Comment on the isotope dependence of transmission coefficients

The results of quantum-dynamical computations for the isotopic analogues of the chemical reaction H + H₂ →H₂ + H and experiment for the analogues of the F + H₂ →HF + H reaction are examined to determine if there exists isotopic invariance relations. A theorem due to Kuntz et al. is shown to imply the invariance of the transmission coefficient in classical systems when all masses are scaled by a common factor. The theorem is found to be approximately satisfied for quantal systems. Isotopic invariance of the surprisal associated with energy disposal for systems under the same mass scaling is shown to be another consequence of the theorem. Evidence for additional invariance relations, even when the masses are not scaled by the same factor, is presented. Of particular interest is the invariant representation of the detailed (state-to-state) transmission coefficients.