AN IMPROVED POTENTIAL-ENERGY SURFACE FOR THE H2CL SYSTEM AND ITS USE FOR CALCULATIONS OF RATE COEFFICIENTS AND KINETIC ISOTOPE EFFECTS

We present a new potential energy surface (called G3) for the chemical reaction Cl + H-2 --> HCl + H. The new surface is based on a previous potential surface called GQQ, and it incorporates an improved bending potential that is fit to the results of nb initio electronic structur e calculations. Calculations based on variational transition state the ory with semiclassical transmission coefficients corresponding to an o ptimized multidimensional tunneling treatment (VTST/OMT, in particular improved canonical variational theory with least-action ground-state transmission coefficients) are carried out for nine different isotopom eric versions of the abstraction reaction and six different isotopomer ic versions of the exchange reaction involving the H, D, and T isotope s of hydrogen, and the new surface is tested by comparing these calcul ations to available experimental data. The theoretical data are also u sed to investigate the equilibrium constant and the branching ratio fo r the reverse reaction, and calculations of these quantities are compa red to the available experimental and theoretical data.