Positive charge distributio in (benzene)_1 (toleune)_2~+ and (benzene)_2(toluene)_1~+ studied by photodissociation spectroscopy

摘要

The positive charge distribution in benzene-=toluene heterotrimer ions is investigated by photodissociation spectroscopy in the near-infrared (6000-14 000 cm~(-1)) and infrared (2800-3150 cm~(-1)) regions. The electronic spectra of (benzene)_1(toluene)_2~+ and (benzene)_2(toluene)_1~+ in the near-infrared region display a strong band at 9430 and 8330 cm~(-1), respectively. These bands are ascribed to the charge resonance band; the positive charge is not localized on a single molecule. The vibrational spectrum of (benzene)_1(toluene-d_8)_2~+ shows three distinct bands at 3054, 3084, and 3108 cm~(-1); these bands are assigned to the CH stretching vibrations of the benzene moiety. The molecule in the (benzene)_1(toluene)_2~+ ion has a neutral character. The positive charge is localized on the toluene dimer unit with a structure writen as (toluene)_2~+…(benzene)_1. The vibrational spectrum of (benzene-d_6)_2(toluene)_1~+ shows dissimilar features to the spectrum of the neutral toluene monomer, suggesting that a certain amount of the positive charge is carried by the toluene moiety. These results are explained by the charge resonance interaction between (benzene)_2 and (toluene)_1. A simple perturbatio theory is applied for determining the positive charge distribution in (benzene)_2(toluene)_1~+. The probability of finding the charge on the (benzene)_2 and (toluene)_1 moieties is analyzed to be 58% and 42%, respectively.