S1?S0 vibronic spectra and the vapor-state molecular structure of propanal and 2-methylpropanal

Abstract

The vapor-state absorption spectra have been recorded for propanal PA and 2-methylpropanal MP with path lengths up to 120 m. The initial points in the S1←S0 electronic transitions have been identified together with various fundamental vibrational frequencies of the PA and MP conformers. They contain nonplanar aldehyde groups in the S1 states with inversion potential barriers of about 600 cm−1. The parameters of the internal-rotation potential functions in the S1 states have been determined, and the corresponding potential functions in the S0 states have been refined.