Theoretical Calculations on Excited Electronic States of Benzaldehyde and Observation of the S2←S0 Jet-Cooled Spectrum

The S 2 (ππ*)←S 0 spectrum of jet-cooled benzaldehyde has been recorded by laser ionization. The band has been located at 35 191 cm -1 . Ten fundamental vibrations have been assigned following a vibrational analysis assisted by theoretical calculations. Ab initio molecular orbital methods have been used to examine the electronically excited states of benzaldehyde. On π*←n excitation the primary geometric distortions are in the formyl group, while on π*←π excitation these are mainly in the aromatic ring. Vibrational frequencies were found to be in reasonable agreement with the experimental data for the states studied (S 0, S 1 (nπ*), S 2 (ππ*), and T(nπ*)), and the calculations provided a useful guide in assigning the observed excited state fundamentals.