Influence of the linear term,
\(\Sigma_{k} (\partial \boldsymbol{\mu}/\partial Q_{k}) Q_{k}\), in the expansion of the electric dipole moment.
\(Q\) is the
normal coordinate.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 744 (https://doi.org/10.1515/pac-2019-0203)