High accuracy water potential energy surface for the calculation of infrared spectra

TL;DR

This paper develops an ultra-precise water potential energy surface that enhances the accuracy of infrared spectral calculations, leading to a highly reliable line list for water vapor.

Contribution

It introduces an empirically refined high-accuracy potential energy surface for water, improving the precision of vibrational transition predictions.

Findings

Reproduces energy levels with a standard deviation of 0.011 cm⁻¹

Improves predicted transition intensities for problematic lines

Provides the most accurate water line list to date

Abstract

Transition intensities for small molecules such as water and CO$_2$ can now be computed with such high accuracy that they are being used to systematically replace measurements in standard databases. These calculations use high accuracy ab initio dipole moment surfaces and wavefunctions from spectroscopically-determined potential energy surfaces. Here an extra high accuracy potential energy surface (PES) of the water molecule (\hato) is produced starting from an ab initio PES which is then refined to empirical rovibrational energy levels. Variational nuclear motion calculations using this PES reproduce the fitted energy levels with a standard deviation of 0.011 \cm, approximately three times their stated uncertainty. Use of wavefunctions computed with this refined PES is found to improve the predicted transition intensities for selected (problematic) transitions. A new room temperature line list for H2(16)O is presented. It is suggested that the associated set of line intensities is the most accurate available to date for this species.