The S sub(1) arrow left S sub(0) fluorescence excitation spectrum and structure of propanal in the S sub(1) excited electronic state

• Published in: Physical chemistry chemical physics : PCCP Vol. 18; no. 22; pp. 15244 - 15250
• Main Authors: Godunov, IA, Yakovlev, N N, Terentiev, R V, Maslov, D V, Abramenkov, A V
• Format: Journal Article
• Language: English
• Published: 01.06.2016
• Subjects: Band theory; Electron states; Excitation; Excitation spectra; Fluorescence; Fragments; Inversions; Vibration
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c6cp02138g

We have obtained and analyzed the S sub(1) arrow left S sub(0) fluorescence excitation spectra of jet-cooled propanal-h sub(1) (CH sub(3)CH sub(2)CHO) and -d sub(1) (CH sub(3)CH sub(2)CDO). Using the results of theoretical studies of the structure of propanal molecule in the S sub(1) lowest excited singlet electronic state, we have assigned the bands of both spectra to the vibronic transitions of the cisconformer (in the S sub(0) ground electronic state) to the 1 and 3 conformers (in the S sub(1) state) differed by the angle of the C sub(2)H sub(5) ethyl group rotation around the central C-C bond. The origins of the 1 arrow left cisand 3 arrow left ciselectronic transitions have been observed at 29 997 and 30 075 cm super(-1) for propanal-h sub(1) and at 30 040 and 30 115 cm super(-1) for propanal-d sub(1), respectively. The high activity of torsional (C sub(2)H sub(5) ethyl groups) and inversional (CCHO/CCDO carbonyl fragments) vibrations and the intensity distribution of the bands in torsional sequences (passing through maximum) are in agreement with the theoretical prediction that the S sub(1) arrow left S sub(0) electronic excitation of the cisconformer causes (after geometrical relaxation) the pyramidalization of carbonyl fragments and the rotation of ethyl groups around the central C-C bond. A number of energy levels have been found for torsional and inversional vibrations, and also fundamentals of nu sub(10) (CCO bend) and nu sub(13) (CCC bend) for the both 1 and 3 conformers of propanal-h sub(1) and -d sub(1) have been found. Then the "experimental" potential functions of inversion for the pair of the 1 and 3 conformers have been determined. The heights of potential barriers to inversion and the angle values corresponding to the minima of potential functions of inversion are 900 cm super(-1) and 35 degree for propanal-h sub(1) and 820 cm super(-1) and 34 degree for propanal-d sub(1), respectively.