A semi-empirical potential energy surface and line list for H<sub>2</sub><sup>16</sup>O extending into the near-ultraviolet

Abstract

Abstract. Accurate reference spectroscopic information for the water molecule from the microwave to the near-ultraviolet is of paramount importance in atmospheric research. A semi-empirical potential energy surface for the ground electronic state of H216O has been created by refining almost 4000 experimentally determined energy levels. These states extend into regions with large values of rotational and vibrational excitation. For all states considered in our refinement procedure, which extend to 37 000 cm−1 and J=20 (total angular momentum), the average root-mean-square deviation is approximately 0.05 cm−1. This potential energy surface offers significant improvements when compared to recent models by accurately predicting states possessing high values of J. This feature will offer significant improvements in calculated line positions for high-temperature spectra where transitions between high J states become more prominent. Combining this potential with the latest dipole moment surface for water vapour, a line list has been calculated which extends reliably to 37 000 cm−1. Obtaining reliable results in the ultraviolet is of special importance as it is a challenging spectral region for the water molecule both experimentally and theoretically. Comparisons are made against several experimental sources of cross sections in the near-ultraviolet and discrepancies are observed. In the near-ultraviolet our calculations are in agreement with recent atmospheric retrievals and the upper limit obtained using broadband spectroscopy by Wilson et al. (2016, p. 194), but they do not support recent suggestions of very strong absorption in this region.

The 2024 Release of the Exomol Database: Molecular Line Lists for Exoplanetand Other Hot Atmospheres

“…Through a significant number of comparisons against high quality experimental and theoretical sources of spectroscopic data [221,222] , their results suggest there may be advantages of using their line lists in particular regions, primarily at short wavelengths. For this reason, a new room temperature H 16 2 O line list called WAT_UV296 [185] has been computed. This line list is available on the website and should be used for room temperature studies of spectra with λ < 0.5 μm.…”

Modeling of the atmospheric transmission of UV radiation with use of different data on water vapor absorption lines

“…The atmospheric transmission is calculated with H 2 O line parameters from POKAZATEL, data of Conway et al 6 , HITRAN2020 and W2020 databases, and intercomparison of the transmission spectra is made. The transmission at slant path through the atmosphere from 0 to 120 km was simulated with taking into account main absorbing gases in the UV region with various spectral resolutions.…”

“…In our work [4], the H 2 O lines contribution to absorption of solar radiation in the UV region was estimated for that H 2 O broadening line parameters were defined with use of JJ'-dependence 5 , and additional labeling of H 2 O lines from POKAZATEL line list was carried out. After POKAZATEL, the calculation of Conway et al 6 have appeared, where improved data on water potential energy surface and dipole moment surface were presented. The data of Conway are less complete in comparison with POKAZATEL line list because the transitions with angular momentum more than J=20 are absent there.…”

“…Also, the limitation on line intensity value is in data 6 but it is not important for the Earth's atmosphere applications. The calculation 6 is not limited by range and extended up to dissociation threshold. The H 2 O spectra at room temperature (296 K) with intensities 10 -30 cut off from POKAZATEL and data of Conway et al are shown in Fig.…”

EXOPLINES: Molecular Absorption Cross-Section Database for Brown Dwarf and Giant Exoplanet Atmospheres

“…More recently, Conway et al (2020) have published their H 2 O line list calculated from experimental spectroscopic data, which includes ∼10 6 transitions and it is limited up to J max =20. Their line lists have shown a significant improvement in the line position for the ultraviolet spectral region.…”