Spectral lines in the
rotation-vibration spectrum of a gas that derive from the same change in rotation quantum number,
\(J\).
Notes: - \(\Delta J = J_{\rm{upper}} - J_{\rm{lower}} = -2, -1, 0, +1\ \rm{and}\ +2\) for the \(\rm{O}\), \(\rm{P}\), \(\rm{Q}\), \(\rm{R}\) and \(\rm{S}\) branches, respectively.
- The most commonly observed branches for simple molecules are the \(\rm{P}\), \(\rm{Q}\) and \(\rm{R}\) branches in infrared spectroscopy and the \(\rm{O}\), \(\rm{Q}\) and \(\rm{S}\) branches in Raman spectroscopy.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 762 (https://doi.org/10.1515/pac-2019-0203)