Russell D. Johnson III and Karl K. Irikura |
Research Opportunity Number 50.83.81.B1676
|
This research focuses on the calculation of anharmonic vibrational energy
levels for polyatomic molecules. The goal is to obtain accurate energy
levels for the prediction of spectroscopic properties and thermodynamic
quantities, such as entropy and enthalpy. The vibrations for most stable
species can be treated as separable and as harmonic oscillators; however,
for some molecules, this does not work. Examples of ill-behaved vibrations
include low-frequency or "soft" modes, inversion or rotation barriers that
are comparable to room temperature, and coupled vibrational modes. The
main issues are (1) to find the appropriate ab initio theory level
for generating the multidimensional potential energy surface and (2) to
explore methods for computing the vibrational energy levels, such as variational,
perturbational, and self-consistent field theories.