ZERO KINETIC-ENERGY (ZEKE) PHOTOELECTRON SPECTROSCOPIC STUDY OF THIOANISOLE AND ITS VAN-DER-WAALS COMPLEXES WITH ARGON

Two-color zero kinetic energy (ZEKE) photoelectron spectra due to the cation D-0 states of thioanisole and its van der Waals complexes with argon (thioanisole-Ar and -Ar-2) in a supersonic jet are reported for the first time, together with mass-selected REMPI (resonantly enhanced multiphoton ionization) spectra associated with their S-1 states. For bare thioanisole, the adiabatic ionization energy (I-a) is 63 906 +/- 3 cm(-1) and the S-1 origin is located at 34 506 +/- 1 cm(-1). Low-fr equency vibrational progressions due to the excitation of the CH3S tor sion (94 cm(-1)) are observed in the ZEKE photoelectron spectra. A ser ies of hot bands showing a large anharmonicity is observed in a REMPI spectrum, indicating that the CH3S torsional frequency is 68 cm(-1) in the neutral ground state. An ab initio 6-311G* calculation gives a t orsional barrier of 530 cm(-1) along the S-C(sp(2)) bond and a minimum energy for the CH3 group rotated 90 degrees from the aromatic plane. Intensive Delta v = 0 ionization transitions are observed in the ZEKE photoelectron spectra via several S-1 vibronic levels. Concerning the thioanisole-Ar and -Ar-2 vdW complexes, the shifts in I-a amount to -1 17 and -231 cm(-1), respectively, with respect to thioanisole, while t he shifts in the S-1 origin are -51 and -100 cm(-1) respectively. The vdW bending modes (b(x) and b(y)) in the S-1 states are resolved in th e REMPI spectrum. The vdW b(x) mode is observed up to v = 5 in the ZEK E photoelectron spectrum due to thioanisole-Ar.