THE MULTIPHOTON IONIZATION SPECTRUM OF PYRAZINE

Abstract

The multiphoton ionization $spectrum^{1}$ of pyrazine has been obtained for dye laser wavelengths of 416 to 360 nm. In the 3 photon ionization region a new two photon resonant state was observed between 49 000 and 56 000 $cm^{-1}$. The origin of the state was at 50 830 $cm^{-1}$. The following Ag modes were vibrationally active: $\nu_{6a}, \nu_{1},$ and $\nu_{8a}$, with $\nu_{6a}$ a strong progression forming mode. This analysis was aided by the observation of ``hot” bands and sequence structure. Comparison of Franck-Condon factors, excited state frequencies, and vibrational activities with the $photo-electron^{2}$ and vacuum $UV^{3}$ spectra indicate that the observed state is a gerade Rydberg state.