Theoretical rate constants: on the error cancellation using conventional transition-state theory and Wigner's tunnelling correction

Abstract The rate constants of three hydrogen abstraction reactions NH 3 + OH → NH 2 + H 2 O, H 2 + OH → H + H 2 O and HNO + H → H 2 + NO, were calculated by means of conventional transition-state theory combined with Wigner's tunnelling effect at low temperature. Using large basis sets, wavefunctions that are eigenstates of the S 2 operator, an empirical post-fourth-order Moller-Plessett correction and a correct description of the imaginary frequency at the saddle point, one finds good agreement with the experimental kinetic data, possibly through a fortuitous cancellation of opposing effects.