ExoMol line lists – XVIII. The high-temperature spectrum of VO

McKemmish, Laura K.; Yurchenko, Sergei N.; Tennyson, Jonathan

doi:10.1093/mnras/stw1969

Cited by 176 publications

(64 citation statements)

References 110 publications

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“…These will be used to fit a full spectroscopic model for VO and, from this model, a full spectroscopic line list for this system. Work on this is well advanced and the results will be reported elsewhere [80].…”

Section: Resultsmentioning

confidence: 90%

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Ab initiocalculations to support accurate modelling of the rovibronic spectroscopy calculations of vanadium monoxide (VO)

2016

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Accurate knowledge of the rovibronic near-infrared and visible absorption spectra of transition metal diatomic species like vanadium monoxide (VO) is very important for studies of cool stellar and hot planetary atmospheres. Here, the required ab initio curves are produced for the dipole moment and spin-orbit coupling, both diagonal and off-diagonal. The reliability of these curves is estimated by comparing potential energy surfaces obtained using the same methodology against experimental data (e.g. excitation energies, vibrational frequencies, bond distances). The ab initio data produced here forms the basis of a new spectroscopic model for the rovibronic spectroscopy of VO. This model has been used to produce a new VO line list which considers 13 different electronic states and contains almost 640,000 energy levels and over 277 million transitions.Open shell transition metal diatomics are challenging species to model through ab initio quantum mechanics due to the large number of low-lying electronic states, significant relativistic effects (particularly strong spin-orbit coupling within and between electronic states) and strong static and dynamic electron correlation. Multi-reference configuration interaction (MRCI) methodologies using orbitals from a complete active space self-consistent-field (CASSCF) calculation are the standard technique for this kinds of system. We use different state-specific or minimal-state CASSCF orbitals for each electronic state to maximise the accuracy of the calculation. We demonstrate that this choice of orbitals significantly affects the quality of the property calculations by comparing results using CASSCF orbitals optimised for different numbers of states.The off-diagonal dipole moment, or the transition moment, is the critical property controlling the intensity of electronic transitions. We test the use of finite-field off-diagonal dipole moments, but found that (1) the accuracy of the excitation energies were not sufficient to allow accurate dipole moments to be evaluated and (2) computer time requirements for perpendicular transitions were prohibitive. The best off-diagonal dipole moments are calculated using wavefunctions with different CASSCF orbitals.

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Section: Resultsmentioning

confidence: 90%

“…Details on the way in which these diagonal dipole moments are used in the final line list are given in Ref. [80]. In brief, for our final line list, we choose to use ab initio points only where the calculations were trusted and the curves smooth.…”

Section: Diagonal Dipole Momentsmentioning

confidence: 99%

Ab initiocalculations to support accurate modelling of the rovibronic spectroscopy calculations of vanadium monoxide (VO)

2016

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“…To calculate the cross-section of VO, the ExoMol line list (McKemmish et al 2016, Tennyson & Yurchenko 2012) was used. The TiO cross-sections were generated using three different line lists: Plez (1998) (Grimm & Heng 2015) assuming a Voigt line profile with thermal and natural broadening only at a resolution of 0.01 cm −1 with an absolute line wing cut-off of 100 cm −1 .…”

Section: Parametermentioning

confidence: 99%

Non-detection of TiO and VO in the atmosphere of WASP-121b using high-resolution spectroscopy

Merritt

Gibson

Nugroho

et al. 2020

A&A

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Thermal inversions have long been predicted to exist in the atmospheres of ultra-hot Jupiters. However, detection of two species thought to be responsible -TiO and VO -remain elusive. We present a search for TiO and VO in the atmosphere of the ultra-hot Jupiter WASP-121b (T eq 2400 K), an exoplanet already known to show water features in its dayside spectrum characteristic of a temperature inversion as well as tentative evidence for VO at low-resolution. We observed its transmission spectrum with UVES/VLT and used the cross-correlation method -a powerful tool for the unambiguous identification of the presence of atomic and molecular species -in an effort to detect whether TiO or VO were responsible for the observed temperature inversion. No evidence for the presence of TiO or VO was found at the terminator of WASP-121b. By injecting signals into our data at varying abundance levels, we set rough detection limits of [VO] −7.9 and [TiO] −9.3. However, these detection limits are largely degenerate with scattering properties and the position of the cloud deck. Our results may suggest that neither TiO or VO are the main drivers of the thermal inversion in WASP-121b, but until a more accurate line list is developed for VO, we cannot conclusively rule out its presence. Future work will search for finding other strong optically-absorbing species that may be responsible for the excess absorption in the redoptical.

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“…This is especially important when working with line lists containing tens of billions lines. At different stages of development ExoCross was used to generate spectra by Underwood et al (2016b,a); McKemmish et al (2016); Wong et al (2017); ; Yurchenko et al (2017a); Owens et al (2017); Prajapat et al (2017); Yurchenko et al (2018) and Rutkowski et al (2018).…”

Section: Introductionmentioning

confidence: 99%

EXOCROSS: a general program for generating spectra from molecular line lists

Yurchenko

Al-Refaie

Tennyson

2018

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166

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ExoCross is a Fortran code for generating spectra (emission, absorption) and thermodynamic properties (partition function, specific heat etc.) from molecular line lists. Input is taken in several formats, including ExoMol and HITRAN formats. ExoCross is efficiently parallelized showing also a high degree of vectorization. It can work with several line profiles such as Doppler, Lorentzian and Voigt and support several broadening schemes. Voigt profiles are handled by several methods allowing fast and accurate simulations. Two of these methods are new. ExoCross is also capable of working with the recently proposed method of super-lines. It supports calculations of lifetimes, cooling functions, specific heats and other properties. ExoCross can be used to convert between different formats, such as HITRAN, ExoMol and Phoenix. It is capable of simulating non-LTE spectra using a simple two-temperature approach. Different electronic, vibronic or vibrational bands can be simulated separately using an efficient filtering scheme based on the quantum numbers.

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ExoMol line lists – XVIII. The high-temperature spectrum of VO

Cited by 176 publications

References 110 publications

Ab initiocalculations to support accurate modelling of the rovibronic spectroscopy calculations of vanadium monoxide (VO)

Ab initiocalculations to support accurate modelling of the rovibronic spectroscopy calculations of vanadium monoxide (VO)

Non-detection of TiO and VO in the atmosphere of WASP-121b using high-resolution spectroscopy

EXOCROSS: a general program for generating spectra from molecular line lists

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