A variationally computed room temperature line list for AsH₃

Abstract

Calculations are reported on the rotation-vibration energy levels of the arsine molecule with associated transition intensities. A potential energy surface (PES) obtained from ab initio electronic structure calculations is refined to experimental data, and the resulting energy levels display subwavenumber accuracy for all reliably known J = 0 term values under 6500 cm −1 . After a small empirical adjustment of the band centres, our calculated (J = 1 − 6) rovibrational states reproduce 578 experimentally derived energies with a root-mean-square error of 0.122 cm −1 . Absolute line intensities are computed using the refined PES and a new dipole moment surface (DMS) for transitions between states with energies up to 10 500 cm −1 and rotational quantum number J = 30.The computed DMS reproduces experimental line intensities to within 10% uncertainty for the ν 1 and ν 3 bands. Furthermore, our calculated absorption cross-sections display good agreement with the main absorption features recorded in Pacific Northwest National Laboratory (PNNL) for the complete range of 600 − 6500 cm −1 .Considering the unsuitability of the current state of AsH 3 data for either exoplanet modelling, which necessitates completeness, or industrial monitoring, which necessitates accuracy, we decided to construct a comprehensive line list for arsine which could be used for the applications mentioned above. Our approach to constructing linelists, as exploited in the ExoMol project 26,27 , uses potential energy surfaces which have been refined using spectroscopic data but ab initio dipole moment surfaces, which have J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-15 | 1

The infrared spectrum of PF3and analysis of rotational energy clustering effect

“…A clustering phenomena was found to occur which has been analysed using semi-classical methods and comparisons made with previous investigations into pyramidal spherical top molecules. It would be of interest to make further comparisons with even more pyramidal molecules, NF 3 or AsH 3 [115] for example, in order to investigate the effects of molecular properties (such as mass, equilibrium bond angle, rotational constant, how rigid the molecule is) on the formation of rotational clustering states. An ideal molecule to study experimentally would be accessible at room-temperature.…”

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

“…PES refinement is a technique where one adjusts the underlying ab initio surface to reproduce measured data to a high degree of accuracy, often to within a fraction of a wavenumber (Huang et al, 2012;Polyansky et al, 2018;Mizus et al, 2018;Bubukina et al, 2011). The method of Yurchenko et al (2003) has been successfully applied to numerous H 2 O potentials (Polyansky et al, 2018;Mizus et al, 2018;Bubukina et al, 2011), as well as to TiO (McKemmish et al, 2019), AsH 3 (Coles et al, 2019), NH 3 (Coles et al, 2018), CH 3 Cl (Owens et al, 2018) and C 2 H 4 (Mant et al, 2018). In this procedure, one maintains the overall structure of the underlying ab initio surface while simultaneously optimizing the parameters of the fit.…”

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

“…Approximately 16 000 electronic structure calculations were previously performed for a dipole moment surface at the MR-CI (multi-reference configuration interaction) level of theory utilizing an aug-cc-pCV6Z basis set (Dunning, 1989;Woon and Dunning Jr., 1995;Peterson and Dunning, 2002) and the Douglass-Kroll-Hess Hamiltonian of order two (DKH2) (Conway et al, 2018). These calculations span water bond lengths in the range of 1.3-4.0 a 0 with angles between 30 and 178 • .…”

“…The spectrum predicted by POKAZATEL has been tested against observations in our own atmosphere and was found to under-absorb in the near-ultraviolet (Lampel et al, 2017). To address this, a recently developed dipole moment surface (DMS), CKAPTEN (Conway et al, 2018), has been created through extensive electronic structure calculations, and spectra computed with this DMS have been shown to provide improvements over the POKAZATEL line list for wavelengths down to 400 nm (Conway et al, 2020a).…”