Two-photon ionization studies of binary aromatic van der Waals clusters: Benzene...chlorobenzene and (chlorobenzene)₂

Jet-cooled van der Waals dimers of benzene (B) and chlorobenzene (BCl) were studied by one-color resonant two-photon ionization through the S_o→S₁ transition of the chlorobenzene. The spectra of BCl...B and (BCl)₂ in the 0-0 band both show two main features with different spectral shifts. These two main features are attributed to two different geometries: perpendicular T-shaped geometry and parallel displaced geometry. This assignment is supported by the relative intensity dependence on the internal temperature and our ab initio calculations at the MP2 level. The binding energies of BCl...B and (BCl)₂ were measured near the two-photon ionization dissociation threshold in a reflectron time-of-flight mass spectrometer (RTOF/MS). Our estimated binding energies of BCl...B and BCl...BCl are 0.14±0.01 eV and 0.15±0.01 eV, respectively, consistent with their increasing dipole moment and polarizability in that order.