Intermolecular interactions of carbonyl-containing molecules studied through theirvan der Waals complexes

Experimental and theoretical studies of carbonyl-containing molecule-Ar vdW complexes are recounted and results are interpreted in order to map out the corresponding intermolecular potentials as a function of the relative positions of the two constituents. An intermolecular potential for glyoxal-Ar is formulated by fitting pair potentials with angularly dependent terms to experimentally-based intermolecular potentials with atom-atom interactions similar to those found in glyoxal-Ar, namely the CO$\sb2$-Ar and H$\sb2$-Ar intermolecular potentials. The resulting potential predicts the experimentally determined geometries and corresponding binding energies of all three isomers of glyoxal-Ar, unlike potentials containing only spherical terms. Laser-induced fluorescence (LIF) and holeburning spectroscopy are employed to determine the X and A state geometries of propynal-Ar. This complex is also found to possess more than one stable isomer. Fluorescence traces are fitted in order to determine the quenching rates of different excited state levels, reflecting the Ar orientation dependence of intersystem crossing (ISC) for propynal-Ar. Lastly, degenerate four-wave mixing (DFWM) is proposed as an alternative method to LIF for characterization of vdW complexes, particularly when fluorescence quantum yields are low. Glyoxal dimer is successfully detected and characterized with DFWM