Isotopic substitution effects on acetic acid photofragmentation dynamics

Peterman, Dean R.; Daniel, Robert G.; Horwitz, Ronald J.; Guest, J. A.

doi:10.1016/0009-2614(95)00273-7

Cited by 21 publications

(21 citation statements)

References 26 publications

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“…As found before for other carboxylic acids that undergo decarboxylation or decarbonylation reactions upon UV irradiation, [54][55][56][57][58][59] the observed photochemical reactions in matrix-isolated PG shall involve radical intermediates resulting from α-cleavages either of the C-C α bond or C-O bond. This indicates that, with all probability, the decomposition reactions take place mainly on the excited state surfaces rather than in the vibrationally excited ground state.…”

Section: E Conformationally Dependent Uv-induced Photolysis Of Pg Monomer Isolated In a Xenon Matrixsupporting

confidence: 56%

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Borba

Gómez‐Zavaglia

Fausto

2014

The Journal of Chemical Physics

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The conformational space of α-phenylglycine (PG) have been investigated theoretically at both the DFT/B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of approximation. Seventeen different minima were found on the investigated potential energy surfaces, which are characterized by different dominant intramolecular interactions: type I conformers are stabilized by hydrogen bonds of the type N-H···O=C, type II by a strong O-H···N hydrogen bond, type III by weak N-H···O-H hydrogen bonds, and type IV by a C=O···H-C contact. The calculations indicate also that entropic effects are relevant in determining the equilibrium populations of the conformers of PG in the gas phase, in particular in the case of conformers of type II, where the strong intramolecular O-H···N hydrogen bond considerably diminishes entropy by reducing the conformational mobility of the molecule. In consonance with the relative energies of the conformers and barriers for conformational interconversion, only 3 conformers of PG were observed for the compound isolated in cryogenic Ar, Xe, and N2 matrices: the conformational ground state (ICa), and forms ICc and IITa. All other significantly populated conformers existing in the gas phase prior to deposition convert either to conformer ICa or to conformer ICc during matrix deposition. The experimental observation of ICc had never been achieved hitherto. Narrowband near-IR irradiation of the first overtone of νOH vibrational mode of ICa and ICc in nitrogen matrices (at 6910 and 6930 cm(-1), respectively) led to selective generation of two additional conformers of high-energy, ITc and ITa, respectively, which were also observed experimentally for the first time. In addition, these experiments also provided the key information for the detailed vibrational characterization of the 3 conformers initially present in the matrices. On the other hand, UV irradiation (λ = 255 nm) of PG isolated in a xenon matrix revealed that PG undergoes facile photofragmentation through two photochemical pathways that are favored for different initial conformations of the reactant: (a) decarboxylation, leading to CO2 plus benzylamine (the dominant photofragmentation channel in PG cis-COOH conformers ICa and ICc) and (b) decarbonylation, with generation of CO plus benzonitrile, H2O and H2 (prevalent in the case of the trans-COOH conformer, IITa).

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Section: E Conformationally Dependent Uv-induced Photolysis Of Pg Monomer Isolated In a Xenon Matrixsupporting

confidence: 56%

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Borba

Gómez‐Zavaglia

Fausto

2014

The Journal of Chemical Physics

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“…The mechanisms of the photolysis processes cannot be unequivocally established on the basis of the experiments here described. However the photochemical reactions shall involve radical intermediates resulting from a-cleavages either of the C-C a bond or C-O bond, as found previously for most of the carboxylic acids that undergo decarboxylation or decarbonylation reactions upon UV irradiation [31][32][33][34][35][36]. This indicates that the decomposition reactions shall take place mainly on the excited state surfaces rather than in the vibrationally excited ground state.…”

Section: Resultsmentioning

confidence: 57%

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Jarmelo

Fausto

2006

Journal of Molecular Structure

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Monomeric serine can be trapped in low temperature argon matrices in different conformers, which can be classified in three groups (A, B, C) accordingly to the main intramolecular interaction they exhibit: A (OH A /N hydrogen bond), B (OH C /N) and C (OH A /Oa) (subscripts A and C stand for alcohol and carboxylic group, respectively). The OH C /N intramolecular interaction found in B-type conformers is considerably stronger than both the OH A /N and OH A /Oa hydrogen bonds, and leads to reduce the abundance of B-type form relatively to A and C forms at high temperatures due to entropy effects. When submitted to UV irradiation (lO200 nm), the main observed photoprocess is decarboxylation, leading to production of CO 2 and ethanolamine. A less important photochemical process is also observed, where the compound undergoes decarbonylation, with formation of CO, H 2 O and acetamide. The two observed photoprocesses were found to be dependent on the conformation assumed by the reactant molecule, with Aand C-type conformers of serine undergoing decarboxylation and B-type conformers decarbonylation.

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“…Photodissociation of small, saturated carboxylic acids such as formic (HCOOH) and acetic acid (CH 3 COOH) has been of great interest because of the acids’ atmospheric, combustion, and interstellar chemistry. Photodissociation dynamics of acetic acid has been thoroughly investigated because the molecule is large enough to show multiple dissociation pathways but small enough to probe underlying dissociation dynamics in detail. − The UV absorption spectrum shows continuous absorption starting from 250 nm and a maximum near 210 nm, where this absorption band has been assigned as the n → π* transition. , Upon electronic excitation to its 1 (n,π*)(A″) state near 210 nm, the following primary decomposition processes can take place. …”

Section: Introductionmentioning

confidence: 99%

“…Although the OH production channels from acetic acid have been studied in detail, the H atom production channels, reactions 4 production channels from photodissociation of formic acid in the (n,π*) 1,3 state at 205 nm were studied by measuring Doppler broadened H atom spectra. 13 From the spectra, the translational energy releases in the H atom production channels were measured.…”

Section: ■ Introductionmentioning

confidence: 99%

Dynamics of H Atom Production from Photodissociation of Acetic Acid-d₁

2015

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Detailed dissociation dynamics of H(D) from acetic acid-d1 (CH3COOD) has been investigated upon electronic excitation to the (1)(n,π*), S1 state at 205 nm by measuring laser-induced fluorescence spectra of the fragment H(D) atoms. In addition, quantum yields for the H(D) atom dissociation channels, CH3COO + D and CH2COOD + H, were measured, which are 0.07 ± 0.03 and 0.17 ± 0.03, respectively. From the Doppler broadened spectra, the center-of-mass translational energy releases into products were obtained. To determine the detailed dissociation dynamics, two-dimensional potential energy surfaces along the reaction coordinate including the coordinate directly coupled to the dissociation coordinate were examined by employing quantum chemical calculations. For the CH3COO + D channel, the coupled coordinate is the dihedral angle of D against the COO plane. The dissociation of D(H) from acetic acid should take place along the triplet surface via surface crossing from the initially excited S1 state. Along the triplet surface, an exit channel barrier exists, which originates from the structural difference between the T1 and the product asymptotes, especially the dihedral angle of D against the COO plane. The observed translational energy releases were successfully estimated by the barrier impulsive model based upon the calculated two-dimensional potential energy surfaces at the B3LYP/cc-pVDZ level of theory.

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Isotopic substitution effects on acetic acid photofragmentation dynamics

Cited by 21 publications

References 26 publications

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Dynamics of H Atom Production from Photodissociation of Acetic Acid-d₁

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Isotopic substitution effects on acetic acid photofragmentation dynamics

Cited by 21 publications

References 26 publications

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Conformers, infrared spectrum, UV-induced photochemistry, and near-IR-induced generation of two rare conformers of matrix-isolated phenylglycine

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Dynamics of H Atom Production from Photodissociation of Acetic Acid-d1

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Dynamics of H Atom Production from Photodissociation of Acetic Acid-d₁