DYNAMICS OF LARGE MOLECULE VAN-DER-WAALS COMPLEXES STUDIED WITH ZEKE SPECTROSCOPY

Zero electron kinetic energy (ZEKE) photoelectron spectroscopy has bee n applied as a probing technique to measure S-1 vibrational dynamics i n Van der Waals molecules including the study of intramolecular vibrat ional energy redistribution (TVR) and vibrational predissociation (VP) . The molecular species studied were aniline, p-toluidine, phenol and p-cresol bound to argon and methane. The ZEKE spectra, pumping through the S-1 origin of each complex, have been measured, yielding the chan ge in binding energy between the neutral and the cation as well as som e information on the intermolecular Van der Waals vibrational modes of the cation. Dynamical information on IVR and VP in the S-1 complexes is obtained by delayed pump-probe ZEKE spectroscopy using picosecond a nd nanosecond laser pulses. The CH4 complexes are observed to dissocia te rapidly in a sequential process of IVR followed by VP. The phenol a nd aniline argon complexes dissociate much more slowly due to a slow i nitial IVR process. Toluidine and cresol argon complexes undergo rapid IVR and dissociation similar to the CH4 complexes. Models of dissocia tion are discussed as well as the role of the methyl group on the diss ociation dynamics.