The conformational changes accompanying the  triplet–singlet electronic excitation of acetaldehyde, CH<sub>3</sub>CHO

Moule, D. C.; Ng, Kim Hok-kin.

doi:10.1139/v85-236

Cited by 30 publications

(14 citation statements)

References 8 publications

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“…Comparison may be made between the calculated energies and those previously obtained by theory or experiment. The triplet acetaldehyde is calculated to lie 74·0 kcal mol Ϫ 1 above the ground state in good agreement with the experimentally 18 obtained value of 77·8 kcal mol Ϫ 1 . The CO+CH 4 dissociation limit is estimated [calculated from the thermochemistry of the reaction CH 3 CHO (S 0 )→CH 4 + CO in the gaseous state; enthalpies of activa-tion obtained from Ref.…”

Section: Energiessupporting

confidence: 84%

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

BelBruno

1997

J. Phys. Org. Chem.

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Ab initio calculations, including electron correlation, were employed to compute the geometries and energies of all stable C 2 H 4 O species, as well as four transition states along the potential surfaces connecting oxirane to the unimolecular dissociation products. The calculations indicate that the primary step in the major reaction observed experimentally is the isomerization of oxirane along the ground-state potential surface to acetaldehyde. Calculations indicate that the experimental reaction products are derived from unimolecular decomposition on the acetaldehyde S 0 surface (CH 4 + CO) or, after intersystem crossing, along the lowest triplet state of acetaldehyde (CH 3 + HCO). Additional pathways connecting oxirane to a number of less energetically favorable ring-opened or fragmentation products are also presented.

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Section: Energiessupporting

confidence: 84%

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

BelBruno

1997

J. Phys. Org. Chem.

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“…1. Using the torsional transitions in X'A' states from microwave and far infrared (2, 3) spectra, we assigned selected bands to the torsional 15$ vibronic transitions.…”

Section: Resultsmentioning

confidence: 99%

“…The h3A" +-X'A' electronic absorption spectrum of acetaldehyde-h4 in the vapour phase at room temperature was investigated earlier by Moule and Ng (1). This spectrum was interpreted in terms of the torsional modes v;, and v ' , ' , attached to the v;, out-of-plane C-H bending mode.…”

Section: Calibration Was Made With the Iron Lines Of An Iron-neon Hol-mentioning

confidence: 90%

The electronic spectra of acetaldehyde-h₄ and -d₄

Yakovlev¹,

Godunov²

1992

Can. J. Chem.

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N. N. YAKOVLEV and I. A. GODUNOV. Can. J. Chem. 70, 931 (1992).The r 7 3~" t X'A' electronic absorption spectra of acetaldehyde-h4 and -d4 were recorded in the vapour phase at room temperature. The major experimental requirement was a high pressure X path length (650 Torr X 140 m). The vibrational structure of these electronic transitions was interpreted in terms of the torsional modes vj5 and vy5 attached to the vi4 out-of-plane bending mode. The main CH3CH0 results agreed with those obtained earlier (Moule and Ng); the values of the 0: transition and torsional barrier height were 27240.1 and 590 cm-' respectively. Three inversion (out-ofplane bending) energy levels in the excited ti3A" state were found and the inversion potential function was determined with a barrier height of 11 10 cm-I. The CD3CD0 spectrum confirmed the CH,CHO analysis. The values of the 0: transition and torsional barrier height were equal to 27270 and 610 cm-I.

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“…[5][6][7][8][9][10][11] Experimental studies of the structure of conforma tionally flexible molecules (especially if they are in ex cited electronic states) face severe difficulties, which are first of all associated with possible ambiguity of band as signment in the vibronic spectra and instability of inverse problems of the determination of potentials of internal rotation and inversion. Therefore, quantum mechanical calculations can serve as both an additional source of structural information and a method of analysis of the nature of conformational effects.…”

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confidence: 99%

Structure of acetyl chloride molecule isotopomers CH3COCl and CD3COCl in the ground and lowest excited singlet and triplet electronic states: a quantum mechanical study

2005

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The structures of isotopomers of conformationally flexible acetyl chloride molecule, CH 3 COCl and CD 3 COCl, in the ground (S 0 ) and lowest excited singlet (S 1 ) and triplet (T 1 ) electronic states were calculated by the RHF, MP2, and CASSCF methods. The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these elec tronic states were estimated. According to calculations, electronic excitation causes consider able conformational changes involving rotation of the CH 3 (CD 3 ) top and a substantial devia tion of the CCOCl fragment from planarity. The results of calculations agree with experimental data. Two dimensional torsional inversion sections of the potential energy surface were calcu lated and analyzed. Vibrational problems for large amplitude vibrations (torsional vibration in the S 0 state and both torsional and inversion vibrations in the T 1 and S 1 states) were solved in one and two dimensional approximations.Key words: ab initio quantum chemical calculations, carbonyl compounds, acetyl chloride, isotopomers, vibrational frequencies, potential energy surface, ground electronic state, excited electronic states.Studies on the structures of conformationally flexible molecules in the ground and excited electronic states are of considerable importance from both practical and theo retical standpoints. The structures of stable conformers, the energy differences between them, and the heights of potential barriers to conformational transitions are re sponsible for a number of the most important properties of molecules and compounds. 1-3 These are the electrical and optical properties, thermodynamic characteristics, reactivity and biological activity, mechanisms of chemi cal (including photochemical) reactions, etc. Prediction of the structure and properties of such molecules first of all requires obtaining and accumulation of relevant ex perimental and theoretical data. Besides, of considerable interest is to elucidate (i) the physical nature of the poten tials of internal rotation and inversion and (ii) conforma tional changes accompanying the electronic excitation of molecules (see, e.g., Refs 1-5).It was experimentally established that transitions of certain molecules of carbonyl compounds with symmetri cal CR 3 (R = H, D, F, Cl, CH 3 ) tops from the ground state S 0 to the lowest excited singlet (S 1 ) and triplet (T 1 ) electronic states are accompanied by significant changes in the equilibrium geometric structures, namely, by rota tion of the tops by about 60° and by pyramidalization of carbonyl fragments. 5-11Experimental studies of the structure of conforma tionally flexible molecules (especially if they are in ex cited electronic states) face severe difficulties, which are first of all associated with possible ambiguity of band as signment in the vibronic spectra and instability of inverse problems of the determination of potentials of internal rotation and inversion. Therefore, quantum mechanical calculations can serve as both an additional source of structural ...

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The conformational changes accompanying the triplet–singlet electronic excitation of acetaldehyde, CH₃CHO

Cited by 30 publications

References 8 publications

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

The electronic spectra of acetaldehyde-h₄ and -d₄

Structure of acetyl chloride molecule isotopomers CH3COCl and CD3COCl in the ground and lowest excited singlet and triplet electronic states: a quantum mechanical study

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The conformational changes accompanying the triplet–singlet electronic excitation of acetaldehyde, CH3CHO

Cited by 30 publications

References 8 publications

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

The electronic spectra of acetaldehyde-h4 and -d4

Structure of acetyl chloride molecule isotopomers CH3COCl and CD3COCl in the ground and lowest excited singlet and triplet electronic states: a quantum mechanical study

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The conformational changes accompanying the triplet–singlet electronic excitation of acetaldehyde, CH₃CHO

The electronic spectra of acetaldehyde-h₄ and -d₄