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S.Sato,T.Kojima,K.Byodo,H.Shinohara,S.Yanagihara,K.Kimura Van der Waals (vdW) complexes of a series of alkylbenzenes (benzene, toluene, ethylbenzene, and n-propylbenzene) formed with Ar in supersonic jets have been studied with two-color zero-kinetic-energy (ZEKE) electron spectroscopy combined with a PFI (pulsed field ionization) method. The shifts in adiabatic ionization energies (Ia) due to complex formation have been determined as |128 and |112 cm|1 for ethylbenzene|Ar and n-propylbenzene|Ar, respectively, with respect to the bare molecules. These shifts have been reproduced qualitatively in terms of atom|atom Lennard|Jones (LJ) potentials incorporating charge|charge-induced-dipole interactions. Some low-frequency ZEKE bands due to vdW vibrations have been observed for benzene|Ar for the first time. However, no vdW vibrational structures appear in ZEKE electron spectra both for ethylbenzene|Ar and n-propylbenzene|Ar. The absence of vdW vibrational structure in the spectra may be probably due to a steric hindrance between Ar and the alkyl group. This has been supported also by the present LJ potential calculations. Furthermore, for toluene|Ar, it has been found that upon ionization the relative position of Ar is shifted along the direction of the C|C(H3) bond. DOI:10.1016/S0368-2048(00)00218-8 |