The Inversion Potential of Ammonia: An Intrinsic Reaction Coordinate Calculation for Student Investigation

Arthur M. Halpern, B. R. Ramachandran, and Eric D. Glendening

Department of Chemistry, Indiana State University, Terre Haute, IN 47809

Abstract

A computational–experimental project is described in which upper-level students construct the double minimum inversion potential for NH₃ from intrinsic reaction coordinate (IRC) calculations using ab initio methods (MP2/cc-pVTZ). They use this potential to obtain the inversion eigenvalues from which they can predict the frequencies of the split inversion mode transitions and make comparisons with experimental results. In an experimental component they acquire the IR spectrum of NH₃ vapor in the 900–1000 cm^-1 region. The results obtained from the calculation are used to estimate the rates of inversion from both tunneling and thermal processes. Suggestions for extensions of this project to other compounds are provided.

Journal of Chemical Education 2007, 84, 1067                   Full Text (PDF)

-- ThanhTruong - 11 Jul 2007