Tunnel Effects in the H + D2 and D + H2 Reactions

摘要

We considered the tunneling effect on the rate constants calculated from transition-state theory for the H + D2 and D + H2 reactions. A method for evaluating the important parameter Ec (potential barrier height) was proposed. A tunnel-effect correlation factor (TECF) ッtexp ヨt was estimated from experimental data, and compared with the corresponding values obtained from many theoretical methods. According to our results, the tunneling effect cannot be negligible around 800。 K where the TECF value is ca. 0.8 whereas the factor approaches to unity at T > 2400。K where the tunneling completely disappears. In addition to the above fact, we also found that the TECF for the D + H2 reaction is greater than that of the H + D2 reaction in agreement with Garrett and Truhlar`s result. In contrast to our result, however, Shavitt found that the order is reversed, i.e., TECF for (D + H2) is greater than that for (H + D2). We discussed about the Shavitt`s result.