Dynamics of large molecule Van der Waals complexes studied with ZEKE spectroscopy

Abstract

Zero electron kinetic energy (ZEKE) photoelectron spectroscopy has been applied as a probing technique to measure S₁ vibrational dynamics in Van der Waals molecules including the study of intramolecular vibrational energy redistribution (IVR) 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 S₁ origin of each complex, have been measured, yielding the change in binding energy between the neutral and the cation as well as some information on the intermolecular Van der Waals vibrational modes of the cation. Dynamical information on IVR and VP in the S₁ complexes is obtained by delayed pump–probe ZEKE spectroscopy using picosecond and nanosecond laser pulses. The CH₄ complexes are observed to dissociate rapidly in a sequential process of IVR followed by VP. The phenol and aniline argon complexes dissociate much more slowly due to a slow initial IVR process. Toluidine and cresol argon complexes undergo rapid IVR and dissociation similar to the CH₄ complexes. Models of dissociation are discussed as well as the role of the methyl group on the dissociation dynamics.