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

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 µm, 5 µm and 3 µm 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 ab initio dipole moment surface (DMS) is computed. Sev-eral spectroscopically-determined potential energy surfaces (PESs) are constructed by fitting to empirical energy levels in the region below 7000 cm −1 starting from an ab initio PES. Nuclear motion calculations using these new surfaces allow the unambiguous determination of the intensities of 10 µm band transitions, and the computation of the intensities of 10 µm and 5 µm bands within their experimental error. A decrease in intensities within the 3 µm 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.

Synthesis of ab initio and effective Hamiltonian line lists for ozone

“…A very accurate semi-empirical PES was obtained with a standard deviation of the fitted energy levels of only 0.027 cm −1 [20].…”

“…Here we will briefly discuss the two surfaces used for our ozone ab initio line list calculation. The ozone PES we have obtained in the [20] as follows. First an ab initio PES was calculated using the MOLPRO package [28] at the multi-reference configuration interaction (MRCI) level of theory and aug-cc-pwcVQZ basis set [20].…”

“…The ozone PES we have obtained in the [20] as follows. First an ab initio PES was calculated using the MOLPRO package [28] at the multi-reference configuration interaction (MRCI) level of theory and aug-cc-pwcVQZ basis set [20]. The accuracy of rovibrational energy levels calculation using this ab initio PES was a few cm −1 .…”

“…In this work we concentrate on the IR spectrum of ozone for which there are well-documented difficulties in determining transition intensities with the accuracy and consistency required for atmospheric studies [14,9,15]. This issue has led to a series of recent studies both experimental [16,17,18] and, in a new development for the field, ab initio [19,20,21].…”

“…In this paper we concentrate on the IR spectrum of 16 O 3 . Section 2 describes the calculation of the first principles ozone line list using our previously published semi-empirical potential energy surface (PES) [20] and ab initio the dipole moment surface (DMS), produced by Tyuterev and co-authors [21]. Program DVR3D [24] is used to solve nuclear-motion Schrödinger equation to produce ro-vibrational wavefunctions and to compute line positions and line intensities.…”