Potential energy surface, dipole moment surface and the intensity calculations for the 10 micron, 5 micron, and 3 micron bands of ozone

TL;DR

This study uses advanced quantum chemical methods to accurately compute potential energy and dipole moment surfaces for ozone, improving the reliability of spectroscopic intensity data for key atmospheric monitoring bands.

Contribution

It introduces a new high-accuracy ab initio dipole moment surface and refined potential energy surfaces, enabling more precise ozone spectral intensity calculations.

Findings

Accurate intensities for 10 μm ozone bands were determined.

Predicted decrease in 3 μm band intensities aligns with atmospheric data.

Enhanced surfaces facilitate future comprehensive ozone line list computations.

Abstract

Monitoring ozone concentrations in the Earth's atmosphere using spectroscopic methods is a major activity which undertaken both from the ground and from space. However there are long-running issues of consistency between measurements made at infrared (IR) and ultraviolet (UV) wavelengths. In addition, key O$_3$ IR bands at 10 \muu, 5 \muu\ and 3 \muu\ also yield results which differ by a few percent when used for retrievals. These problems stem from the underlying laboratory measurements of the line intensities. Here we use quantum chemical techniques, first principles electronic structure and variational nuclear-motion calculations, to address this problem. A new high-accuracy \ai\ dipole moment surface (DMS) is computed. Several spectroscopically-determined potential energy surfaces (PESs) are constructed by fitting to empirical energy levels in the region below 7000 \cm\ starting from an \ai\ PES. Nuclear motion calculations using these new surfaces allow the unambiguous determination of the intensities of 10 \muu\ band transitions, and the computation of the intensities of 10 \muu\ and 5 \muu\ bands within their experimental error. A decrease in intensities within the 3 \muu\ is predicted which appears consistent with atmospheric retrievals. The PES and DMS form a suitable starting point both for the computation of comprehensive ozone line lists and for future calculations of electronic transition intensities