Observation of van der Waals vibrations in zero kinetic energy (ZEKE) photoelectron spectra of toluene-Ar van der Waals complex

Zero kinetic energy (ZEKE) photoelectron spectra due to van der Waals (vdW) vibrations have been observed for the toluene-Ar vdW complex in a supersonic free jet. ZEKE photoelectron measurements were carried out by using two-color (1 + 1') resonant excitation followed by pulsed-field ionization (PFI). The first laser was tuned to the S-1 origin and its several specific vdW vibrational levels, while the second laser was scanned to observe a very low frequency vdW vibrational structure in the cation ground state (D-0). From ZEKE photoelectron spectra thus obtained via several S-1 vdW vibrational levels, we have been able to identify the non-totally symmetric vdW bending mode (b(x)(+): 17 cm(-1)) and the vdW stretching mode (s(z)(+): 49 cm(-1)) for the toluene-Ar cation for the first time. (C) 1998 Elsevier Science B.V.