The photoabsorption and Constant Ion State Spectroscopy of Vinyl Bromide.

In this paper we report the photoabsorption and the constant ion state spectroscopy of vinyl bromide (C2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in detail between 5.0 and 12.0 eV photon energy revealing many previously unobserved structures. These features were analyzed in terms of valence to virtual valence transitions and Rydberg series. The examination of the three Rydberg series converging towards the first ionization threshold (2a"->ns, 2a"->np and 2a"->nd) leads to wavenumbers of 335+/-30, 690+/-30 and 1305+/-30 cm-1. The vibrational wavenumbers of the progressions belonging to Rydberg series converging towards the second ionization threshold are 485+/-30 and 1145+/-50 cm-1. Ab initio calculations helped the assignment of the valence transitions and of the observed vibrational wave numbers in the Rydberg series.
Constant Ionic State spectra were recorded for vibronic states corresponding to the first and the second electronic states of the ion. Their fine structures are assigned to the autoionization of Rydberg states. The autoionization decay of these Rydberg states is analyzed qualitatively in terms of the vibrational nature of the final ionic state.