Spectroscopy of large molecular complexes in supersonic jets

In this paper we report the results of an experimental study of laser-induced fluorescence spectroscopy of M·X_n van der Waals complexes, consisting of medium-sized molecules (X=methane, carbon tetrachloride, ammonia, water, methanol, acetonitrile, benzene, and toluene) bound to a large aromatic molecule (M=tetracene and fluorene). These large complexes were synthesized in pulsed supersonic jets of He seeded with M and X. The spectral features assigned to S₀→S₁ electronic-vibrational excitations of these large M·X₁ complexes, which are characterized by narrow linewidths (FWHM) of 2-4 cm ^-1, were attributed to three distinct categories: (i) A vibrationless excitation of M·X₁, (ii) vibrational excitations of M in M·X₁, and (iii) excitations of the vibrations involving relative motion of M and X in the M·X₁ complex.