A quantum reactive scattering study of Mu+H2→MuH+H

Abstract

The results of quantum coupled states (CS) reactive scattering calculations on the reaction Mu+H₂→MuH+H are presented and used to determine reactive cross sections and rate constants. The potential surface used is the chemically accurate Liu–Siegbahn–Truhlar–Horowitz surface, and the calculations are believed to be accurate to about 30%. The reaction probabilities show threshold shifts relative to collinear exact probabilities which are consistent with bending zero point energy effects. Likewise, the cross section thresholds are shifted relative to H+H₂ cross sections by amounts which can be correlated with adiabatic barrier zero point energies. The resulting thermal rate constants are in excellent agreement with experiment (within the experimental error bars at all but one temperature between 608 and 845 K) and the corresponding activation energies agree to within 0.8 kcal/mol. The CS rate constants are also found to agree very well at high temperatures with variational transition state theory rate constants (ICVT/LAG based on WKB adiabatic potentials), with differences of 0% at 875 K and 31% at 608 K. However, the ICVT/LAG rate constants are too low at lower temperatures (by a factor of 3.8 at 300 K). Quasiclassical trajectory rate constants are found to be in error by orders of magnitude if applied in the standard (forward) direction, but are off by less than a factor of 2 when applied in the reverse direction. The overall good agreement of CS with experiment indicates the adequacy of the LSTH potential surface for a reaction where the bottleneck is well into the product channel region and at relatively high energy.