Molecule Types <Prev Next>

Vibrational Structure

PGOPHER has can do two significant types of calculations involving vibrations:

  1. Vibronic energy levels, and the pattern of vibrational transitions associated with an electronic transition. If an l matrix is available for the states involved, then full multidimensional Franck-Condon factors can be calculated, but simpler empirical approaches can be taken if this is not available.
  2. A force field analysis, calculating vibrational frequencies, l matrix, isotope shifts, rotational constants, centrifugal distortion constants and Coriolis coupling constants from the force constants and geometry of the molecule.
The force field calculation can feed directly into calculating vibronic energy levels and transitions, or either mode can be used in a stand alone manner. Either (or both) calculation can be worked backwards to fit observed values to molecular parameters. Both modes can use ab initio calculations as a starting point, and even low quality ab initio calculations can give a useful starting point for analysis. A typical use case might involve an ab initio calculation of the force field or other parameters, which is then adjusted or refined to experimental observation or other criteria.

To start, work through the worked examples below.

Vibrational Energy Levels and Franck-Condon Factors

Force Field Analysis