Nonadiabatic Calculation of Dipole Moments

TL;DR

This paper reviews nonadiabatic calculations of molecular dipole moments, emphasizing the importance of coordinate choice, and compares them with standard Born--Oppenheimer methods and experimental estimations.

Contribution

It highlights the limitations of laboratory-fixed coordinate calculations and discusses more accurate molecule-fixed frame approaches for dipole moment computation.

Findings

Laboratory-fixed coordinate calculations often fail for dipole moments.

Molecule-fixed frame calculations provide more reliable results.

Experimental Stark shift measurements do not directly yield dipole moments.

Abstract

We review some of the few available nonadiabatic calculations of dipole moments. We show that those carried out in a laboratory-fixed set of coordinate axes are bound to fail and discuss the more reasonable ones in a molecule-fixed reference frame. For completeness we also describe the standard Born--Oppenheimer calculations of dipole moments. We briefly address the experimental estimation of dipole moments from the Stark shift of spectral lines and argue that it does not provide such property but a sort of energy--weighted average of dipole transition moments.