741 research outputs found
The Status of Spectroscopic Data for the Exoplanet Characterisation Missions
The status of laboratory spectroscopic data for exoplanet characterisation
missions such as EChO is reviewed. For many molecules (eg H2O, CO, CO2, H3+,
O2, O3) the data are already available. For the other species work is actively
in progress constructing this data. Much of the is work is being undertaken by
ExoMol project (www.exomol.com). This information will be used to construct and
EChO-specific spectroscopic database.Comment: Experimental Astronomy, accepte
ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K
A new hot line list is calculated for CH in its ground electronic
state. This line list, called 10to10, contains 9.8 billion transitions and
should be complete for temperatures up to 1500 K. It covers the wavelengths
longer than 1 m and includes all transitions to upper states with energies
below cm and rotational excitation up to . The
line list is computed using the eigenvalues and eigenfunctions of CH
obtained by variational solution of the Schr\"{o}dinger equation for the
rotation-vibration motion of nuclei employing program TROVE. An ab initio
dipole moment surface and a new 'spectroscopic' potential energy surface are
used. Detailed comparisons with other available sources of methane transitions
including HITRAN, experimental compilations and other theoretical line lists
show that these sources lack transitions both higher temperatures and near
infrared wavelengths. This line list is suitable for modelling atmospheres of
cool stars and exoplanets. It is available from the CDS database as well as at
www.exomol.com.Comment: Submitted to MNRA
The ExoMol Atlas of Molecular Opacities
The ExoMol project is dedicated to providing molecular line lists for
exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab
initio calculations and available laboratory data. The actual line lists are
generated using variational nuclear motion calculations. These line lists form
the input for opacity models for cool stars and brown dwarfs as well as for
radiative transport models involving exoplanets. This paper is a collection of
molecular opacities for 52 molecules (130 isotopologues) at two reference
temperatures, 300 K and 2000 K, using line lists from the ExoMol database. So
far, ExoMol line lists have been generated for about 30 key molecular species.
Other line lists are taken from external sources or from our work predating the
ExoMol project. An overview of the line lists generated by ExoMol thus far is
presented and used to evaluate further molecular data needs. Other line lists
are also considered. The requirement for completeness within a line list is
emphasized and needs for further line lists discussed
Ab initio R-matrix calculations of e+-molecule scattering
The adaptation of the molecular R-matrix method, originally developed for electron-molecule collision studies, to positron scattering is discussed. Ab initio R-matrix calculations are presented for collisions of low energy positrons with a number of diatomic systems including H2, HF and N2. Differential elastic cross sections for positron-H2 show a minimum at about 45 deg for collision energies between 0.3 and 0.5 Ryd. The calculations predict a bound state of positronHF. Calculations on inelastic processes in N2 and O2 are also discussed
Laboratory spectra of hot molecules: data needs for hot super-Earth exoplanets
The majority of stars are now thought to support exoplanets. Many of those
exoplanets discovered thus far are categorized as rocky objects with an
atmosphere. Most of these objects are however hot due to their short orbital
period. Models suggest that water is the dominant species in their atmospheres.
The hot temperatures are expected to turn these atmospheres into a (high
pressure) steam bath containing remains of melted rock. The spectroscopy of
these hot rocky objects will be very different from that of cooler objects or
hot gas giants. Molecules suggested to be important for the spectroscopy of
these objects are reviewed together with the current status of the
corresponding spectroscopic data. Perspectives of building a comprehensive
database of linelist/cross sections applicable for atmospheric models of rocky
super-Earths as part of the ExoMol project are discussed. The
quantum-mechanical approaches used in linelist productions and their challenges
are summarized.Comment: Molecular Astrophysics (in press) Review article 96 pages, 17
Figures, 2 Tables, 267 reference
ExoMol: molecular line lists for exoplanet and other atmospheres
The discovery of extrasolar planets is one of the major scientific advances
of the last two decades. Hundreds of planets have now been detected and
astronomers are beginning to characterise their composition and physical
characteristics. To do this requires a huge quantity of spectroscopic data most
of which is not available from laboratory studies. The ExoMol project will
offer a comprehensive solution to this problem by providing spectroscopic data
on all the molecular transitions of importance in the atmospheres of
exoplanets. These data will be widely applicable to other problems and will be
used for studies on cool stars, brown dwarfs and circumstellar environments.
This paper lays out the scientific foundations of this project and reviews
previous work in this area.
A mixture of first principles and empirically-tuned quantum mechanical
methods will be used to compute comprehensive and very large rotation-vibration
and rotation-vibration-electronic (rovibronic) line lists. Methodologies will
be developed for treating larger molecules such as methane and nitric acid.
ExoMol will rely on these developments and the use of state-of-the-art
computing.Comment: MNRAS (in press
CN excitation and electron densities in diffuse molecular clouds
Utilising previous work by the authors on the spin-coupled rotational
cross-sections for electron-CN collisions, data for the associated rate
coefficients is presented. Data on rotational, fine-structure and
hyperfine-structure transition involving rotational levels up to =20 are
computed for temperatures in the range 10 -- 1000~K. Rates are calculated by
combining Born-corrected R-matrix calculations with the infinite-order-sudden
(IOS) approximation. The dominant hyperfine transitions are those with . For dipole-allowed transitions, electron-impact rates
are shown to exceed those for excitation of CN by para-H() by five
orders of magnitude. The role of electron collisions in the excitation of CN in
diffuse clouds, where local excitation competes with the cosmic microwave
background (CMB) photons, is considered. Radiative transfer calculations are
performed and the results compared to observations. These comparisons suggest
that electron density lies in the range ~cm for
typical physical conditions present in diffuse clouds.Comment: 6 pages, 8 figures, accepted 14/08/201
A parallel algorithm for Hamiltonian matrix construction in electron-molecule collision calculations: MPI-SCATCI
Construction and diagonalization of the Hamiltonian matrix is the
rate-limiting step in most low-energy electron -- molecule collision
calculations. Tennyson (J Phys B, 29 (1996) 1817) implemented a novel algorithm
for Hamiltonian construction which took advantage of the structure of the
wavefunction in such calculations. This algorithm is re-engineered to make use
of modern computer architectures and the use of appropriate diagonalizers is
considered. Test calculations demonstrate that significant speed-ups can be
gained using multiple CPUs. This opens the way to calculations which consider
higher collision energies, larger molecules and / or more target states. The
methodology, which is implemented as part of the UK molecular R-matrix codes
(UKRMol and UKRMol+) can also be used for studies of bound molecular Rydberg
states, photoionisation and positron-molecule collisions.Comment: Write up of a computer program MPI-SCATCI Computer Physics
Communications, in pres
Line Lists For High Resolution Studies Of Exoplanets
The ExoMol project (www.exomol.com) provides comprehensive line lists
for the study of exoplanets and other hot bodies. As part of the ERC-funded ExoMolHD project these line lists are being refactored to facilitate their use in characterization of exoplanets using high resolution Doppler shift spectroscopy. This technique is based the use of MARVEL (measured active rotation vibration energy level) to obtain empirical energy levels and illustrated by a recent study on formaldhyde (HCO).\footnote{A. R. {Al-Derzi}, S. N. Yurchenko, J. Tennyson, M. Melosso, Ningjing Jiang, C. Puzzarini, L. Dore, T. Furtenbacher, R. Tobias and A G. Cs\'asz\'ar, 2021, J. Quant. Spectrosc. Radiat. Transf.,
doi = {10.1016/j.jqsrt.2021.107563}}
For formaldehyde we analysed of 16\,596 non-redundant transitions from 43 experimental sources and resulted in the determination of 5029 empirical energy levels. As part of this work new measurements were performed in Bologna yielding high-accuracy rotational transitions
within the ground, \nub{3}, \nub{4} and \nub{6} vibrational states,
significantly improving the overall accuracy of the network. Eleven
artificial transitions determined from effective Hamiltonian fits were added to the network to both fix the gap between ortho and para levels, and to join free-standing networks of transitions to the main network.
\begin{wrapfigure}{r}{0pt}
\includegraphics[trim=0 0 0 3cm,scale=0.2]{H2CO_MARVEL_1000-2000.eps}
\end{wrapfigure}
The empirical energies were used to update the AYTY ExoMol line list for formaldehyde. This yielded 367\,779 transition frequencies determined
using the empirical energy levels of which
183\,673 lie above the dynamic HITRAN intensity cutoff, see the example in the figure.
The generation of line lists which combine empirically-determined transition wavenumbers with {\it ab initio} transition dipoles is suitable for high resolution
studies of both the Earth's and exoplanetary atmospheres.
High resoltion line lists for other molecules starting with AlO, VO and the isotopologues of H are currently being prepared
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