arXiv subjects

Sergei N. Yurchenko

Publications and source records attributed to Sergei N. Yurchenko.

At least 127 records · Page 7Linked to original sources

arXiv2016

Duo: a general program for calculating spectra of diatomic molecules

Duo is a general, user-friendly program for computing rotational, rovibrational and rovibronic spectra of diatomic molecules. Duo solves the Schrödinger equation for the motion of the nuclei not only for the simple case of uncoupled, isolated electronic states (typical for the ground state of closed-shell diatomics) but also for the general case of an arbitrary number and type of couplings between electronic states (typical for open-shell diatomics and excited states). Possible couplings include spin-orbit, angular momenta, spin-rotational and spin-spin. Corrections due to non-adiabatic effects can be accounted for by introducing the relevant couplings using so-called Born-Oppenheimer breakdown curves. Duo requires user-specified potential energy curves and, if relevant, dipole moment, coupling and correction curves. From these it computes energy levels, line positions and line intensities. Several analytic forms plus interpolation and extrapolation options are available for representation of the curves. Duo can refine potential energy and coupling curves to best reproduce reference data such as experimental energy levels or line positions. Duo is provided as a Fortran 2003 program and has been tested under a variety of operating systems.

physics.comp-ph↗

arXiv2016

ExoMol molecular line lists - XVI: The rotation-vibration spectrum of hot H$_2$S

This work presents the AYT2 line list: a comprehensive list of 114 million $^{1}$H$_2$$^{32}$S vibration-rotation transitions computed using an empirically-adjusted potential energy surface and an {\it ab initio} dipole moment surface. The line list gives complete coverage up to 11000 \cm\ (wavelengths longer than 0.91 $μ$m) for temperatures up to 2000 K. Room temperature spectra can be simulated up to 20000 \cm\ (0.5 $μ$m) but the predictions at visible wavelengths are less reliable. AYT2 is made available in electronic form as supplementary data to this article and at \url{www.exomol.com}.

astro-ph.EP↗

arXiv2016

ExoMol line lists XV: A new hot line list for hydrogen peroxide

A computed line list for hydrogen peroxide, H$_2{}^{16}$O$_2$, applicable to temperatures up to $T=1250$~K is presented. A semi-empirical high accuracy potential energy surface is constructed and used with an {\it ab initio} dipole moment surface as input TROVE to compute 7.5 million rotational-vibrational states and around 20 billion transitions with associated Einstein-$A$ coefficients for rotational excitations up to $J=85$. The resulting APTY line list is complete for wavenumbers below 6~000 cm$^{-1}$ ($λ< 1.67$~$μ$m) and temperatures up to 1250~K. Room-temperature spectra are compared with laboratory measurements and data currently available in the HITRAN database and literature. Our rms with line positions from the literature is 0.152 \cm\ and our absolute intensities agree better than 10\%. The full line list is available from the CDS databas

astro-ph.EP↗

arXiv2016

Experimental energy levels and partition function of the $^{12}$C$_2$ molecule

The carbon dimer, the $^{12}$C$_2$ molecule, is ubiquitous in astronomical environments. Experimental-quality rovibronic energy levels are reported for $^{12}$C$_2$, based on rovibronic transitions measured for and among its singlet, triplet, and quintet electronic states, reported in 42 publications. The determination utilizes the Measured Active Rotational-Vibrational Energy Levels (MARVEL) technique. The 23,343 transitions measured experimentally and validated within this study determine 5,699 rovibronic energy levels, 1,325, 4,309, and 65 levels for the singlet, triplet, and quintet states investigated, respectively. The MARVEL analysis provides rovibronic energies for six singlet, six triplet, and two quintet electronic states. For example, the lowest measurable energy level of the \astate\ state, corresponding to the $J=2$ total angular momentum quantum number and the $F_1$ spin-multiplet component, is 603.817(5) \cm. This well-determined energy difference should facilitate observations of singlet--triplet intercombination lines which are thought to occur in the interstellar medium and comets. The large number of highly accurate and clearly labeled transitions that can be derived by combining MARVEL energy levels with computed temperature-dependent intensities should help a number of astrophysical observations as well as corresponding laboratory measurements. The experimental rovibronic energy levels, augmented, where needed, with {\it ab initio} variational ones based on empirically adjusted and spin-orbit coupled potential energy curves obtained using the \Duo\ code, are used to obtain a highly accurate partition function, and related thermodynamic data, for $^{12}$C$_2$ up to 4,000 K.

astro-ph.GA↗

arXiv2016

ExoMol molecular line lists - XIV: The rotation-vibration spectrum of hot SO$_2$

Sulphur dioxide is well-known in the atmospheres of planets and satellites, where its presence is often associated with volcanism, and in circumstellar envelopes of young and evolved stars as well as the interstellar medium. This work presents a line list of 1.3 billion $^{32}$S$^{16}$O$_2$ vibration-rotation transitions computed using an empirically-adjusted potential energy surface and an ab initio dipole moment surface. The list gives complete coverage up to 8000 cm$^{-1}$ (wavelengths longer than 1.25 $μ$m) for temperatures below 2000 K. Infrared absorption cross sections are recorded at 300 and 500 C are used to validated the resulting ExoAmes line list. The line list is made available in electronic form as supplementary data to this article and at www.exomol.com.

astro-ph.EP↗

arXiv2016

Detecting chirality in molecules by linearly polarized laser fields

A new scheme for enantiomer differentiation of chiral molecules using a pair of linearly polarized intense ultrashort laser pulses with skewed mutual polarization is presented. The technique relies on the fact that the off-diagonal anisotropic contributions to the electric polarizability tensor for two enantiomers have different signs. Exploiting this property, we are able to excite a coherent unidirectional rotation of two enantiomers with a π phase difference in the molecular electric dipole moment. The approach is robust and suitable for relatively high temperatures of molecular samples, making it applicable for selective chiral analysis of mixtures, and to chiral molecules with low barriers between enantiomers. As an illustration, we present nanosecond laser-driven dynamics of a tetratomic non-rigid chiral molecule with short-lived chirality. The ultrafast time scale of the proposed technique is well suited to study parity violation in molecular systems in short-lived chiral states.

physics.chem-ph↗

arXiv2016

Radiative lifetimes and cooling functions for astrophysically important molecules

Extensive line lists generated as part of the ExoMol project are used to compute lifetimes for individual rotational, rovibrational and rovibronic excited states, and temperature-dependent cooling functions by summing over all dipole-allowed transitions for the states concerned. Results are presented for SiO, CaH, AlO, ScH, H$_2$O and methane. The results for CH$_4$ are particularly unusual with 4 excited states with no dipole-allowed decay route and several others where these decays lead to exceptionally long lifetimes. These lifetime data should be useful in models of masers and estimates of critical densities, and can provide a link with laboratory measurements. Cooling functions are important in stellar and planet formation.

physics.chem-ph↗

arXiv2015

ExoMol molecular line lists - XIII: The spectrum of CaO

An accurate line list for calcium oxide is presented covering transitions between all bound ro-vibronic levels from the five lowest electronic states \X, \Ap, \A, \astate, and \bstate. The ro-vibronic energies and corresponding wavefunctionts were obtained by solving the fully coupled Schrödinger equation. \textit{Ab initio} potential energy, spin-orbit, and electronic angular momentum curves were refined by fitting to the experimental frequencies and experimentally derived energies available in the literature. Using our refined model we could (i) reassign the vibronic states for a large portion of the experimentally derived energies [van Groenendael A., Tudorie M., Focsa C., Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255], (ii) extended this list of energies to $J=79-118$ and (iii) suggest a new description of the resonances from the \A--\X\ system. We used high level \textit{ab initio} electric dipole moments reported previously [Khalil H., Brites V., Le Quere F., Leonard C., 2011, Chem. Phys., 386, 50] to compute the Einstein A coefficients. Our work is the first fully coupled description of this system. Our line list is the most complete catalogue of spectroscopic transitions available for $^{40}$Ca$^{16}$O and is applicable for temperatures up to at least 5000~K. CaO has yet to be observed astronomically but its transitions are characterised by being particularly strong which should facilitate its detection. The CaO line list is made available in an electronic form as supplementary data to this article and at \url{www.exomol.com}.

astro-ph.GA↗

arXiv2015

ExoMol molecular line lists: XI The spectrum of nitric acid

Nitric acid is a possible biomarker in the atmospheres of exoplanets. An accurate line list of rotational and rotational-vibrational transitions is computed for nitric acid (HNO$_3$). This line list covers wavelengths longer than 1.42 $μ$m (0 - 7000 cm$^{-1}$) and temperatures up to 500 K. The line list is computed using a hybrid variational -- perturbation theory and empirically tuned potential energy and dipole surfaces. It comprises almost 7 billion transitions involving rotations up to $J=100$. Comparisons with spectra from the HITRAN and PNNL databases demonstrate the accuracy of our calculations. Synthetic spectra of water - nitric acid mixturessuggest that nitric acid has features at 7.5 and 11.25 $μ$m that are capable of providing a clear signature for HNO$_3$; the feature at 11.25 $μ$m is particularly promising. Partition functions plus full line lists of transitions are made available in an electronic form as supplementary data to the article and at www.exomol.com.

astro-ph.EP↗

arXiv2015

ExoMol molecular line lists XII: Line Lists for 8 isotopologues of CS

Comprehensive vibration-rotation line lists for eight isotopologues of carbon monosulphide (CS) ($^{12}$C$^{32}$S, $^{12}$C$^{33}$S, $^{12}$C$^{34}$S, $^{12}$C$^{36}$S, $^{13}$C$^{32}$S, $^{13}$C$^{33}$S, $^{13}$C$^{34}$S, $^{13}$C$^{36}$S) in their ground electronic states are calculated. These line lists are suitable for temperatures up to 3000 K. A spectroscopically-determined potential energy curve (PEC) and dipole moment curve (DMC) are taken from literature. This PEC is adapted to suit our method prior to the computation of ro-vibrational energies. The calculated energies are then substituted by experimental energies, where available, to improve the accuracy of the line lists. The {\it ab initio} DMC is used without refinement to generate Einstein A coefficients. Full line lists of vibration-rotation transitions and partition functions are made available in an electronic form as supporting information to this paper and at \url{www.exomol.com}.

astro-ph.GA↗

arXiv2015

ExoMol line lists VIII: A variationally computed line list for hot formaldehyde

A computed line list for formaldehyde, H$_2{}^{12}$C$^{16}$O, applicable to temperatures up to $T=1500$~K is presented. An empirical potential energy and {\it ab initio} dipole moment surfaces are used as the input to nuclear motion program TROVE. The resulting line list, referred to as \textit{AYTY}, contains 10.3 million rotational-vibrational states and around 10 billion transition frequencies. Each transition includes associated Einstein-$A$ coefficients and absolute transition intensities, for wavenumbers below 10~000 cm$^{-1}$ and rotational excitations up to $J=70$. Room-temperature spectra are compared with laboratory measurements and data currently available in the HITRAN database. These spectra show excellent agreement with experimental spectra and highlight the gaps and limitations of the HITRAN data. The full line list is available from the CDS database as well as at \url{www.exomol.com}.

astro-ph.GA↗

arXiv2015

ExoMol molecular line lists X: The spectrum of sodium hydride

Accurate and complete rotational, rotational-vibrational and rotational-vibrational-electronic line lists are calculated for sodium hydride: both the NaH and NaD isotopologues are considered. These line lists cover all ro-vibrational states of the ground ($X$~$^1Σ^+$) and first excited ($A$~$^1Σ^+$) electronic states. The calculations use available spectroscopically-determined potential energy curves and new high-quality, \textit{ab initio} dipole moment curves. Partition functions for both isotopologues are calculated and the effect of quasibound states is considered. The resulting line lists are suitable for temperatures up to about 7000~K and are designed for studies of exoplanet atmospheres, brown dwarfs and cool stars. In particular, the NaH $A-X$ band is found to show a broad absorption feature at about 385 nm which should provide a signature for the molecule. All partition functions, lines and transitions are available as Supplementary Information to this article and at \url{www.exomol.com}.

astro-ph.GA↗

arXiv2015

Accurate Prediction of the Ammonia Probes of a Variable Proton-to-Electron Mass Ratio

A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of $^{14}$NH$_3$, $^{15}$NH$_3$, $^{14}$ND$_3$, and $^{15}$ND$_3$ is carried out variationally using the TROVE approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coefficients. Particular attention is paid to the $Δk=\pm 3$ transitions between the accidentally coinciding rotation-inversion energy levels of the $ν_2=0^+,0^-,1^+$ and $1^-$ states, and the inversion transitions in the $ν_4=1$ state affected by the "giant" $l$-type doubling effect. These transitions exhibit highly anomalous sensitivities, thus appearing as promising probes of a possible cosmological variation of the proton-to-electron mass ratio $μ$. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection.

astro-ph.CO↗

arXiv2015

The calculated rovibronic spectrum of scandium hydride, ScH

The electronic structure of six low-lying electronic states of scandium hydride, $X\,{}^{1}Σ^+$, $a\,{}^{3}Δ$, $b\,{}^{3}Π$, $A\,{}^{1}Δ$ $c\,{}^{3}Σ^+$, and $B\,{}^{1}Π$, is studied using multi-reference configuration interaction as a function of bond length. Diagonal and off-diagonal dipole moment, spin-orbit coupling and electronic angular momentum curves are also computed. The results are benchmarked against experimental measurements and calculations on atomic scandium. The resulting curves are used to compute a line list of molecular ro-vibronic transitions for $^{45}$ScH.

astro-ph.GA↗

arXiv2015

ExoMol molecular line lists: IX The spectrum of AlO

Accurate line lists are calculated for aluminium monoxide covering the pure rotation, rotation-vibration and electronic (B -- X blue-green and A -- X infrared bands) spectrum. Line lists are presented for the main isotopologue, $^{27}$Al$^{16}$O, as well as for $^{27}$Al$^{17}$O, $^{27}$Al$^{18}$O and $^{26}$Al$^{16}$O. These line lists are suitable for high temperatures (up to 8000 K) including those relevant to exoplanetary atmospheres and cool stars. A combination of empirical and \textit{ab initio} methods is used: the potential energy curves were previously determined to high accuracy by fitting to extensive data from analysis of laboratory spectra; a high quality {\it ab initio} dipole moment curve is calculated using quadruple zeta basis set and the multi-reference configuration interaction (MRCI) method. Partition functions plus full line lists of transitions are made available in an electronic form as supplementary data to this article and at \url{www.exomol.com}.

astro-ph.GA↗

arXiv2015

Exomol molecular line lists VI: A high temperature line list for Phosphorus Nitride

Accurate rotational-vibrational line lists for $^{31}$P$^{14}$N and $^{31}$P$^{15}$N in their ground electronic states are computed. The line lists are produced using an empirical potential energy curve obtained by fitting to the experimental transition frequencies available in the literature in conjunction with an accurate, high level \textit{ab initio} dipole moment curve. In these calculations the programs DPotFit and LEVEL~8.0 were used. The new line lists reproduce the experimental wavenumbers with a root-mean-square error of 0.004~cm$^{-1}$. The line lists cover the frequency range 0--51000 cm$^{-1}$, contain almost 700~000 lines each and extend up to a maximum vibrational level of $v$=66 and a maximum rotational level of $J$=357. They should be applicable for a large range of temperature up to, at least, 5000~K. These new line lists are used to simulate spectra for PN at a range of temperatures and are deposited in the Strasbourg data centre. This work is performed as part of the ExoMol project.

astro-ph.GA↗

arXiv2015

Methane and Ammonia in the near-infrared spectra of late T dwarfs

Analysis of T dwarfs using model atmospheres has been hampered by the absence of reliable line lists for methane and ammonia. Newly computed high temperature line lists for both of these important molecules are now available, so it is timely to investigate the appearance of the various absorption features in T dwarfs in order to better understand their atmospheres and validate the new line lists. We present high quality R~5000 Gemini/NIFS 1.0-2.4 microns spectra of the T8 standard 2MASS 0415-0935 and the T9 standard UGPS 0722-0540. We use these spectra to identify numerous methane and ammonia features not previously seen and we discuss the implications for our understanding of T dwarf atmospheres. Among our results, we find that ammonia is the dominant opacity source between ~1.233-1.266 microns in UGPS 0722-0540, and we tentatively identify several absorption features in this wavelength range in the T9's spectrum which may be due entirely to ammonia opacity. Our results also suggest that water rather than methane is the dominant opacity source in the red half of the J-band of the T8 dwarf. Water appears to be the main absorber in this wavelength region in the T9 dwarf until ~1.31 microns, when methane starts to dominate.

astro-ph.SR↗

arXiv2015

A theoretical room-temperature line list for 15NH3

A new room temperature line list for $^{15}$NH$_3$ is presented. This line list comprised of transition frequencies and Einstein coefficients has been generated using the `spectroscopic' potential energy surface NH3-Y2010 and an ab initio dipole moment surface. The $^{15}$NH$_3$ line list is based on the same computational procedure used for the line list for $^{14}$NH$_3$ BYTe reported recently and should be as accurate. Comparisons with experimental frequencies and intensities are presented. The synthetic spectra show excellent agreement with experimental spectra.

astro-ph.EP↗