Properties of activation barriers from thermal rate data on forward and reverse reactions: hydroxyl + hydrogen, amidogen + hydrogen, methyl + hydrogen and methyl + hydrogen chloride

Abstract

Experimental data on the temperature dependence of forward and reverse transfers of hydrogen atoms have been assembled. The following transition-state theory (TST) expressions, incorporating a factor, {kappa}, for tunneling through a one-dimensional Eckart barrier of effective forward and reverse heights E{sub f} and E{sub r} and of characteristic tunneling temperature, T*, were fitted by least-squares methods to the data for each reaction. For the reactions OH + H{sub 2} {r equilibrium} H{sub 2}O + H and NH{sub 2} + H{sub 2} {r equilibrium} NH{sub 3} + H, most standard deviations are from 1% to 3% of the parameter values and the parameters agree well with independent quantum chemical or thermochemical estimates. For the reactions CH{sub 3} + H{sub 2} {r equilibrium} CH{sub 4} + H, E{sub f} - E{sub r} disagrees with the values from the thermochemical tables, suggesting that there are errors in these tables or errors of 1 order of magnitude in the low-temperature rate constants.