533 research outputs found
ExoMol at 10
No full textFor ten years, the ExoMol database of molecular line lists has provided vital spectroscopic data for the study of hot atmospheres. Jonathan Tennyson and Sergei N Yurchenko reflect on what the prject has achieved
High accuracy potential energy surface, dipole moment surface, rovibrational energies and line list calculations for 14NH3
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Previous issue date: 6We present a new spectroscopic potential energy surface (PES) for NH, produced by refining a high accuracy textit{ab initio} PESfootnote{Oleg L. Polyansky, Roman I. Ovsyannikov, Aleksandra A. Kyuberis, Lorenzo Lodi, Jonathan Tennyson, Andrey Yachmenev, Sergei N. Yurchenko, Nikolai F. Zobov, textit{J. Mol. Spec.}, 327 (2016) 21-30} to experimental energy levels taken predominantly from MARVELfootnote{Afaf R. Al Derzia, Tibor Furtenbacher, Jonathan Tennyson, Sergei N. Yurchenko, Attila G. Császár, textit{J. Quant. Spectrosc. Rad. Trans.}, 161 (2015) 117-130}. The PES reproduces 1722 matched J=0-8 experimental energies with a root-mean-square error of 0.035 cm-1 under 6000 cm and 0.059 under 7200 cm. In conjunction with a new DMS calculated using multi reference configuration interaction (MRCI) and H=aug-cc-pVQZ, N=aug-cc-pWCVQZ basis sets, an infrared (IR) line list has been computed which is suitable for use up to 2000 K. The line list is used to assign experimental lines in the 7500 - 10,500 cm region and previously unassigned lines in HITRAN in the 6000-7000 cm region
MOLECULAR LINE LISTS FOR SCANDIUM AND TITANIUM HYDRIDE USING THE DUO PROGRAM
No full textTransition-metal-containing (TMC) molecules often have very complex electronic spectra because of their large number of low-lying, interacting electronic states, of the large multi-reference character of the electronic states and of the large magnitude of spin-orbit and relativistic effects. As a result, fully ab initio calculations of line positions and intensities of TMC molecules have an accuracy which is considerably worse than the one usually achievable for molecules made up by main-group atoms only. In this presentation we report on new theoretical line lists for scandium hydride ScH and titanium hydride TiHfootnote{L. Lodi, S. N. Yurchenko and J. Tennyson, Mol. Phys. (Handy special issue) in press.}. Scandium and titanium are the lightest transition metal atoms and by virtue of their small number of valence electrons are amenable to high-level electronic-structure treatments and serve as ideal benchmark systems. We report for both systems energy curves, dipole curves and various coupling curves (including spin-orbit) characterising their electronic spectra up to about 20 000 cm-1. Curves were obtained using Internally-Contracted Multi Reference Configuration Interaction (IC-MRCI) as implemented in the quantum chemistry package MOLPRO. The curves where used for the solution of the coupled-surface ro-vibronic problem using the in-house program DUO footnote{S. N. Yurchenko, L. Lodi, J. Tennyson and A. V. Stolyarov, Computer Phys. Comms., to be submitted.}. DUO is a newly-developed, general program for the spectroscopy of diatomic molecules and its main functionality will be described.
The resulting line lists for ScH and TiH are made available as part of the Exomol project footnote{J. Tennyson and S. N. Yurchenko, Mon. Not. R. Astr. Soc. 2012, 425, 21. See also www.exomol.com.}.Made available in DSpace on 2016-01-05T20:01:47Z (GMT). No. of bitstreams: 3
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Previous issue date: 2
Non-resonant Raman spectra of the methyl radical 12CH3 simulated in variational calculations
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Previous issue date: 2019-06-21We report first-principles variational simulation of the non-resonant Raman spectrum for methyl radical (CH) in the electronic ground state. Calculations are based on a high level \emph{ab initio} potential energy and polarizability tensor surfaces of CH and employ accurate variational treatment of the ro-vibrational dynamics implemented in the general code TROVE [S. N. Yurchenko, W. Thiel, and P. Jensen, {\it J. Mol. Spectrosc.} {\bf 245}, 126--140 (2007); A. Yachmenev and S. N. Yurchenko, {\it J. Chem. Phys.} {\bf 143}, 014105 (2015)]. We extend the capabilities of TROVE towards simulations of the Raman spectra, which can in be applied to arbitrary molecule of moderate size. The simulations for CH are found to be in a good agreement with the available experimental data
Exomolhd: Recent Progresses On Photodissociation Of Small Molecules
No full textThe destruction of hot molecules by photodissociation influences the composition and dynamics of exoplanets, particularly in the presence of a UV-rich stellar environments. We compute temperature-dependent photodissociation cross sections and rates for molecules found in these atmospheres, for building a more realistic model of the planetary chemistry. The cross sections are calculated by solving the nuclear-motion Schrödinger equation as part of the ExoMol project using codes Duo, DVR3D and Exocross\footnote{Yurchenko \textit{et al} Comput Phys Commun 2016 \textbf{202} 262–275; Tennyson \textit{et al} Comput Phys Commun 2004 \textbf{163} 85-116; Yurchenko \textit{et al} A\&A 2018 \textbf{614} A131 }, using the methodology previously described\footnote{Pezzella \textit{et al} Phys. Chem. Chem. Phys. 2021 \textbf{23} 16390–16400}. Photodissociation rates are computed integrating the cross section with different stellar field models representing different star types. \\
New tools and results for HF, HCl and HCN. Cross sections and rates for the diatomics are compared with previously available data\footnote{Heays \textit{et al} A\&A 2017 \textbf{602} A105}, finding a good agreement for the interstellar medium for low temperatures. Both cross sections and rates have a dramatic temperature dependence for temperatures above 1000 K. Our results for HCN are compared with the results obtained by previous works employing the time dependent Schrödinger equation\footnote{Chenel \textit{et al} J. Chem. Phys. 2016 \textbf{144} 144306; Aguado \textit{et al} Astrophys. J. 2017 \textbf{838} 33 }
COMPUTING SPECTRA OF OPEN-SHELL DIATOMIC MOLECULES WITH DUO
No full text\textsc{Duo} is a program designed to solve a coupled Schr{\"o}dinger
equation for the motion of nuclei of a given diatomic molecule
characterized by an arbitrary set of electronic states.\footnote{ S.N. Yurchenko, L. Lodi, J. Tennyson, and A.V. Stolyarov, \textit{Comput. Phys. Commun.} \textbf{202}, 262 (2016).}
\textsc{Duo} is capable of both refining potential energy curves (by
fitting data to experimental energies or transition frequencies) and producing line lists.
Our most recent results of applying \textsc{Duo} to produce hot line lists for open-shell diatomic molecules include NO,\footnote{A. Wong, S. N. Yurchenko,
P. Bernath, H. S. P. Mueller, S. McConkey, and J. Tennyson, \textit{Mon. Not. R. Astron. Soc.} \textbf{470}, 882 (2017).} SiH,\footnote{S. N. Yurchenko, F. Sinden, L. Lodi, C. Hill, M. N. Gorman, and J. Tennyson, \textit{Mon. Not. R. Astron. Soc.} \textbf{473}, 5324 (2018)} PS and PO,\footnote{L. Prajapat, P. Jagoda, L. Lodi, M. N. Gorman, S. N. Yurchenko, and J. Tennyson, \textit{Mon. Not. R. Astron. Soc.} \textbf{472}, 3648 (2017).} C,\footnote{S. N. Yurchenko, J. Tennyson, and et al, \textit{Mon. Not. R. Astron. Soc.} in preparation (2018).} SN and SH,\footnote{S. N. Yurchenko, W. Bond, M. N. Gorman, L. Lodi, L. K. McKemmish, W. Nunn, R. Shah, and J. Tennyson, \textit{Mon. Not. R. Astron. Soc.} submitted (2018)} and AlH.\footnote{H. Williams, P. C. Leyland, L. Lodi, S. N. Yurchenko, and J. Tennyson, \textit{Mon. Not. R. Astron. Soc.} in preparation (2018).}
The published version of \textsc{Duo} only considers truly bound states.
We are now working on extending \textsc{Duo} to treat quasi-bound or resonance states, or indeed the continuum itself, using the stabilization method.\footnote{A.U. Hazi, H.S. Taylor, \textit{Phys. Rev. A} \textbf{1}, 1109 (1970)} As an illustration, we present simulations of spectra of the quasi-bound system A~ -- X~ of AlH and of the continuum system A~ -- X~ and B~ -- X~ of NaCl
The Electric Quadrupole Spectra Of Diatomic Molecules
No full textOwing to their molecular symmetry, many transitions of homonuclear diatomic molecules are forbidden in the electric dipole approximation. Instead their spectra are dominated by higher order transition moments, including the magnetic dipole moment and electric quadrupole moment.
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Here we present a new implementation of electric quadrupole transition moments in \textsc{Duo}\footnote{S.~N. Yurchenko, L.~Lodi, J.~Tennyson, A.~V. Stolyarov, \emph{Comput. Phys. Commun.}, 2016, \textbf{202}, 262 -- 275; publicly available at \textit{https://github.com/Trovemaster/Duo}.}. The implementation is validated against the highly accurate linelist of Roueff et al. \footnote{The full infrared spectrum of molecular hydrogen, Astron. Astrophys, 630 (2019)} for rovibrational transitions of the hydrogen molecule.
We also perform ab initio calculations for potential energy curves (PECs), electric quadrupole moment curves (EQCs), and spin-orbit coupling curves (SOCs) and demonstrate rovibronic linestrength calculations for the three lowest lying states (, and ) of molecular oxygen. Further demonstrations are provided for various other molecules of interest, including CO and HF as part of the ExoMol project \footnote{J.~Tennyson et al. \emph{J. Quant. Spectrosc. Radiat. Transf.}, 2020, \textbf{255}, 107228; \textit{www.exomol.com}.}. Absorption cross-sections are calculated using the \textsc{ExoCross} program\footnote{S.~N. {Yurchenko}, A.~F. {Al-Refaie}, J.~{Tennyson}, \emph{Astron. Astrophys};,
2018, \textbf{614}, A131; publicly available at \textit{https://github.com/Trovemaster/ExoCross}.}.Made available in DSpace on 2021-09-24T21:09:46Z (GMT). No. of bitstreams: 2
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Previous issue date: 2021-06-2
Exomol: molecular line list for exoplanets and other atmospheres
No full textThe discovery of extrasolar planets is one of the major scientific
advances of the last two decades. Thousands of planets have now been
detected and astronomers are beginning to characterize their
composition and physical characteristics. To do this requires a huge
quantity of spectroscopic data most of which are not available from
laboratory studies. The ExoMol project [1] is generating a
comprehensive solution to this problem by providing spectroscopic
data on all the molecular transitions of importance in the
atmospheres of exoplanets. These data are widely applicable to other
problems such studies on cool stars, brown dwarfs and circumstellar
environments as well as industrial and technological problems on earth.
ExoMol employs a mixture of first
principles and empirically tuned quantum mechanical methods
to compute comprehensive and very large rotation–vibration and
rovibronic line lists. Results span a variety of closed
(NaH, SiO, PN, NaCl, KCl, CS) and open (BeH, MgH, CaH, AlO, VO) shell
diatomics to triatomics (HCN/HNC, SO, HS, H),
tetratomics (HCO, PH, SO, HO), plus methane [2] and nitric acid [3]. This has led directly to the detection of new species
in the atmospheres of exoplanets [4]. A new comprehensive
data release has just been completed [5]. Progress on and future
prospects of the project will be summarised.
\bibliographystyle{default}
\begin{thebibliography}{5}
\bibitem{jt528} J. Tennyson, S.~N. Yurchenko, Mon. Not. R. astr. Soc., 425, 21, 2012.
\bibitem{jt572} S.~N. Yurchenko, J. Tennyson, J. Bailey, M.~D.~J. Hollis, G Tinetti, Proc. Nat. Acad. Sci., 111, 9379, 2014.
\bibitem{jt614} A.~I. Pavlyuchko, S.~N. Yurchenko, J. Tennyson, Mon. Not. R. astr. Soc., 452, 1702, 2015.
\bibitem{jt629} A. Tsiaras {\it et al}, Astrophys. J., in press.
[5] J. Tennyson {\it et al}, J. Mol. Spectrosc., in press.
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Previous issue date: 2016-06-2
AYTY: A NEW LINE-LIST FOR HOT FORMALDEHYDE
No full textbegin{abstract}
The ExoMol [1] project aims at providing spectroscopic data for key molecules that can be used to characterize the atmospheres of exoplanets and cool stars. Formaldehyde (HCO) is of growing importance in studying and modelling terrestrial atmospheric chemistry and dynamics. It also has relevance in astrophysical phenomena that include interstellar medium abundance, proto-planetary and cometary ice chemistry and masers from extra-galactic sources. However there gaps in currently available absolute intensities and a lack of higher rotational excitations that makes it unfeasible to accurately model high temperature systems such as hot Jupiters. Here we present textbf{AYTY} [2], a new line list for formaldehyde applicable to temperatures up to 1500 . AYTY contains almost 10 million states reaching rotational excitations up to and over 10 billion transitions at up to 10 000 cm. The line list was computed using the variational ro-vibrational solver TROVE with a refined textit{ab-initio} potential energy surface and dipole moment surface.
end{abstract}
begin{thebibliography}{1}
bibitem{jt528}
J.~Tennyson and S.~N. Yurchenko.
newblock {em MNRAS}, 425:21--33, 2012.
bibitem{jt597}
A.~F. Al-Refaie, S.~N. Yurchenko, A.~Yachmenev, and J.~Tennyson.
newblock {em MNRAS}, 2015.
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Previous issue date: 2
Non-adiabatic Calculations Of Spectra Of Open-shell Diatomic Molecules
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Non-adiabatic couplings (NACs) or derivative couplings (DDRs) between nearly degenerate states can be significant or even divergent. NACs arise from nuclear gradients of electronic wave functions around avoided crossings between adiabatic potential energy curves. Large values of NACs result in strong interaction between corresponding adiabatic states, making the adiabatic approximation invalid. In this work we consider NACs in the case of diatomic open-shell molecules and implement a diabatizaton methodology in the variatonal code \textsc{Duo}.\footnote{S.~N. Yurchenko, L.~Lodi, J.~Tennyson, A.~V. Stolyarov, \emph{Comput. Phys. Commun.}, 2016, \textbf{202}, 262 -- 275; publicly available at \textit{https://github.com/ExoMol}.} The methodology is based on a unitary transformation to the so-called quasi-diabatic states defined to provide smooth (with respect to nuclear coordinates) behaviour of different properties, such as spin-orbit curves, (transition) dipole moment curves etc. As example, rovibronic calculations of the electronic spectra of yttrium oxide, YO,\footnote{A.~N. Smirnov, V.~G. Solomonik, S.~N. Yurchenko, J.~Tennyson, \emph{Phys. Chem. Chem. Phys.}, 2019, \textbf{21}, 22794--22810.} in the quasi-diabatic representation will be presented.
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