The T1 ← S0 vibronic spectrum and the structure of the 2,2-difluoroethanal molecule in the T1 state

The vibronic absorption spectrum of 2,2-difluoroethanal (CHF2CHO) vapor was obtained in a multipass cell with a large optical path (up to 140 m). The spectrum in the region 355-392 nm was assigned to the T-1 <-- S-0 electronic transition from the ground S-0 to the first excited triplet T-1 state. The vibrational structure of the spectrum was studied. The spectral bands were assigned to two vibronic transition systems, between cis conformer (S-0) vibrational levels and conformers I and III (T-1) with the origins (0(0)(0) transitions) at 26830 and 26660 cm(-1), respectively. Excitation of the cis conformer was shown to cause top rotation and a pyramidal distortion of the carbonyl fragment. Several fundamental frequencies, in particular, torsional and inversion energy levels, were found for conformers I and III. The experimental data were on the whole in satisfactory agreement with the results of quantum-mechanical calculations of the 2,2-difluoroethanal molecule in the S-0 and T-1 states.