Example Polyatomic Molecules

Click on the button to transfer the constants.
Ae/cm-1 Be/cm-1 Ce/cm-1sym no. vo/cm-1 g (electronic)Do/eV

Ground state atomic terms, low lying excited states, and degeneracies:
Element H B C N O F P S Cl Br
Term Symbol 2S1/2 2P1/2 3P0 4S3/2 3P2 2P3/2 4S3/2 3P2 2P3/2 2P3/2
Ground state degeneracy, g 2 2 1 4 5 4 4 5 4 4
Excited state E(cm-1), degeneracy 15.254, 4 16.4, 3 158.5, 3 404, 2 396.8, 3 881, 2
Excited state E(cm-1), degeneracy 43.5, 5 226.1, 1 573.6, 1
qelec at 298.15K 2 5.71615 7.82505 4 6.73212 4.28470 4 5.50495 4.02850 4

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 accessible states).


For a discussion of the symmetry numbers in NH3 see K. S. Pitzer, "The Symmetry Number and Thermodynamic Functions for Molecules Having Double Minimum Vibrations," J. Chem. Phys.,1939,7, 251-5.

Colby College, T. W. Shattuck, 5/20/06