The S 1 ← S 0 vibronic spectra and structure of the (CH3)2 CHCHO and (CH3)2 CHCDO 2-methylpropanal molecules.

Autor: Godunov, I., Lur’e, S., Yakovlev, N., Bataev, V.
Zdroj: Russian Journal of Physical Chemistry; Jan2007, Vol. 81 Issue 1, p47-57, 11p
Abstrakt: 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) 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. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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