Dimers of aromatic molecules: (Benzene)2, (toluene)2, and benzene–toluene

Abstract

The optical absorption spectra of the first excited singlet states of the benzene, toluene, and toluene–benzene dimers, created in a supersonic molecular jet, are reported. The absorption spectra are detected through two‐color time of flightmass spectroscopy; this method eliminates fragmentation of dimers and higher clusters and the dimer spectra are uniquely observed. The benzene dimer observed in this experiment is suggested to have a parallel stacked and displaced configuration of C 2h symmetry. Both the toluene and toluene–benzene dimers have two configurations: parallel stacked and displaced [based on (benzene)2] and perpendicular. (Benzene)2, (toluene)2, and toluene–benzene form excimers in the excited state for the parallel stacked displaced configurations. The transformation of (benzene)2 to the excimer takes place at the 00 with a ∼0 cm− 1 barrier while the excimer is formed for toluene–benzene with a ∼900 cm− 1 barrier. An exciton analysis of the (benzene)2 00 0 and 61 0 yields M 1 2, the excitation exchange interaction, equal to ∼1.6 cm− 1.