Weak interaction in benzene clusters

Abstract

Experiments with supersonic jets have been performed to prepare clusters of benzene molecules. The spectra of the simultaneously prepared clusters of different size are influenced by the various low-frequency van der Waals modes. The spectra are still more complicated from different conformers, which increase dramatically the number of lines, even for only a few modes. Even two van der Waals modes, together with site splitting and exciton interaction, give rise to 20 transitions in a 10 wavenumber interval at 60 cm–1 excess energy if one 13C atom is in one of the benzene rings. Individually sized cluster spectra are measured with ion detection after ionization with a second laser. To discriminate against influences from dissociation of larger clusters different experiments have been performed which vary the excess energy on ionization or subtract simultaneously obtained spectra with detection of different masses, which leads to clean spectra and gives information on the different dissociation channels involved. The dissociation of clusters leads to severe problems when determining ionization potentials. With a new method of kinetic-energy discrimination unwanted contributions from the decay of larger clusters can be eliminated.