Exact quantum and vibrationally adiabatic quantum, semiclassical and quasiclassical study of the collinear reactions Cl + MuCl, Cl + HCl, Cl + DCl

Abstract

Accurate quantum calculations of reaction probabilities have been carried out using Delves' polar coordinates for the collinear reactions Cl + XCl(ν) →ClX(ν′) + Cl (X = Mu, H, D). An extended London-Eyring-Polanyi-Sato potential energy surface with a linear symmetric barrier height of 35·77 kJ mol^-1 has been used in the calculations. The diagonal ν →ν reaction probabilities dominate over the off-diagonal ν →ν′ ≠ ν reaction probabilities and show sinusoidal oscillations as a function of energy. Superimposed on these oscillations for X = H, D is a spectrum of narrow resonances. The positions of the resonances can be predicted very accurately from the solution of a vibrationally adiabatic (VA) single channel Schrödinger equation provided the diagonal corrections to the VA potential are also included. The sinusoidal oscillations are analysed using VA semiclassical and quasiclassical theories. There is good agreement between the quantum, semiclassical and quasiclassical results at low energies, but differences appear at high energies where the VA assumption starts to break down. The VA approximation is more accurate the lighter the mass of the central atom, that is, its validity increases in the order D<H<Mu.