Physical versus non‐physical effective nuclear masses for non‐adiabatic corrections to molecular spectra

Two types of developments for very accurate non‐adiabatic corrections to rovibrational molecular energy levels, one of a formal nature and the other of a heuristic nature, lead to fundamentally different approaches for effective nuclear masses. The former yields effective masses that have non‐physic...

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Bibliographic Details
Published in:International journal of quantum chemistry 2024-01, Vol.124 (1), p.n/a
Main Authors: Pinto, J. Batista, Amaral, Paulo H. R., Diniz, Leonardo G., Mohallem, José R.
Format: Article
Language:English
Subjects:
effective nuclear mass
high resolution molecular spectroscopy
non‐adiabatic corrections
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Summary:Two types of developments for very accurate non‐adiabatic corrections to rovibrational molecular energy levels, one of a formal nature and the other of a heuristic nature, lead to fundamentally different approaches for effective nuclear masses. The former yields effective masses that have non‐physical interpretation at some ranges of nuclear distances. The later uses physical masses obtained from electronic structure calculations. This paper contains a brief review of the subject and proposes procedures to improve and generalize the heuristic approach. Comparisons are made of the results obtained by the two approaches for the H2 molecule, since no further calculations were found with the proper accuracy, but some issues involving the HeH+ ion and the water molecule are discussed. The conclusion is that the heuristic approach has many advantages over the formal one, namely, equivalent accuracy and physically grounded qualitative interpretation. But, moreover, it seems to be presently the only method that allows non‐adiabatic calculations for well isolated states of larger molecules. Nuclear effective masses used in the nuclear equation can account for non‐adiabatic effects in molecules, which are essencial to reach 10−1 – 10−2 cm−1 in the energy levels. Ab initio formal approaches produce non‐physycal masses, as the camel‐back form in the figure, besides being restricted to very small molecules. Heuristic methods add real electron masses to the nuclei, show expected physical behavior and are extensible to large molecules.
ISSN:0020-7608
1097-461X
DOI:10.1002/qua.27256