The S1 ← S0 vibronic spectra and structure of the (CH3)2 CHCHO and (CH3)2 CHCDO 2-methylpropanal molecules |
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Authors: | I A Godunov S L Lure N N Yakovlev and V A Bataev |
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Institution: | (1) Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992, Russia |
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Abstract: | A multipass cell with an optical path up to 120 m long was used to measure the vibronic absorption spectra of 2-methylpropanal-h1 (MPA-h1, (CH3)2CHCHO)) and 2-methylpropanal-d1 (MPA-d1, (CH3)2CHCDO)) over the frequency range 28200–31600 cm−1. The most intense spectral lines were assigned to transitions from vibrational levels of the cis and gauche MPA-h1 and MPA-d1 conformers in the ground electronic state (S
0) to vibrational levels of conformers 1 and 3 in the lowest singlet excited electronic state (S
1). According to our estimates, the origins (0
0
0
) of the 1
S
1) ← cis(S
0) and 3(S
1) ← cis(S
0) and also 1(S
1) ← gauche(S
0) and 3(S
1) ← gauche(S
0) electronic transitions were situated at 29147 and 29177, 29391 and 29417 cm−1, respectively, for MPA-h1 and at 29226 and 29240, 29480 and 29500 cm−1 for MPA-d1. The structure of conformers 1 and 3 in the S
1 state was shown to differ from the structure of the cis and gauche conformers in the S
0 state by the angle of rotation of the (CH3)2CH-isopropyl top and “pyramidal distortion” of the CCHO/CCDO carbonyl fragment. A series of fundamental frequencies of MPA
conformers in different electronic states were found. The potential functions of inversion were determined for the conformer
1-conformer 3 pairs of MPA-h1 and MPA-d1 from the experimental energy levels of inversion vibrations. The potential barriers to inversion and equilibrium displacements
of the CH/CD bond out of the CCO plane were found to be 735/675 cm−1 and ±34°/±32° for MPA-h1 and MPA-d1, respectively.
Original Russian Text ? I.A. Godunov, S.L. Lur’e, N.N. Yakovlev, V.A. Bataev, 2007, published in Zhurnal Fizicheskoi Khimii,
2007, Vol. 81, No. 1, pp. 52–62. |
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Keywords: | |
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