Photoelectron spectroscopy of vinylbromide and intramolecular dynamics of the ionic B̃ state Original Research Article

In this paper, we report the He(I) photoelectron spectrum (PES) and the threshold-photoelectron (TPES) spectrum of C2H3Br. The fine structure observed in the first two ionic states in the He(I) spectrum is assigned to progressions belonging partially to previously unobserved vibrational normal modes. The TPES has been measured between 9.0 and 25.0 eV, and the photon energy range of 9.8–12.0 eV has been investigated in more detail. Extensive calculations with the gaussian set of programs have been performed to help in the assignment of the observed features. Furthermore, a conical intersection between the à 2A′′ and the B̃ 2A″ states was found to take place along the C–Br stretching coordinate. Intramolecular dynamics of the B̃ 2A′′ state, initially prepared in the Frank–Condon region, was probed by the Fourier transform of the spectrum. The B̃ 2A′′ state is almost readily depleted, most probably due to a very effective internal conversion through the conical intersection.