			15min:

EXPERIMENTAL DETERMINATION OF GROUND STATE BINDING ENERGIES IN HETERO- AND HOMONUCLEAR RARE GAS-DIHALOGEN COMPLEXES.

DAVID S. BOUCHER, DAVID B. STRASFELD, JOSHUA P. DARR, RICHARD A. LOOMIS, Department of Chemistry, Washington University, One Brookings Drive, CB 1134, Saint Louis, MO 63130; JOHN M. HERBERT, Department of Chemistry, University of California, Berkeley, CA 94720; ANNE B. MCCOY, Department of Chemistry, The Ohio State University, Columbus, OH 43210.

A simple Arrhenius model based on the assumptions of a thermodynamic equilibrium between the T-shaped and linear isomers of the He cdots I³⁵Cl( X , v ''=0) rare gas-heteronuclear dihalogen complex and of a Boltzmann rotational distribution for each isomer is used to find the relative binding energies of the isomers. The model was tested by comparing the intensities of the T-shaped and linear bands observed in laser-induced fluorescence spectra recorded in the ICl B - X , 3-0 spectral region in varying temperature regions in the expansion. The results reveal that the T-shaped isomer is 3.2(1.0) cm^-1 higher in energy than the linear isomer. Using two-laser, pump-probe and high-resolution action spectroscopy the linear binding energy was precisely determined to be 21.97(12) cm^-1, thereby indicating a T-shaped He cdots I³⁵Cl( X , v ''=0) binding energy of 18.8(1.0) cm^-1. The approach was then extended to the He cdots ⁷⁹Br₂( X , v ''=0) rare gas-homonuclear dihalogen complexes. The intensities of the features associated with transitions of the T-shaped and linear isomers observed in the ro-vibronic spectra recorded in the Br₂ B - X , 11-0 region are used to monitor changes in the relative populations of the isomers. The T-shaped He cdots ⁷⁹Br₂ isomer is found to be only 0.7(2) cm^-1 higher in energy than the linear isomer. Action spectra reveal that the ground state linear isomer is bound by 17.6(4) cm^-1, and thus a binding energy of 16.9(4) cm^-1 for the T-shaped isomer is determined. The experimental energies agree remarkably well with those obtained using a two-dimensional He + Br₂( X , v ''=0) ab initio potential energy surface,17.4 and 16.6 cm^-1 for the linear and T-shaped isomers, respectively.