CONFORMATIONAL-ANALYSIS OF PROPIONALDEHYDE (PROPANAL) BY 2-PHOTON SPECTROSCOPY OF THE 3S[-N RYDBERG TRANSITION

The two-photon 3s<--n Rydberg spectra of propionaldehyde have been rec orded under cell and free-jet expansion conditions. The occurrence of two separate electronic systems for the cis and disfavoured gauche con formers has been confirmed. In-phase electronic transitions are found in both formyl and methyl torsional coordinates, and the analysis of t orsional sequences has provided new information on conformational pote ntial functions. The eis (n, 3s) conformer is stabilised. the energy g ap between cis and gauche conformers increases to 1260 cm(-1) and the methyl internal rotation barriers increase for both conformers on elec tronic excitation. (C) 1997 Elsevier Science B.V.