Perspective: Accurate ro-vibrational calculations on small molecules

TL;DR

This paper reviews the current state of high-accuracy variational ro-vibrational calculations for small molecules, highlighting their increasing role in spectroscopy, atmospheric modeling, and future research directions.

Contribution

It discusses advancements in ab initio variational calculations, including the consideration of small effects like QED, and their impact on spectroscopy and molecular studies.

Findings

Calculations are now competitive with experimental data.

Variational methods generate extensive transition data for atmospheric models.

Future work includes studying near-dissociation states and chemical reactions.

Abstract

In what has been described as the fourth age of Quantum Chemistry, variational nuclear motion programs are now routinely being used to obtain the vibration-rotation levels and corresponding wavefunctions of small molecules to the sort of high accuracy demanded by comparison with spectroscopy. In this perspective I will discuss the current state-of-the-art which, for example, shows that these calculations are increasingly competitive with measurements or, indeed, replacing them and thus becoming the primary source of data on key processes. To achieve this accuracy {\it ab initio} requires consideration small effects, routinely ignored in standard calculations, such those due to quantum electrodynamics (QED). Variational calculations are being used to generate huge list of transitions which provide the input for models of radiative transport through hot atmospheres and to fill in or even replace measured transition intensities. Future prospects such as study of molecular states near dissociation, which can provide a link with low-energy chemical reactions, are discussed.