PROBING POTENTIAL-ENERGY SURFACES VIA HIGH-RESOLUTION IR LASER SPECTROSCOPY

The 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 collision dynamics, intermolecular forces and intramolecular energy flow. As a particular focus of this talk, direct absorption methods in combination with slit supersonic expansions and crossed molecular beams offer an extremely general tool for probing unimolecular and bimolecular dynamics with full quantum-state resolution. In this lecture, results from our laboratory are presented in four areas. (1) Near-IR spectroscopic studies of multiple rare-gas cluster species such as Ar-n-HF and Ar-n-DF (n = 1, 2, 3 and 4) are discussed which elucidate the role of pairwise and non-pairwise additive (i.e. multibody) effects on minimum-energy structures, 'solvent'-induced vibrational red shifts and Van der Waals intermolecular modes of the clusters. (2) A systematic investigation of vibrational frequencies, tunnelling dynamics and predissociation lifetimes for all four intermolecular modes in HF and DF dimers is described, which provides demanding tests of potential-energy surfaces for this prototypical hydrogen-bonded complex. (3) Results are presented from a high-resolution near-IR technique for state-to-state scattering in molecular beams, which probes the repulsive inner wall anisotropy at energies above the dissociation limit. (4) Finally, a new method is described for UV photochemical reaction dynamics in state-selected clusters, which exploits high-resolution (Delta nu less than or similar to 0.005 cm(-1)) overtone excitation to pre-excite specific quantum states in weakly bound species such as Ar-H2O.