Knowledge Bank

The two photon resonant multiphoton ionization spectrum of expansion cooled toluene was measured at low temperature $(\sim 40\circ K$ ) and medium resolution $(\sim 2cm-1)$. The $A1$ ``forbidden’’ vibronic transitions, analogous to the $A1g$ transitions of benzene, have low temperature contours predictable form the room temperature MPI $spectrum.1,2$ The $B2$ allowed vibronic transitions, including the origin, have quite different contours than in the room temperature MPI spectrum. Heating the vapor (2% toluene in $H2$ or He) before expansion causes further changes in the MPI spectrum, which also differ form that observed at room temperature. These spectra will be discussed. By the time of presentation, it is hoped that analogous measurements will have been carried out on fluorobenzene, a similar, but more completely analyzed molecule than $toluene.2$