RESONANT 2-PHOTON IONIZATION SPECTRA OF THE EXTERNAL VIBRATIONAL-MODES OF THE CHLOROBENZENE, PHENOL, AND TOLUENE RARE-GAS (NE, AR, KR, XE) VANDERWAALS COMPLEXES

Using resonant two-photon ionization and time-of-flight mass spectrometry techniques, original spectra of the external vibrational modes often van der Waals (vdW) complexes are presented. The complexes are formed in a pulsed supersonic expansion between a rare gas atom (Ne, Ar, Kr, Xe) and a monosubstituted benzene derivative chlorobenzene, phenol, or toluene. For each complex, the red shift of the S1 ← S0 0 00 energy due to complexation, and the vdW stretching and bending frequencies are determined. In some cases, the bending mode anharmonicity and Fermi resonances could be analyzed from the extended progressions observed for the bending vibration. The diatomic model is used to estimate the stretching force constant. Intensity, mass, and dissymmetry effects induced by the X substituent on the benzene ring are analyzed. In particular, in these Cs symmetry complexes, every bending A′ level is observed, not just the even bending levels found in C6v or C 2v complexes. Finally, some correlations are shown from the comparison of the present results with the few available data of the literature. © 1990 American Institute of Physics.