The symmetry number of a molecule is obtained by imagining all identical atoms to
be labelled, and then counting the number of different but equivalent arrangements
that can be obtained by rotating (but not reflecting) the molecule. In the statistical-mechanical
treatment of chemical equilibrium
, the partition function
for each molecular species must be divided by its symmetry number.
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
on page 189
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook