & Crepin C. (2018). 2-Chloromalonaldehyde, a model system of resonance-assisted hydrogen bonding: vibrational investigation. Phys Chem Chem Phys, 20, 12888.
Résumé: The chelated enol isomer of 2-chloromalonaldehyde (2-ClMA) is experimentally characterized for the first time by IR and Raman spectroscopies. The spectra are obtained by trapping the molecule in cryogenic matrices and analyzed with the assistance of theoretical calculations. Experiments were performed in argon, neon and para-hydrogen matrices. The results highlight puzzling matrix effects, beyond site effects, which are interpreted as due to a tunneling splitting of the vibrational levels related to the proton transfer along the internal hydrogen bond (IHB). 2-ClMA is thus one of the very few molecules in which the H tunneling has been observed in cryogenic matrices. The comparison with its parent molecule (malonaldehyde) shows experimentally and theoretically the weakening of the IHB upon chlorination, with a reduced cooperative effect in the resonance assisted hydrogen bond. In addition, the Cl substitution induces an important stabilization of two open enol conformers. These two open forms appear in the spectra of as-deposited samples, meaning that, in contrast with other well-studied molecules of the same family (beta-dialdehydes and beta-diketones), they are present in the gas phase at room temperature.
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Szczepaniak, U., Kolos R, Gronowski, M., Chevalier M, Guillemin, J. - C., & Crepin C. (2018). Synthesis and Electronic Phosphorescence of Dicyanooctatetrayne (NC10N) in Cryogenic Matrixes. J Phys Chem A, 122(25), 5580–5588.
Résumé: The rodlike 1,8-dicyano-octa-1,3,5,7-tetrayne (NC10N) molecule was synthesized with UV-assisted coupling of rare-gas matrix-isolated cyanobutadiyne (HC5N) molecules. Detection of NC10N molecule was possible due to its strong orange-red (origin at 618 nm) electronic luminescence. Excitation spectra of this emission (a (3)Sigmau(+)-X (1)Sigmag(+) phosphorescence) gave access to studying the fully allowed H (1)Sigmau(+)-X (1)Sigmag(+) UV system of NC10N. The identification of observed spectral features was assisted with quantum chemical computations. Certain regularities shaping the electronic spectroscopy of NC2 nN molecules have been discussed.
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Szczepaniak, U., Kołos, R., Gronowski, M., Guillemin, J. - C., & Crépin, C. (2018). Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene. The Journal of Physical Chemistry A, 122(1), 89–99.
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2017 |
Szczepaniak, U., Kolos, R., Gronowski, M., Chevalier, M., Guillemin JC., Turowski M., Custer, T., & Crépin, C. (2017). Cryogenic Photochemical Synthesis and Electronic Spectroscopy of Cyanotetracetylene. JOURNAL OF PHYSICAL CHEMISTRY A, 121(39), 7374–7384.
Résumé: HC9N is a molecule of astrochemical interest. In this study, it was produced in cryogenic Ar and Kr matrices from UV-photolyzed diacetylene/cyanodiacetylene mixtures. Its strong phosphorescence was discovered and served for the identification of the compound. Vibrationally resolved phosphorescence excitation spectra gave insight into excited singlet electronic states. Two electronic systems were observed around 26 00034 000 cm(-1) and 35 000-50 000 cm(-1). Energies of the second excited singlet and the lowest triplet state were derived from analysis of these systems. Vibrational and electronic spectroscopic features were assigned with the assistance of density functional theory calculations. Some trends concerning the electronic spectroscopy of HC2+1N family molecules are presented.
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Thon, R., Chin, W., Chamma, D., Gutiérrez-Quintanilla, A., Chevalier, M., Galaup, J. - P., & Crépin, C. (2017). W(CO) 6 in cryogenic solids: A comparative study of vibrational properties. Journal of Luminescence, 191, 78–86.
Résumé: A comparative study of the vibrational properties of W(CO)6 has been performed in different solids at cryogenic temperatures focusing on the IR absorption and the vibrational dynamics of the CO stretching mode of the organometallic compound. Guest-host interactions are investigated in doped solids through the linear IR spectroscopy and four-wave mixing techniques at different temperatures. We show how the host nature, the trapping site, the crystallographic ordering affect the properties of the guest molecule and in particular its vibrational dynamics.
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2016 |
Gutierrez-Quintanilla, A., Chevalier, M., & Crepin, C. (2016). Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process. Phys Chem Chem Phys, 18(30), 20713–20725.
Résumé: The effect of deuteration of acetylacetone (C5O2H8) is explored by means of IR spectroscopy of its single and double deuterated isotopologues trapped in neon matrices. The whole vibrational spectra of chelated enols are very sensitive to the H-D exchange of the hydrogen atom involved in the internal hydrogen bond. UV excitation of double deuterated acetylacetone isolated in neon matrices induces the formation of four open enol isomers which can be divided into two groups of two conformers, depending on their formation kinetics. Within each group, one conformer is more stable than the other: slow conformer interconversion due to a tunneling process is observed in the dark at low temperature. Moreover, IR laser irradiation at the OD stretching overtone frequency is used to induce interconversion either from the most stable to the less stable conformer or the opposite, depending on the excitation wavelength. The interconversion process is of great help to assign conformers which are definitively identified by comparison between experimental and calculated IR spectra. Kinetic constants of the tunneling process at play are theoretically estimated and agree perfectly with experiments, including previous experiments with the totally hydrogenated acetylacetone.
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Lamarre, N., Gans, B., Vieira Mendes L.A., Gronowski, M., Guillemin, J. - C., de Oliveira N., Douin, S., Chevalier, M., Crépin, C., Kolos, R., & Boyé-Péronne, S. (2016). Excited electronic structure of methylcyanoacetylene probed by VUV Fourier-transform absorption spectroscopy. JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, 182, 286–295.
Résumé: High resolution photoabsorption spectrum of gas-phase methylcyanoacetylene (CH3C N) has been recorded from 44 500 to 130 000 cm-1 at room temperature with a vacuum ultraviolet Fourier-transform spectrometer on the DESIRS synchrotron beamline (SOLEIL). The absolute photoabsorption cross section in this range is reported for the first time. Valence shell transitions and Rydberg series converging to the ground state X+ 2E of the cation as well as series converging to electronically excited states (A+ 2 A1 and C+) are observed and assigned. Time-dependent density-functional-theory calculations have been performed to support the assignment of the experimental spectrum in the low energy range. A tentative scaling of the previously measured CH3C3N ion yield by Lamarre et al. [17] is proposed, based on the comparison of the absorption data above the first ionization potential with the observed autoionization structures.
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Thon, R., Chin, W., Chamma, D., Galaup, J. - P., Ouvrard, A., Bourguignon, B., & Crépin, C. (2016). Vibrational spectroscopy and dynamics of W(CO)6in solid methane as a probe of lattice properties. J. Chem. Phys., 145(21), 214306.
Résumé: Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase. The vibrational dynamics of this mode is probed in stimulated photon echo experiments performed with a femtosecond IR laser. A short component around 10 ps is detected in the population relaxation lifetime in the high temperature phase of solid CH4 (phase I) and disappears at lower temperatures (phase II) where the vibrational lifetime is in the hundreds of ps. The analysis of the nonlinear time-resolved results suggests that the short component comes from a fast energy transfer between the vibrational excitation of the guest and the lattice in specific families of sites. Such fast transfers are observed in the case of W(CO)6 trapped in CD4 because of an energy overlap of the excitation of W(CO)6 and a lattice vibron. In solid CH4, even when these V-V transfers are not efficient, pure dephasing processes due to the molecular nature of the host occur: they are temperature dependent without a clear modification at the phase transition.
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2015 |
Arabei, S., McCaffrey, J. G., Galaup, J. - P., Shafizadeh, N., & Crepin, C. (2015). Stimulated emission in cryogenic samples doped with free-base tetraazaporphine. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17(22), 14931–42.
Résumé: Thin cryogenic samples of inert gas solids doped with free-base tetraazaporphine (H2TAP) were irradiated with a tunable pulsed laser. Under resonant electronic excitation of the guest, specific vibronic transitions of the fluorescence spectra were found to be strongly enhanced with only a moderate increase of the laser power. This enhancement is due to stimulated emission (SE). The characteristics of SE bands are described in the three hosts (Ar, N2, and Ne) explored, as well as their excitation spectra. SE is observed in transitions involving different vibrational modes of the guest, depending on the host and the electronic excitation. The results are discussed in comparison with previous works on other tetrapyrrolic molecules trapped in inert gas matrices. From this comparison the key features required to observe SE are deduced to be: (1) SE can be obtained with various tetrapyrrolic molecules; (2) free-base molecules are preferable to their metallo-counterparts; (3) the results highlight a specific molecular vibrational mode involved in the process; and (4) cryogenic crystal structures are also of importance in the detection of SE.
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Douin, S., Gronowski, M., Lamarre, N., Phung, V. - T., Boyé-Péronne, S., Crépin, C., & and Kołos, R. (2015). Cavity Ring Down Spectroscopy Measurements for High-Overtone Vibrational Bands of HC3N. Journal of Physical Chemistry A, 119(36), 9494–9505.
Résumé: Overtone (5ν1 and 6ν1) and combination (4ν1+ν3 and 4ν1+ν2) vibrational bands of gaseous HC3N, located in the visible range (14 600-15 800 cm-1 and 17 400-18 600 cm-1), were investigated by cavity ring-down absorption spectroscopy. The 5ν1+ν3 and 5ν1+ν2 combinations as well as the 6ν1+ν5-ν5 hot overtone band have also been identified, based on previous overtone assignments. Absolute integrated intensity values and the ensuing oscillator strengths have been measured here for the first time; f –values are typically confined between 4×10-12 and 7×10-11. For the even weaker 5ν1+ν2 combination band, the oscillator strength was estimated as 9×10-13.
The values concerning CH-stretch overtones (nν1) are similar to those found in the literature for HCN and C2H2, the molecules with sp-hybridized carbon atoms. Data presented here may prove useful for studying the photochemistry triggered with visible or near-IR radiation within the atmospheres of certain Solar System bodies, including Titan.
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Lozada-Garcia, R., Rojas-Lorenzo, G., Crepin, C., Ryan, M., & McCaffrey, J. G. (2015). Hg-Xe Exciplex Formation in Mixed Xe/Ar Matrices: Molecular Dynamics and Luminescence Study. Journal Of Physical Chemistry A, 119(11), 2307–2317.
Résumé: Luminescence of Hg(P-3(1)) atoms trapped in mixed Ar/Xe matrices containing a small amount of Xe is reported. Broad emission bands, strongly red-shifted from absorption are recorded which are assigned to strong complexes formed between the excited mercury Hg* and xenon atoms. Molecular dynamics calculations are performed on simulated Xe/Ar samples doped with Hg to follow the behavior of Hg* in the mixed rare gas matrices leading to exciplex formation. The role of Xe atoms in the first solvation shell (SS1) around Hg was investigated in detail, revealing the formation of two kinds of triatomic exciplexes; namely, Xe-Hg*-Xe and Ar-Hg*-Xe. The first species exists only when two xenon atoms are present in SS1 with specific geometries allowing the formation of a linear or quasi-linear exciplex. In the other geometries, or in the presence of only one Xe in SS1, a linear Ar-Hg*-Xe exciplex is formed. The two kinds of exciplexes have different emission bands, the most red-shifted being that involving two Xe atoms, whose emission is very close to that observed in pure Xe matrices. Simulations give a direct access to the analysis of the experimental absorption, emission, and excitation spectra, together with the dynamics of exciplexes formation.
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Turowski, M., Crepin, C., Douin, S., & Kolos, R. (2015). Formation and Spectroscopy of Dicyanotriacetylene (NC8N) in Solid Kr. Journal Of Physical Chemistry A, 119(11), 2701–2708.
Résumé: Thermally induced creation of dicyanotriacetylene (NC8N) was observed in solid krypton. Samples were obtained by cryogenic trapping of gaseous cyanoacetylene/Kr mixtures subjected to electric discharges. Strong a (3)Sigma(+)(u) -> X (1)Sigma(+)(g) phosphorescence of NC8N is reported here for the first time; its vibronic structure permitted the measurement of several ground-state vibrational frequencies. Other chemical species, mostly smaller than the precursor molecule, have also been formed, among them the dicarbon molecule (C-2), and these may serve as indispensable building blocks in the NC8N synthesis. Processes leading to the elongation of cyanoacetylenic chains are of potential importance for the chemistry of icy grains present in the interstellar gas clouds.
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2014 |
Chin, W., Chevalier, M., Thon, R., Pollet, R., Ceponkus, J., & Crepin, C. (2014). Photochemistry of glycolaldehyde in cryogenic matrices. JOURNAL OF CHEMICAL PHYSICS, 140(22), 224319.
Résumé: The photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization and fragmentation processes are found to compete. The hydrogen-bonded Cis-Cis form of GA is transformed mainly to the open Trans-Trans conformer and to CO and CH3OH fragments and their mixed complexes. Different photo-induced behaviours appear depending on the matrix. In nitrogen, small amounts of Trans-Gauche and Trans-Trans conformers are detected after deposition and grow together upon irradiation. The Trans-Gauche conformer is characterized for the first time. In para-hydrogen due to a weaker cage effect additional H2CO and HCO fragments are seen. Calculations of the potential energy surfaces of S-0, S-1, and T-1 states – to analyse the torsional deformations which are involved in the isomerization process – and a kinetic analysis are presented to investigate the different relaxation pathways of GA. Fragmentation of GA under UV irradiation through the CO+CH3OH molecular channel is a minor process, as in the gas phase. (C) 2014 AIP Publishing LLC.
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Couturier-Tamburelli, I., Pietri, N., Crepin, C., Turowski, M., Guillemin, J. - C., & Kolos, R. (2014). Synthesis and spectroscopy of cyanotriacetylene (HC7N) in solid argon. Journal Of Chemical Physics, 140(4), 044329.
Résumé: UV laser irradiations of cryogenic solid argon matrices doped with a mixture of acetylene and cyanodiacetylene (HC5N) resulted in the formation of a longer carbon-nitrogen chain, cyanotriacetylene (HC7N). The identification of this species was accomplished based on IR vibrational spectroscopy (including the study of isotopically labeled compounds), on electronic luminescence spectroscopy, and on theoretical predictions. Additionally, IR absorption bands recognized as due to HC7N were detected in photolysed Ar matrices doped with a cyanoacetylene/diacetylene mixture; this assignment was confirmed with the mass spectrometry of gases released upon the warm-up of the sample. (C) 2014 AIP Publishing LLC.
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Henchy, C., McCaffrey, J. G., Arabei, S., Pavich, T., Galaup, J. - P., Shafizadeh, N., & Crepin, C. (2014). Free base tetraazaporphine isolated in inert gas hosts: Matrix influence on its spectroscopic and photochemical properties. JOURNAL OF CHEMICAL PHYSICS, 141(12), 124303.
Résumé: The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H(2)TAP) trapped in Ne, N-2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H(2)TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H(2)TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Q(x) (0-0) absorption band made it possible to identify inter-conversion of distinct host sites.
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2013 |
Thon, R., Chin, W., Galaup, J. - P., Ouvrard, A., Bourguignon, B., & Crepin, C. (2013). Vibrational Perturbations of W(CO)(6) Trapped in a Molecular Lattice Probed by Linear and Nonlinear Spectroscopy. J. Phys. Chem. A, 117(34), 8145–8156.
Résumé: Vibrational dynamics of the T-1u CO stretching mode of tungsten hexacarbonyl is explored when the molecule is embedded in a nitrogen matrix at low temperature. Experiments combined infrared (IR) absorption spectroscopy and IR stimulated photon echoes at the femtosecond time scale. W(CO)(6) is found to be trapped in two main families of sites differing by their symmetry (called hereafter O-h and D-2h sites). In O-h sites, the vibrational coherence is strongly temperature dependent, exhibiting a coupling with librational phonons of the nitrogen lattice. Perturbation in D-2h sites results in the splitting of the T-1u band in three components. Each component is inhomogeneously broadened, with dephasing times in the tens of picoseconds, and is weakly coupled to the lattice phonons. Experiments in solid krypton are performed to compare the effect of atomic and diatomic host lattices. Dephasing time in Kr does not depend on temperature and remains in the hundreds of picoseconds, highlighting the molecular origin of the dephasing process in N-2. Additionally, nonlinear signals show oscillations due to quantum beats and polarization interferences between different frequency components of the induced third order polarization, giving information, in particular, on the overtone vibrational transition.
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2012 |
Arabei, S. M., Galaup, J. - P., McCaffrey, J. G., Shafizadeh, N., & Crepin, C. (2012). Electronic spectroscopy, stimulated emission, and persistent spectral hole burning of cryogenic nitrogen matrices doped with tetrabenzoporphin. LOW TEMPERATURE PHYSICS, 38(8), 727–731.
Résumé: This paper deals with our on-going work on the electronic spectroscopy of tetrapyrrole molecules embedded in cryogenic hosts. Under nanosecond laser excitation of free-base tetrabenzoporphin molecules in a nitrogen matrix at 8 K, increasing laser pulse energy results in essential enhancement of the intensity of one or several vibronic emission lines in the fine-structure fluorescence spectrum. Some characteristics of stimulated radiation are realized in the observed intense monochromatic: radiation as a result of a transition from the purely electronic S-1 level to a vibrational sublevel of the S-0 state, corresponding to the excitation of C-C stretching vibrations of tetrapyrrole methane bridges. We also report on persistent spectral hole-burning effects. Hole and antihole formation analysis gives some insight on the photochemical properties of tetrabenzoporphin in a nitrogen matrix. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746794]
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Henchy, C., Murray, C., Crepin, C., & McCaffrey, J. G. (2012). A DFT study of reversed isotope shifts in H/D substitution of free-base porphyrin and related free-base tetrapyrroles. Can. J. Chem.-Rev. Can. Chim., 90(12), 1078–1091.
Résumé: DFT/B3LYP calculations are used to analyse the occurrence of reverse isotope shift ratios (ISR) in H/D substitution of the free-base tetrapyrroles, in situations where the frequency ratio v(H)/v(D) is less than 1. The reverse ISR effect is found to be most evident in the out-of-plane bending modes (b(2g) and b(3u), symmetry) involving some N-H motion for the four molecules studied, viz., porphine (H2P), tetraaza-porphine (H(2)TAP), tetrabenzo-porphine (H2TBP), and phthalocyanine (H2Pc). It was analysed by following the evolution of the normal mode frequencies with incremental variation of the H atom masses from 1 to 2 amu. This method allows direct, unambiguous mode correlations to be established between the light and the heavy isotopologues. When the NH(D) motion is predominant, the H to D frequency evolution decreases in a continuous manner for a particular normal mode. In the case of two modes of the same symmetry and whose frequencies are similar, their frequency evolutions could cross, depending on the extent of NH(D) motion involved in them. The evolution diagrams may show avoided crossings of various extents, which thereby reflects the degree of the NH(D) motion in the modes. The reverse ISR effect is directly correlated to these avoided crossings. Because the isotope shifts are quite small (<10 cm(-1)) and occur in the congested 1500-500 cm(-1) spectral region, high-resolution methods yielding narrow line transitions are required for experimental analysis. The matrix isolation technique is particularly well suited for this work and is proposed for use in a search for this effect.
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Lozada-Garcia, R. R., Ceponkus, J., Chevalier, M., Chin, W., Mestdagh, J. - M., & Crepin, C. (2012). Nuclear Spin Conversion to Probe the Methyl Rotation Effect on Hydrogen-Bond and Vibrational Dynamics. Angewandte Chemie-International Edition, 51(28), 6947–6950.
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Lozada-Garcia, R. R., Ceponkus, J., Chevalier, M., Chin, W., Mestdagh, J. - M., & Crepin, C. (2012). Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation. Physical Chemistry Chemical Physics, 14(10), 3450–3459.
Résumé: The photochemistry of the chelated enol form of acetylacetone (AcAc) was investigated by UV excitation of the S2 state at 266 nm in parahydrogen matrices, complemented by experiments in neon and normal hydrogen matrices. Infrared (IR) spectroscopy, combined with theoretical calculations, was used to identify the photoproducts. Isomerization towards various non-chelated forms (no intramolecular H-bond) of AcAc is the dominant channel whereas fragmentation is very minor. The isomerization kinetics is monitored by IR spectroscopy. Among the seven non-chelated conformers of AcAc, only three are formed in parahydrogen matrices, whereas four are observed in normal hydrogen matrices. This difference suggests that an active tunnelling process between conformers occurs in parahydrogen but is quenched in normal hydrogen where guest-host interactions are stronger. Fragmentation and isomerization of excited AcAc are discussed in the light of these new data. The role of the intermediate triplet state in the S-2 -> S-0 relaxation is confirmed, as the importance of phonons in the condensed phase.
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Turowski, M., Crepin, C., Couturier-Tamburelli, I., Pietri, N., & Kolos, R. (2012). Low-temperature phosphorescence of dicyanoacetylene in rare gas solids. LOW TEMPERATURE PHYSICS, 38(8), 723–726.
Résumé: A strong visible a(similar to 3)Sigma(+)(u) – X-similar to 1 Sigma(+)(g) luminescence was observed upon UV excitation of cryogenic rare gas (argon, krypton, and xenon) matrices doped with dicyanoacetylene (NC4N). Spectra and life-times of this phosphorescence have been measured. A detailed analysis of resolved vibronic bands is presented. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745884]
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Turowski, M., Crepin, C., Douin, S., Gronowski, M., Couturier-Tamburelli, I., Pietri, N., Wasiak, A., & Kolos, R. (2012). Low temperature Raman spectra of cyanobutadiyne (HC5N). VIBRATIONAL SPECTROSCOPY, 62, 268–272.
Résumé: Low temperature Raman scattering spectra of cyanobutadiyne, either condensed from the vapour as a solid film, or isolated in a cryogenic argon matrix, have been measured – leading to the identification of all vibrational fundamentals, together with several overtones and combination modes. The analysis is based on previous experimental data, including the vibrationally resolved phosphorescence spectra, and on the comparison to available theoretical predictions. (C) 2012 Elsevier B.V. All rights reserved.
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2011 |
Crepin, C., Turowski, M., Ceponkus, J., Douin, S., Boye-Peronne, S., Gronowski, M., & Kolos, R. (2011). UV-induced growth of cyanopolyyne chains in cryogenic solids. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(37), 16780–16785.
Résumé: UV laser excitation of cryogenic solids doped with cyanoethyne, HC(3)N, led to an in situ creation of longer carbon-nitrogen chains, namely HC(5)N, C(4)N(2), and C(6)N(2), heralded by their strong visible luminescence. HC(5)N and C(4)N(2) molecules can form, most probably, within HC(3)N aggregates linked by hydrogen bonds, while the reaction occurring between two isolated, photochemically created C(3)N radicals yields C(6)N(2). This latter species, dicyanobutadiyne, is easily detected in Ar, Kr, N(2), as well as in parahydrogen solids. The C(6)N(2) phosphorescence is identified here for the first time. The reported carbon chain coupling reactions in rigid environments are of interest for astrochemistry of interstellar ices.
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Murray, C., Dozova, N., McCaffrey, J. G., Shafizadeh, N., Chin, W., Broquier, M., & Crepin, C. (2011). Visible luminescence spectroscopy of free-base and zinc phthalocyanines isolated in cryogenic matrices. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(39), 17543–17554.
Résumé: The absorption, emission and excitation spectra of ZnPc and H(2)Pc trapped in Ne, N(2), Ar, Kr and Xe matrices have been recorded in the region of the Q states. A comparison of the matrix fluorescence spectra with Raman spectra recorded in KBr pellets reveals very strong similarities. This is entirely consistent with the selection rules and points to the occurrence of only fundamental vibrational transitions in the emission spectra. Based on this behaviour, the vibronic modes in emission have been assigned using results obtained recently on the ground state with large basis-set DFT calculations [Murray et al. PCCP, 12, 10406 (2010)]. Furthermore, the very strong mirror symmetry between excitation and emission has allowed these assignments to be extended to the excitation (absorption) bands. While this approach works well for ZnPc, coupling between the band origin of the S(2)(Q(Y)) state and vibrationally excited levels of S(1)(Q(X)), limits the range of its application in H(2)Pc. The Q(X)/Q(Y) state coupling is analysed from data obtained from site-selective excitation spectra, revealing pronounced matrix and site effects. From this analysis, the splitting of the Q(X) and Q(Y) states has been determined more accurately than in any previous attempts.
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Vibrational Perturbations of W(CO)6 Trapped in a Molecular Lattice Probed by Linear and Nonlinear Spectroscopy. R. Thon, W. Chin, J.-P. Galaup, A. Ouvrard, B. Bourguignon, et C. Crepin - J. Phys. Chem. A 117 (2013) 8145-56
Nuclear Spin Conversion to Probe the Methyl Rotation Effect on Hydrogen-Bond and Vibrational Dynamics. R. R. Lozada-Garcia, J. Ceponkus, M. Chevalier, W. Chin, JM. Mestdagh, C. Crépin - Angew. Chem. Int. Ed. 51 (2012) 6947–6950
Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation. R. R. Lozada-Garcia, J. Ceponkus, M. Chevalier, W. Chin, JM. Mestdagh, C. Crépin - Phys. Chem. Chem. Phys. 14 (2012) 3450–3459
Visible luminescence spectroscopy of free-base and zinc phthalocyanines isolated in cryogenic matrices. C. Murray, N. Dozova, J. McCaffrey Phys. Chem. Chem. Phys. 13 (2011) 17543-17554
UV-induced growth of cyanopolyyne chains in cryogenic solids. C. Crépin, M. Turowski, J. Ceponkus, S. Douin, S. Boyé-Péronne, M. Gronowski, R. Kolos - Phys. Chem. Chem. Phys. 13 (2011) 16780-16785
Acetylacetone in hydrogen solids : IR signatures of the enol and keto tautomers and UV induced tautomerization. R. R. Lozada-Garcia, J. Ceponkus, W. Chin, M. Chevalier, C. Crépin - Chem. Phys. Lett. 504 (2011) 142
Infra-red and Raman spectroscopy of free-base and zinc phthalocyanines isolated in matrices. C. Murray, N. Dozova, J. McCaffrey, S. FitzGerald, N. Shafizadeh, C. Crépin - Phys. Chem. Chem. Phys. 12 (2010) 10406-10422
Infrared study of glycolaldehyde isolated in parahydrogen matrix.
J. Ceponkus, W. Chin, M. Chevalier, M. Broquier, A. Limongi, C. Crépin - J. Chem. Phys. 133 (2010) 094502