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

The use of high-resolution IR lasers for spectroscopic detection and c haracterization 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 fl ow. As a particular focus of this talk, direct absorption methods in c ombination with slit supersonic expansions and crossed molecular beams offer an extremely general tool for probing unimolecular and bimolecu lar dynamics with full quantum-state resolution. In this lecture, resu lts from our laboratory are presented in four areas. (1) Near-IR spect roscopic 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 min imum-energy structures, 'solvent'-induced vibrational red shifts and V an der Waals intermolecular modes of the clusters. (2) A systematic in vestigation of vibrational frequencies, tunnelling dynamics and predis sociation lifetimes for all four intermolecular modes in HF and DF dim ers is described, which provides demanding tests of potential-energy s urfaces 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 ne w 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.