Ground state atomic terms, low lying excited states, and degeneracies:
The Do values for the cations are negative because they are at higher energy
than the atom. The zero point is chosen as the dissociation limit of the molecules
into atoms. Correspondingly the Do for the ground state atoms is zero.
Do for CO2, NH3, and H2O are from D. A. McQuarrie,
"Statistical Mechanics," Harper and Row, 1976.
The polyatomic spectroscopic constants are from G. Herzberg, "Electronic Spectra and
Electronic Structure of Polyatomic Molecules, V. 4", Van Nostrand, 1945. The diatomic
spectroscopic constants are from M. Karplus, R. N. Porter, "Atoms and Molecules",
W. A. Benjamin, Menlo Park, CA, 1970. Table 7.3.
For the polyatomic molecules only vibration frequencies below 2000 cm-1
are listed (the high energy vibrations don't contribute a significant number of
Colby College, T. W. Shattuck, 5/20/06