ZEKE PHOTOELECTRON-SPECTRA OF TRANS-STILBENE IN THE S-1 STATE

Measurements of zero kinetic energy (ZEKE) photoelectron spectra were carried out with nanosecond lasers for trans-stilbene in a free jet expansion, by means of two-color (1 + 1') REMPI via several S-1 vibrational levels. A series of observed ZEKE photoelectron spectra of trans-stilbene show well-resolved low-frequency vibrational structure due to the cation in the energy region up to 1500 cm(-1). The adiabatic ionization potential of trans-stilbene has been determined as 61 748 +/- 4 cm(-1). Vibrational frequencies of 290, 208, 49, and 39 cm(-1) have been assigned to the vibrational modes 24(+), 25(+), 36(+), and 37(+) of the cation, respectively. It has also been found that the observed congested vibrational bands originate not only from the initially prepared S-1 levels but also from relaxed S-1 vibrational levels produced by intramolecular vibrational redistribution (IVR). The present IVR results are consistent with an available picosecond laser dispersed fluorescence study. The present work also clearly demonstrates that (1 + 1') ZEKE photoelectron spectroscopy has sufficient capability for studying the dynamics of electronically excited neutral molecules.