Peer-reviewed Publications |
Alata, I., Broquier, M., Dedonder-Lardeux, C., Jouvet, C., Kim, M., Sohn, W. Y., Kim, S. -su, Kang, H., Schutz, M., Patzer, A., & Dopfer, O. (2011). Microhydration effects on the electronic spectra of protonated polycyclic aromatic hydrocarbons: [naphthalene-(H2O)(n = 1,2)]H+. J Chem Phys, 134(7), 074307.
Résumé: Vibrational and electronic spectra of protonated naphthalene (NaphH(+)) microsolvated by one and two water molecules were obtained by photofragmentation spectroscopy. The IR spectrum of the monohydrated species is consistent with a structure with the proton located on the aromatic molecule, NaphH(+)-H(2)O. Similar to isolated NaphH(+), the first electronic transition of NaphH(+)-H(2)O (S(1)) occurs in the visible range near 500 nm. The doubly hydrated species lacks any absorption in the visible range (420-600 nm) but absorbs in the UV range, similar to neutral Naph. This observation is consistent with a structure, in which the proton is located on the water moiety, Naph-(H(2)O)(2)H(+). Ab initio calculations for [Naph-(H(2)O)(n)]H(+) confirm that the excess proton transfers from Naph to the solvent cluster upon attachment of the second water molecule.
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Chakraborty, A., Guchhait, N., Le Barbu-Debus, K., Mahjoub, A., Lepere, V., & Zehnacker-Rentien, A. (2011). Role of Conformational Isomerism in Solvent-Mediated Charge Transfer in Chiral (S) 1,2,3,4-Tetrahydro-3-isoquinoline Methanol (THIQM): Condensed-Phase to Jet-Cooled Spectroscopic Studies. JOURNAL OF PHYSICAL CHEMISTRY A, 115(34), 9354–9364.
Résumé: Intramolecular charge-transfer reaction in chiral (S) 1,2,3,4-tetrahydro3-isoquinoline methanol (THIQM) has been investigated in the condensed phase and in jet-cooled conditions by means of laser-induced fluorescence, dispersed emission, resonance-enhanced two-photon ionization, and IR-UV double resonance experiments, as well as quantum chemical calculations. In the condensed phase, THIQM only shows local emission in nonpolar and protic solvents and dual emission in aprotic polar solvents, where the solvent-polarity dependent Stokes shifted emission is ascribed to a state involving charge transfer from the nitrogen lone pair to the benzene pi-cloud. Ab initio calculations reveal two low-energy conformers, which are observed in jet-cooled conditions. In the most stable conformer, THIQM(1), the CH(2)OH substituent acts as a hydrogen bond donor to the nitrogen lone pair in the equatorial position, while the second most stable conformer, THIQM(II), corresponds to the opposite NH center dot center dot center dot O hydrogen bond, with the nitrogen lone pair in the axial position. The two low-energy jet-cooled conformers of THIQM evidenced from the laser-induced fluorescence and dispersed emission spectra only show structured local emission. Complexes with usual solvents reproduce the condensed phase properties. The jet-cooled complex with aprotic polar, solvent acetonitrile shows both local emission and charge transfer emission as observed in solution. The jet-cooled hydrate mainly shows local emission due to the unavailability of the nitrogen lone pair through intermolecular hydrogen bonding.
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Champeaux, J. P., Carcabal, P., Sence, M., Moretto-Capelle, P., & Cafarelli, P. (2011). A simple 'statistical' approach for fragmentation studies of doubly ionized cytosine, thymine and uracil bases. J. Phys. B-At. Mol. Opt. Phys., 44(4), 045205.
Résumé: A simple statistical model describing the dissociation of molecular dications into correlated fragment pairs has been developed. This model is based on a combinatory approach in which all possible fragments are enumerated and is refined by taking into account the initial structure of the parent molecule, considering the number of chemical bonds to be broken to give rise to the fragments. We show how this model can be used as a tool to help interpret experimental results of coincidence experiments. It shows that dissociation of doubly ionized molecules upon 100 keV proton irradiation is dominated by statistical processes but it also enables easy identification of the dissociation products originating from non-statistical processes requiring further investigation, possibly conveying information on the radiation-molecule interaction itself.
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Cheong, N. R., Nam, S. H., Park, H. S., Ryu, S., Song, J. K., Park, S. M., Perot, M., Lucas, B., Barat, M., Fayeton, J. A., & Jouvet, C. (2011). Photofragmentation in selected tautomers of protonated adenine. Phys Chem Chem Phys, 13(1), 291–295.
Résumé: The photofragmentation by UV excitation of selectively prepared 1(+) and 3(+) tautomers of protonated adenine is studied after excitation at a 266 and 263 nm wavelengths with two different experimental set-ups located in Seoul and Orsay. While the production of 1(+) tautomers with an electrospray ion source is now well accepted, calculations were used to ascribe the preparation of 3(+) tautomers from cold adenine dimers. The fragmentation patterns are rather similar for both tautomers, suggesting similar mechanisms as a statistical fragmentation in the ground electronic state after internal conversion.
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Cocinero, E. J., Carcabal, P., Vaden, T. D., Davis, B. G., & Simons, J. P. (2011). Exploring Carbohydrate-Peptide Interactions in the Gas Phase: Structure and Selectivity in Complexes of Pyranosides with N-Acetylphenylalanine Methylamide. J. Am. Chem. Soc., 133(12), 4548–4557.
Résumé: The physical basis of carbohydrate-peptide interactions has been explored by probing the structures of a series of complexes generated in a solvent-free environment under molecular beam conditions. A combination of double-resonance IR-UV spectroscopy and quantum-chemical calculations has established the structures of complexes of the model, N-acetyl-L-phenylalanine methylamide, bound to the alpha and beta anomers of methyl D-gluco- and D-galactopyranoside as guests. In all cases, the carbohydrates are bound through hydrogen bonding to the dipeptide chain, although with some differing patterns. The amino acid host “engages” with the most suitable pair of neighboring conjugate sites on each carbohydrate; the specific choice depends on the conformation of the peptide backbone and the configuration and conformation of the carbohydrate ligand. None of the structures is supported by “stacking” interactions with the aromatic ring, despite their common occurrence in bound carbohydrate-protein structures.
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Cocinero, E. J., Carcabal, P., Vaden, T. D., Simons, J. P., & Davis, B. G. (2011). Sensing the anomeric effect in a solvent-free environment. Nature, 469(7328), 76–U1400.
Résumé: The anomeric effect is a chemical phenomenon(1-9) that refers to an observed stabilization(10) of six-membered carbohydrate rings when they contain an electronegative substituent at the C1 position of the ring. This stereoelectronic effect influences the three-dimensional shapes of many biological molecules. It can be manifested not only in this classical manner involving interaction of the endocyclic oxygen atom (O5) found in such sugars with the C1 substituent (endo-anomeric effect) but also through a corresponding interaction of the electronegative exocyclic substituent with O5 (exoanomeric effect). However, the underlying physical origin(s) of this phenomenon is still not clear(1,3,4,11-14). Here we show, using a combination of laser spectroscopy and computational analysis, that a truncated peptide motif can engage the two anomers of an isolated sugar in the gas phase, an environment lacking extraneous factors which could confound the analysis. (Anomers are isomers that differ in the orientation of the substituent at C1.) Complexes formed between the peptide and the alpha- or beta-anomers of D-galactose are nearly identical structurally; however, the strength of the polarization of their interactions with the peptide differs greatly. Natural bond order calculations support this observation, and together they reveal the dominance of the exo- over the endo-anomeric effect. As interactions between oxygen atoms at positions C1 and C2 (O1 and O2, respectively) on the pyranose ring can alter the exo/endo ratio of a carbohydrate, our results suggest that it will be important to reevaluate the influence, and biological effects, of substituents at position C2 in sugars.
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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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Gans, B., Boye-Peronne, S., Broquier, M., Delsaut, M., Douin, S., Fellows, C. E., Halvick, P., Loison, J. - C., Lucchese, R. R., & Gauyacq, D. (2011). Photolysis of methane revisited at 121.6 nm and at 118.2 nm: quantum yields of the primary products, measured by mass spectrometry. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(18), 8140–8152.
Résumé: Methane photolysis has been performed at the two Vacuum UltraViolet (VUV) wavelengths, 121.6 nm and 118.2 nm, via a spectrally pure laser pump-probe technique. The first photon is used to dissociate methane (either at 121.6 nm or at 118.2 nm) and the second one is used to ionise the CH(2) and CH(3) fragments. The radical products, CH(3)(X), CH(2)(X), CH(2)(a) and C((1)D), have been selectively probed by mass spectrometry. In order to quantify the fragment quantum yields from the mass spectra, the photoionisation cross sections have been carefully evaluated for the CH(2) and CH(3) radicals, in two steps: first, theoretical ab initio approaches have been used in order to determine the pure electronic photoionisation cross sections of CH(2)(X) and CH(2)(a), and have been rescaled with respect to the measured absolute photoionisation cross section of the CH(3)(X) radical. In a second step, in order to take into account the substantial vibrational energy deposited in the CH(3)(X) and CH(2)(a) radicals, the variation of their cross sections near threshold has been simulated by introducing the pertinent Franck-Condon overlaps between neutral and cation species. By adding the interpolated values of CH quantum yields measured by Rebbert and Ausloos [J. Photochem., 1972, 1, 171-176], a complete set of fragment quantum yields has been derived for the methane photodissociation at 121.6 nm, with carefully evaluated 1 sigma uncertainties: Phi[CH(3)(X)] = 0.42 +/- 0.05, Phi[CH(2)(a)] = 0.48 +/- 0.05, Phi[CH(2)(X)] = 0.03 +/- 0.08, Phi[CH(X)] = 0.07 +/- 0.01. These new data have been measured independently of the H atom fragment quantum yield, subject to many controversies in the literature. From our results, we evaluate Phi(H) = 0.55 +/- 0.17 at 121.6 nm. The quantum yields for the photolysis at 118.2 nm differ notably from those measured at 121.6 nm, with a substantial production of the CH(2)(X) fragment: Phi[CH3(X)] = 0.26 +/- 0.04, Phi[CH(2)(a)] = 0.17 +/- 0.05, Phi[CH(2)(X)] = 0.48 +/- 0.06, Phi[CH(X)] = 0.09 +/- 0.01, Phi(H) = 1.31 +/- 0.13. These new data should bring reliable and essential inputs for the photochemical models of the Titan atmosphere.
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Goulay, F., Soorkia, S., Meloni, G., Osborn, D. L., Taatjes, C. A., & Leone, S. R. (2011). Detection of pentatetraene by reaction of the ethynyl radical (C2H) with allene (CH2=C=CH2) at room temperature. Phys. Chem. Chem. Phys., 13(46), 20820–20827.
Résumé: The reaction of ethynyl radical (C(2)H) with allene (C(3)H(4)) at room temperature is investigated using an improved synchrotron multiplexed photoionization mass spectrometer (MPIMS) coupled to tunable vacuum ultraviolet (VUV) synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory (LBNL). The orthogonal-accelerated time-of-flight mass spectrometer (OA-TOF) compared to the magnetic sector mass spectrometer used in a previous investigation of the title reaction (Phys. Chem. Chem. Phys., 2007, 9, 4291) enables more sensitive and selective detection of low-yield isomeric products. The C(5)H(4) isomer with the lowest ionization energy, pentatetraene, is now identified as a product of the reaction. Pentatetraene is predicted to be formed based on recent ab initio/RRKM calculations (Phys. Chem. Chem. Phys., 2010, 12, 2606) on the C(5)H(5) potential energy surface. However, the computed branching fraction for pentatetraene is predicted to be five times higher than that for methyldiacetylene, whereas experimentally the branching fraction of pentatetraene is observed to be small compared to that of methyldiacetylene. Although H-atom assisted isomerization of the products can affect isomer distribution measurements, isomerization has a negligible effect in this case. The kinetic behavior of the several C(5)H(4) isomers is identical, as obtained by time-dependent photoionization spectra. Even for high allene concentrations (and hence higher H-atom concentrations) no decay of the pentatetraene fraction is observed, indicating that H-assisted isomerization of pentatetraene to methyldiacetylene does not account for the difference between the experimental data and the theoretical branching ratios.
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Kumar, S. S., Perot-Taillandier, M., Lucas, B., Soorkia, S., Barat, M., & Fayeton, J. A. (2011). UV Photodissociation Dynamics of Deprotonated 2 '-Deoxyadenosine 5 '-Monophosphate [5 '-dAMP-H](-). JOURNAL OF PHYSICAL CHEMISTRY A, 115(38), 10383–10390.
Résumé: The UV photodissociation dynamics of deprotonated 2'-deoxyadenosine 5'-monophosphate ([5'-dAMP-H](-)) has been studied using a unique technique based on the coincident detection of the ion and the neutral fragments. The observed fragment ions are m/z 79 (PO3-), 97 (H2PO4-), 134 ([A-H](-)), 177 ([dAMP-H-A-H2O](-)), and 195 ([dAMP-H-A](-)), where “A” refers to a neutral adenine molecule. The relative abundances are comparable to that found in previous studies on [5'-dAMP-H](-) employing different excitation processes, i.e., collisions and UV photons. The fragmentation times of the major channels have been measured, and are all found to be on the microsecond time scale. The fragmentation mechanisms for all channels have been characterized using velocity correlation plots of the ion and neutral fragment(s). The findings show that none of the dissociation channels of [5'-dAMP-H](-) is UV specific and all proceed via statistical fragmentation on the ground state after internal conversion, a result similar to fragmentations induced by collisions.
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Le Barbu-Debus, K., Sen, A., Broquier, M., & Zehnacker, A. (2011). Jet-cooled hydrates of Chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM): structure and mechanism of formation. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(31), 13985–13991.
Résumé: The mechanism of formation of hydrates of chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline (THIQM) with two water molecules has been investigated in jet-cooled condition by means of resonance-enhanced two-photon ionization and IR-UV double resonance experiments. Quantum chemical calculations reveal that only one isomer of the THIQM is involved in the THIQM-(H(2)O)(2) complex formation, in contrast with what was observed for THIQM-(H(2)O). Anharmonic vibration calculations allowed unambiguous assignment of THIQM-(H(2)O)(2) to a complex resulting from the addition of a water molecule on the most stable THIQM-(H(2)O) complex. A sequential mechanism for complex formation has been deduced from these results.
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Lozada-Garcia, R. R., Ceponkus, J., Chin, W., Chevalier, M., & Crepin, C. (2011). Acetylacetone in hydrogen solids: IR signatures of the enol and keto tautomers and UV induced tautomerization. CHEMICAL PHYSICS LETTERS, 504(4-6), 142–147.
Résumé: Acetylacetone is isolated in hydrogen matrices and is investigated by means of infrared spectroscopy, combined with theoretical calculations. The two stable enol and keto tautomers are well characterized. The keto/enol ratio in solid parahydrogen is found to be higher than in classical matrices. While vibrational bands of the enol form are broad, with bandwidths depending on the vibrational mode, those of the keto form are narrow. A KrF laser excitation is used to induce the enol/keto tautomerization in solid parahydrogen. The kinetics of the interconversion is followed, highlighting a non-direct tautomerization process. (C) 2011 Elsevier B. V. All rights reserved.
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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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Scuderi, D., Le Barbu-Debus, K., & Zehnacker, A. (2011). The role of weak hydrogen bonds in chiral recognition. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(40), 17916–17929.
Résumé: Chiral recognition has been studied in neutral or ionic weakly bound complexes isolated in the gas phase by combining laser spectroscopy and quantum chemical calculations. Neutral complexes of the two enantiomers of lactic ester derivatives with chiral chromophores have been formed in a supersonic expansion. Their structure has been elucidated by means of IR-UV double resonance spectroscopy in the 3 mm region. In both systems described here, the main interaction ensuring the cohesion of the complex is a strong hydrogen bond between the chromophore and methyl-lactate. However, an additional hydrogen bond of much weaker strength plays a discriminative role between the two enantiomers. For example, the 1 : 1 heterochiral complex between R-(+)-2-naphthyl-ethanol and S-(+) methyl-lactate is observed, in contrast with the 1 : 1 homochiral complex which lacks this additional hydrogen bond. On the other hand, the same kind of insertion structures is formed for the complex between S-( +/-)-cis-1-amino-indan-2-ol and the two enantiomers of methyl-lactate, but an additional addition complex is formed for R-methyl-lactate only. This selectivity rests on the formation of a weak CH center dot center dot center dot pi interaction which is not possible for the other enantiomer. The protonated dimers of Cinchona alkaloids, namely quinine, quinidine, cinchonine and cinchonidine, have been isolated in an ion trap and studied by IRMPD spectroscopy in the region of the nu(OH) and nu( NH) stretch modes. The protonation site is located on the alkaloid nitrogen which acts as a strong hydrogen bond donor in all the dimers studied. While the nature of the intermolecular hydrogen bond is similar in the homochiral and heterochiral complexes, the heterochiral complex displays an additional weak CH center dot center dot center dot O hydrogen bond located on its neutral part, which results in slightly different spectroscopic fingerprints in the n( OH) stretch region. This first spectroscopic evidence of chiral recognition in protonated dimers opens the way to the study of the complexes of Cinchona alkaloids involved in enantioselective catalysis. These examples show how secondary hydrogen bonds controlled by stereochemical factors govern molecular recognition processes.
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Sepiol, J., Grabowska, A., Borowicz, P., Kijak, M., Broquier, M., Jouvet, C., Dedonder-Lardeux, C., & Zehnacker-Rentien, A. (2011). Excited-state intramolecular proton transfer reaction modulated by low-frequency vibrations: An effect of an electron-donating substituent on the dually fluorescent bis-benzoxazole. JOURNAL OF CHEMICAL PHYSICS, 135(3), 034307.
Résumé: Excited-state intramolecular proton transfer (ESIPT) reaction has been studied in a molecule showing dual fluorescence, the 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP), and its isotopomers, where the methoxy, and alternatively, the OH group has been deuterated. Attention is focused on the influence of electron donating OCH3 substituent on fast excited state reaction. Comparison between the resonance-enhanced multiphoton ionization spectrum and the laser-induced excitation of the primary and phototautomeric emissions has been done. The geometry, electron density distribution, vibrational structure as well as the potential energy profiles in the S-0 and S-1 states of four possible rotameric forms of BBMP were calculated with application of the density functional theory (DFT). It allowed identifying the most probable conformer and assessing the role of low-frequency motions for the ESIPT efficiency. (C) 2011 American Institute of Physics. [doi:10.1063/1.3609759]
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Soorkia, S., Liu, C. - L., Savee, J. D., Ferrell, S. J., Leone, S. R., & Wilson, K. R. (2011). Airfoil sampling of a pulsed Laval beam with tunable vacuum ultraviolet synchrotron ionization quadrupole mass spectrometry: application to low-temperature kinetics and product detection. Rev. Sci. Instrum., 82(12), 124102.
Résumé: A new pulsed Laval nozzle apparatus with vacuum ultraviolet (VUV) synchrotron photoionization quadrupole mass spectrometry is constructed to study low-temperature radical-neutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets. A design for the sampling geometry of a pulsed Laval nozzle expansion has been developed that operates successfully for the determination of rate coefficients by time-resolved mass spectrometry. The new concept employs airfoil sampling of the collimated expansion with excellent sampling throughput. Time-resolved profiles of the high Mach number gas flow obtained by photoionization signals show that perturbation of the collimated expansion by the airfoil is negligible. The reaction of C(2)H with C(2)H(2) is studied at 70 K as a proof-of-principle result for both low-temperature rate coefficient measurements and product identification based on the photoionization spectrum of the reaction product versus VUV photon energy. This approach can be used to provide new insights into reaction mechanisms occurring at kinetic rates close to the collision-determined limit.
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Soorkia, S., Shafizadeh, N., Lievin, J., Gaveau, M. - A., Pothier, C., Mestdagh, J. - M., Soep, B., & Field, R. W. (2011). Determination of the Ground Electronic State in Transition Metal Halides: ZrF. J. Phys. Chem. A, 115(34), 9620–9632.
Résumé: The spectroscopy of the ZrF radical, produced by a laser ablation molecular beam experimental setup, has been investigated for the first time using a two-color two-photon (1 + 1') REMPI scheme and time-of-flight (TOF) mass spectrometry detection. The region of intense bands 400-470 nm has been studied, based upon the first spectroscopic observations of the isovalent ZrCl radical by Carroll and Daly.(1) The overall spectrum observed is complex. However, simultaneous and individual ion detection of the five naturally occurring isotopologues of ZrF has provided a crucial means of identifying band origins and characterization via the isotopic shift, delta(iso), of the numerous vibronic transitions recorded. Hence, five (0-0) transitions, of which only two were free of overlap with other transitions, have been identified. The most intense (0-0) transition at 23113 cm(-1) presented an unambiguously characteristic RQP rotational structure. From rotational contour simulations of the observed spectra, the nature of the ground electronic state is found to be unambiguously of (2)Delta symmetry, leading to the assignment of this band as (0-0) (2)Delta <- X(2)Delta at 23113 cm(-1). A set of transitions (1-0) (2)Delta <- X(2)Delta at 22105 cm(-1) and (2-0) (2)Phi <- X(2)Delta at 22944 cm(-1) involving the X(2)Delta state has also been identified and analyzed. Furthermore, a second series of transitions with lesser intensity has also been related to the long-lived metastable (4)Sigma(-) state: (3-0) (4)Pi(-1/2) <- (4)Sigma(-) at 21801 cm(-1), (2-0) (4)Pi(-1/2) <- (4)Sigma(-) at 21285 cm(-1) and (2-0) (4)Sigma(-) <- (4)Sigma(-) at 23568 cm(-1). These spectroscopic assignments are supported by MRCI ab initio calculations, performed using the MOLPRO quantum chemistry package, and show that the low-lying excited states of the ZrF radical are the (4)Sigma(-) and (4)Phi states lying at 2383 and 4179 cm(-1) respectively above the ground X (2)Delta state. The difference in the nature of ground state and ordering of the first electronic states with TiF (X (4)Phi)(2-4) and ZrCl,(s) respectively, is examined in terms of the ligand field theory (LFT)(7) applied to diatomic molecules. These results give a precise description of the electronic structure of the low lying electronic states of the ZrF transition metal radical.
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Trevitt, A. J., Soorkia, S., Savee, J. D., Selby, T. S., Osborn, D. L., Taatjes, C. A., & Leone, S. R. (2011). Branching fractions of the CN + C3H6 reaction using synchrotron photoionization mass spectrometry: evidence for the 3-cyanopropene product. J. Phys. Chem. A, 115(46), 13467–13473.
Résumé: The gas-phase CN + propene reaction is investigated using synchrotron photoionization mass spectrometry (SPIMS) over the 9.8-11.5 eV photon energy range. Experiments are conducted at room temperature in 4 Torr of He buffer gas. The CN + propene addition reaction produces two distinct product mass channels, C(3)H(3)N and C(4)H(5)N, corresponding to CH(3) and H elimination, respectively. The CH(3) and H elimination channels are measured to have branching fractions of 0.59 +/- 0.15 and 0.41 +/- 0.10, respectively. The absolute photoionization cross sections between 9.8 and 11.5 eV are measured for the three considered H-elimination coproducts: 1-, 2-, and 3-cyanopropene. Based on fits using the experimentally measured photoionization spectra for the C(4)H(5)N mass channel and contrary to the previous study (Int. J. Mass. Spectrom.2009, 280, 113-118), where it was concluded that 3-cyanopropene was not a significant product, the new data suggests 3-cyanopropene is produced in significant quantity along with 1-cyanopropene, with isomer branching fractions from this mass channel of 0.50 +/- 0.12 and 0.50 +/- 0.24, respectively. However, similarities between the 1-, 2-, and 3-cyanopropene photoionization spectra make an unequivocal assignment difficult based solely on photoionization spectra. The CN + CH(2)CHCD(3) reaction is studied and shows, in addition to the H-elimination product signal, a D-elimination product channel (m/z 69, consistent with CH(2)CHCD(2)CN), providing further evidence for the formation of the 3-cyanopropene reaction product.
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