A Semiclassical Study of Tunneling Effects in Aziridine

Report No. ARL-TR-2124
Authors: Guo, Yin; Wilson, Angela K.; Chabalowski, Cary F.; Thompson, Donald L.
Date/Pages: November 1999; 31 pages
Abstract: The tunneling effects in the molecular inversion of aziridine are investigated. A full-dimensional potential was constructed based on ab initio results and used to study the effect of vibrational excitations on tunneling. Using the semiclassical approach that incorporates tunneling into classical trajectory calculations, it is found that excitations of all the modes except the reaction coordinate have negligible effects on tunneling. This allows accurate thermal-rate calculations carried out by using a one-dimensional (l-D) model. (This is in accord with the conclusions of the work by N. Rom, V. Ryaboy, and N. Moiseyev Chemical Physics Letters, vol. 204, p. 175, 1993 and by Z. Smedarchina, W. Siebrand, and M. Z. Zgierski Journal of Chemical Physics, vol. 102, p. 7024, 1995.) A l-D Weutzel- Kramers-Brillouin (WKB) formula was employed to obtain the level splitting and was found to be very accurate based on comparisons with the quantum results. Furthermore, the calculated thermal rates are in good agreement with the experimentally measured values. The results provide insight into the reaction mechanism and explanations for the experimental findings of non-Rice-Ramsperger-Kassel-Marcus (RRKM) behavior and incoherent tunneling.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 1999