Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)

Owens, Alec; Clark, Victoria; Mitrushchenkov, Alexander; Yurchenko, Sergei N.; Tennyson, Jonathan

doi:10.1063/5.0052958

“…A full-dimensional ab initio spectroscopic model of the Ã 2 Π-X 2 Σ + band system of CaOH has also been reported by the authors (Owens et al 2021a). High-level ab initio theory was used to construct new potential energy and transition dipole moment surfaces, and both Renner-Teller and spin-orbit coupling effects, which are essential for correctly reproducing the CaOH spectrum, were accounted for in the calculations.…”

Section: Introductionmentioning

confidence: 82%

“…Any correct description of the spectrum of CaOH must account for the Renner-Teller effect (Li & Coxon 1996, 1995Coxon et al 1994;Jarman & Bernath 1992;Coxon et al 1991;Hilborn et al 1983). In our spectroscopic model, the A and A surfaces are each represented by their own analytic function, essentially an eighth-order polynomial in terms of linear expansion variables of the bond lengths and bond angle, see Owens et al (2021a) for a detailed description. The A and A potential functions share the same parameter values for stretching only terms but possess different parameter values for terms involving the bending mode.…”

Section: Refinement Of the ã 2 π Potential Energy Surfacementioning

confidence: 99%

“…No studies of the O-H stretching ν3 mode have been carried out. As a result, we do not allow potential parameters related to the ν3 mode to vary in the refinement and they are instead fixed to the original ab initio values determined in Owens et al (2021a). Computed energy levels and transitions involving the ν3 mode will therefore not be as accurate as those involving only the ν1 and ν2 modes in the final line list.…”

Section: Refinement Of the ã 2 π Potential Energy Surfacementioning

confidence: 99%

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ExoMol line lists – XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)

Owens

¹

,

Mitrushchenkov

²

,

Yurchenko

³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Any future detection of the calcium monohydroxide radical (CaOH) in stellar and exoplanetary atmospheres will rely on accurate molecular opacity data. Here, we present the first comprehensive molecular line list of CaOH covering the $\tilde{A}\, ^2\Pi$–$\tilde{X}\, ^2\Sigma ^+$ rotation-vibration-electronic and $\tilde{X}\, ^2\Sigma ^+$–$\tilde{X}\, ^2\Sigma ^+$ rotation-vibration bands. The newly computed OYT6 line list contains over 24.2 billion transitions between 3.2 million energy levels with rotational excitation up to J = 175.5. It is applicable to temperatures up to T = 3000 K and covers the 0–35 000 cm−1 range (wavelengths λ > 0.29 μm) for rotational, rotation-vibration and the $\tilde{A}\, ^2\Pi$–$\tilde{X}\, ^2\Sigma ^+$ electronic transition. The strong band around 16 000 cm−1 (λ = 0.63 μm) is likely to be of interest in future astronomical observations, particularly in hot rocky exoplanets where temperatures can become extremely high. The OYT6 line list has been generated using empirically-refined $\tilde{X}\, ^2\Sigma ^+$ and $\tilde{A}\, ^2\Pi$ state potential energy surfaces, high-level ab initio transition dipole moment surfaces and a rigorous treatment of both Renner-Teller and spin-orbit coupling effects, which are necessary for correctly modelling the CaOH spectrum. Post-processing of the CaOH line list has been performed so as to tailor it to high-resolution applications, i.e. by replacing calculated energy levels with more accurate empirically-derived values (where available), hence improving the accuracy of the predicted line positions in certain regions. The OYT6 line list is available from the ExoMol database at http://www.exomol.com and the CDS astronomical database.

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“…8 Low-J transitions are generally more difficult to characterize with high accuracy at room temperature due to the lower population and, therefore, lower sensitivity. Hence, recent high-level ab initio calculations used J = 3/2 state data for the adjustment of parameters of potential energy surfaces (Owens et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Low-J Transitions in A˜2Π(0,0,0)−X˜2Σ+(0,0,0) Band of Buffer-gas-cooled CaOH

Takahashi

¹

,

Baba

²

,

Enomoto

³

et al. 2022

ApJ

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Calcium monohydroxide radical (CaOH) is receiving an increasing amount of attention from the astrophysics community as it is expected to be present in the atmospheres of hot rocky super-Earth exoplanets as well as interstellar and circumstellar environments. Here, we report the high-resolution laboratory absorption spectroscopy on low-J transitions in A ˜ 2 Π ( 0 , 0 , 0 ) − X ˜ 2 Σ + ( 0 , 0 , 0 ) band of buffer-gas-cooled CaOH. In total, 40 transitions out of the low-J states were assigned, including 27 transitions that have not been reported in previous literature. The determined rotational constants for both ground and excited states are in excellent agreement with previous literature, and the measurement uncertainty for the absolute transition frequencies was improved by more than a factor of 3. This will aid future interstellar, circumstellar, and atmospheric identifications of CaOH. The buffer-gas-cooling method employed here is a particularly powerful method to probe low-J transitions and is easily applicable to other astrophysical molecules.

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“…Low-J transitions are generally more difficult to characterize with high accuracy at room temperature due to the lower population and, therefore, lower sensitivity. Hence, recent high-level ab initio calculations used J = 3/2 states data for the adjustment of parameters of potential energy surfaces (Owens et al (2021)).…”

mentioning

confidence: 99%

Low-$J$ transitions in $\tilde{A}^2Π(0,0,0)-\tilde{X}^2Σ^+(0,0,0)$ band of buffer-gas-cooled CaOH

Takahashi¹,

Baba²,

Enomoto³

et al. 2022

Preprint

0

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Calcium monohydroxide radical (CaOH) is receiving an increasing amount of attention from the astrophysics community as it is expected to be present in the atmospheres of hot rocky super-Earth exoplanets as well as interstellar and circumstellar environments. Here, we report the high-resolution laboratory absorption spectroscopy on low-J transitions in Ã2 Π(0, 0, 0) − X2 Σ + (0, 0, 0) band of buffer-gas-cooled CaOH. In total, 40 transitions out of the low-J states were assigned, including 27 transitions which have not been reported in previous literature. The determined rotational constants for both ground and excited states are in excellent agreement with previous literature, and the measurement uncertainty for the absolute transition frequencies was improved by more than a factor of three. This will aid future interstellar, circumstellar, and atmospheric identifications of CaOH. The buffer-gas-cooling method employed here is a particularly powerful method to probe low-J transitions and is easily applicable to other astrophysical molecules. 1. INTRODUCTION Calcium monohydroxide molecules ( 40 Ca 16 O 1 H) now have a special standing because of their expected presence in the atmospheres of hot rocky super-Earth exoplanets (Bernath (2009); Rajpurohit, A. S. et al. (2013); Tennyson & Yurchenko ( 2017)). Determining accurate spectroscopic parameters and transition frequencies on relatively simple molecules present in this environment are necessary for exploration of hot rocky super-Earths. Because of highly abundant Ca atoms, CaOH could also be found in interstellar and circumstellar spaces, where the temperature is sometimes in the 10s of kelvin regime. In fact, CaOH has been detected in cool stellar atmospheres at low spectral resolution (Rajpurohit, A. S. et al. (2016)). CaOH is therefore an excellent spectroscopic target species.

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Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)

Cited by 9 publications

References 59 publications

ExoMol line lists – XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)

ExoMol line lists – XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)

Low-J Transitions in A˜2Π(0,0,0)−X˜2Σ+(0,0,0) Band of Buffer-gas-cooled CaOH

Low-$J$ transitions in $\tilde{A}^2Π(0,0,0)-\tilde{X}^2Σ^+(0,0,0)$ band of buffer-gas-cooled CaOH

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