jp9624358_si_001.pdf (359.28 kB)
Ab Initio CBS-QCI Calculations of the Inversion Mode of Ammonia
journal contribution
posted on 1997-04-24, 00:00 authored by Daniel J. Rush, Kenneth B. WibergThe complete basis set (CBS) extrapolation model chemistry of
Petersson and co-workers was used to explore
the potential energy surface of the ammonia inversion mode. The
CBS-QCI theoretical energies were calculated
using 41 points along the inversion surface at the MP2/6-311++G**
geometries. A variety of techniques
were explored to model the potential surface. Subsequent numerical
solution of the one-dimensional
Schrödinger equation produced energy levels for ammonia
isotopomers in good agreement with experimental
transitions. Accounting for the variable nature of the reduced
mass with inversion coordinate is shown to be
of significance. This study is an important first step in
producing reliable methods for making ab initio
thermodynamic corrections from ΔE(0 K) to
ΔG(298 K) in other nitrogen-containing systems.
Because no
experimental methods generate data at 0 K, these corrections provide a
crucial link between experimental
thermochemical energies and ab initio theory.