Zero Kinetic Energy (ZEKE) Photoelectron Spectroscopic Study of Thioanisole and Its van der Waals Complexes with Argon

Abstract

Two-color zero kinetic energy (ZEKE) photoelectron spectra due to the cation D0 states of thioanisole and its van der Waals complexes with argon (thioanisole−Ar and −Ar2) in a supersonic jet are reported for the first time, together with mass-selected REMPI (resonantly enhanced multiphoton ionization) spectra associated with their S1 states. For bare thioanisole, the adiabatic ionization energy (Ia) is 63 906 ± 3 cm-1 and the S1 origin is located at 34 506 ± 1 cm-1. Low-frequency vibrational progressions due to the excitation of the CH3S torsion (94 cm-1) are observed in the ZEKE photoelectron spectra. A series 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 torsional barrier of 530 cm-1 along the S−C(sp2) bond and a minimum energy for the CH3 group rotated 90° from the aromatic plane. Intensive Δv = 0 ionization transitions are observed in the ZEKE pho...