Resolution IR Laser Studies of Molecular Clusters: Walking the Line Between Spectroscopy and Dynamics

Author Institution: "National Institute for Standards and Technology, University of Colorado", Boulder, ColoradoThe use of high resolution IR lasers for spectroscopic detection and characterization of trace, weakly bound cluster species in low density, jet cooled environments has led to enormous progress in the study of intermolecular potentials, collision dynamics and intramolecular energy flow. As this talk will hope to elucidate, the further combination of such near-IR spectroscopies with slit supersonic expansions, crossed molecular beams, and vibrationally mediated photodissociation provide a particularly general tool for probing unimolecular and bimolecular dynamics with full quantum state resolution. This talk will present results from our laboratory in following areas. First of all, we will focus on a high resolution investigation of the HF dimer potential energy surface, exploiting near-IR combination bands to probe vibrational frequencies, tunnelling dynamics and predissociation lifetimes for all four intermolecular modes in both HF and DF dimers. Secondly, direct absorption methods have developed sufficient sensitivity to permit study of larger clusters such as trimers, tetramers, and pentamers with rotational resolution; results will be presented which elucidate the role of multibody effects on minimum energy structures, ``solvent'' induced vibrational red shifts, and van der Waals intermolecular modes. Thirdly, we discuss a high resolution near-IR technique for state-to-state scattering in molecular beams, which, quite complementary to spectroscopy of the corresponding clusters, begins to probe the potential surface at energies above the dissociation limit. Time permitting, results from a new double resonance method for probing photophysical and photochemical reaction dynamics in state- and size-selected clusters will be presented