arXiv subjects

Jonathan Tennyson

Publications and source records attributed to Jonathan Tennyson.

At least 73 records · Page 4Linked to original sources

arXiv2022

Cross-sections for heavy atmospheres: H$_2$O continuum

Most of the exoplanets detected up to now transit in front of their host stars, allowing for the generation of transmission spectra; the study of exoplanet atmospheres relies heavily upon accurate analysis of these spectra. Recent discoveries mean that the study of atmospheric signals from low-mass, temperate worlds are becoming increasingly common. The observed transit depth in these planets is small and more difficult to analyze. Analysis of simulated transmission spectra for two small, temperate planets (GJ 1214 b and K2-18 b) is presented, giving evidence for significant differences in simulated transit depth when the water vapor continuum is accounted for when compared to models omitting it. These models use cross-sections from the CAVIAR lab experiment for the water self-continuum up to 10,000 cm$^{-1}$; these cross-sections exhibit an inverse relationship with temperature, hence lower-temperature atmospheres are the most significantly impacted. Including the water continuum strongly affects transit depths, increasing values by up to 80 ppm, with the differences for both planets being detectable with the future space missions Ariel and JWST. It is imperative that models of exoplanet spectra move toward adaptive cross-sections, increasingly optimized for H$_2$O-rich atmospheres. This necessitates including absorption contribution from the water vapor continuum into atmospheric simulations.

astro-ph.EP↗

arXiv2022

Cross-sections for heavy atmospheres: H$_2$O self-broadening

The discovery of super-Earth and mini-Neptune exoplanets means that atmospheric signals from low-mass, temperate exoplanets are being increasingly studied. The signal acquired as the planet transits its host star, known as the transit depth, is smaller for these planets and, as such, more difficult to analyze. The launch of the space telescopes James Webb (JWST) & Ariel will give rise to an explosion in the quality and quantity of spectroscopic data available for an unprecedented number of exoplanets in our galaxy. Accurately extracting the information content, thereby permitting atmospheric science, of such data-sets will require robust models and techniques. We present here the analysis of simulated transmission spectra for water-rich atmospheres, giving evidence for non-negligible differences in simulated transit depths when self-broadening of H$_2$O is correctly accounted for, compared with the currently typically accepted standard of using H$_2$ and He-broadened cross-sections. Our case-study analysis is carried out on two super-Earths, focusing on water-based atmospheres, ranging from H$_2$-rich to H$_2$O-rich. The transit depth is considerably affected, increasing values by up to 60 ppm, which is shown to be detectable with JWST and Ariel. The differences are most pronounced for the lighter (i.e. $mu$ $\sim$ 4) atmospheres. Our work illustrates that it is imperative that the field of exoplanet spectroscopy moves toward adapted cross-sections, increasingly optimized for high-mu atmospheres for studies of super-Earths and mini-Neptunes.

astro-ph.EP↗

arXiv2022

A method for the variational calculation of hyperfine-resolved rovibronic spectra of diatomic molecules

An algorithm for the calculation of hyperfine structure and spectra of diatomic molecules based on the variational nuclear motion is presented. Hyperfine coupling terms considered are Fermi-contact, nuclear spin-electron spin dipole-dipole, nuclear spin-orbit, nuclear spin-rotation and nuclear electric quadrupole interactions. Initial hyperfine-unresolved wavefunctions are obtained for given set of potential energy curves and associated couplings by variation solution of the nuclear-motion Schrödinger equation. Fully hyperfine-resolved parity-conserved rovibronic Hamiltonian matrices for a given final angular momentum, $\bm{F}$, are constructed and then diagonalized to give hyperfine-resolved energies and wavefunctions.Electric transition dipole moment curves can then be used to generate a hyperfine-resolved line list by applying rigorous selection rules.The algorithm is implemented in \textsc{Duo}, which is a general program for calculating spectra of diatomic molecules. This approach is tested for NO and MgH,and the results are compared to experiment and shown to be consistent with those given the well-used effective Hamiltonian code PGOPHER.

physics.chem-ph↗

arXiv2021

ExoMol molecular line lists -- XLIII: Rovibronic molecular line list the low-lying two states of NaO

The sodium monoxide radical (NaO) is observed in night glow in the Earth's mesosphere and likely has astronomical importance. This study concerns the optical transitions within the ground X $^2Π$ state and to the very low-lying ($T_{\textrm e}\approx 2000$ cm$^{-1}$) excited A $^2Σ^+$ state. A line list consisting of rovibronic term values, allowed electric dipole transitions, Einstein coefficients, and partition functions for varying temperature are produced due to a variational solution of the coupled-channel Schrödinger equations using the program \Duo. MRCI \textit{ab initio} calculations characterising the potential energy curves of the both states, spin-orbit and $L$-uncoupling non-adiabatic matrix elements, as well as permanent and transition dipole moments were integral in formation of the final deperturbation model. \textit{Ab initio} potential energy curves are represented in the analytical Extended-Morse-Oscillator form and refined, along with the spin-orbit and $L$-uncoupling functions, by least-squares fitting to the available spectroscopic data. The input experimental data consisted of pure rotational transitions within the fine structure components of the X $^2Π$ state for $v''\in [0,3]$ vibrational levels as well as the rovibronic A $^2Σ^+(v'=0) \leftarrow$ X $^2Π(v''=0)$ transitions, both with limited coverage over rotational excitation. The lack of data detailing the vibrational structure of the X and A states prompts a request for further experimental study of higher excited levels which would provide a robust spectroscopic model. The NaO NaOUCMe line list is available via www.exomol.com and the CDS database.

physics.chem-ph↗

arXiv2021

ExoMol line lists -- XLIV. IR and UV line list for silicon monoxide (SiO)

A new silicon monoxide ($^{28}$Si$^{16}$O) line list covering infrared, visible and ultraviolet regions called SiOUVenIR is presented. This line list extends the infrared EBJT ExoMol line list by including vibronic transitions to the $A\,{}^{1}Π$ and $E\,{}^{1}Σ^{+}$ electronic states. Strong perturbations to the $A\,{}^{1}Π$ band system are accurately modelled through the treatment of 6 dark electronic states: $C\,{}^{1}Σ^{-}$, $D\,{}^{1}Δ$, $a\,{}^{3}Σ^{+}$, $b\,{}^{3}Π$, $e\,{}^{3}Σ^{-}$ and $d\,{}^{3}Δ$. Along with the $X\,{}^{1}Σ^{+}$ ground state, these 9 electronic states were used to build a comprehensive spectroscopic model of SiO using a combination of empirical and ab initio curves, including the potential energy (PE), spin-orbit (SO), electronic angular momentum (EAM) and (transition) dipole moment curves. The ab initio PE and coupling curves, computed at the multireference configuration interaction (MRCI) level of theory, were refined by fitting their analytical representations to 2617 experimentally derived SiO energy levels determined from 97 vibronic bands belonging to the $X$-$X$, $E$-$X$ and $A$-$X$ electronic systems through the MARVEL procedure. 112 observed forbidden transitions from the $C$-$X$, $D$-$X$, $e$-$X$, and $d$-$X$ bands were assigned using our predictions, and these could be fed back into the MARVEL procedure. The SiOUVenIR line list was computed using published ab initio transition dipole moments for the $E$-$X$ and $A$-$X$ bands; the line list is suitable for temperatures up to 10,000 K and for wavelengths longer than 140 nm. SiOUVenIR is available from www.exomol.com and the CDS database.

astro-ph.EP↗

arXiv2021

Rovibronic spectroscopy of PN from first principles

We report an ab initio study on the rovibronic spectroscopy of the closed-shell diatomic molecule phosphorous mononitride, PN. The study considers the nine lowest electronic states, $X\,{}^{1}Σ^{+}$, $A\,{}^{1}Π$, $C\,{}^{1}Σ^{-}$, $D\,{}^{1}Δ$, $E\,{}^{1}Σ^{-}$, $a\,{}^{3}Σ^{+}$, $b\,{}^{3}Π$, $d\,{}^{3}Δ$ and $e\,{}^{3}Σ^{-}$ using high level electronic structure theory and accurate nuclear motion calculations. The ab initio data cover 9 potential energy, 14 spin-orbit coupling, 7 electronic angular momentum coupling, 9 electric dipole moment and 8 transition dipole moment curves. The Duo nuclear motion program is used to solve the coupled nuclear motion Schrödinger equations for these nine electronic states and to simulate rovibronic absorption spectra of $^{31}$P$^{14}$N for different temperatures, which are compared to available spectroscopic studies. Lifetimes for all states are calculated and compared to previous results from the literature. The calculated lifetime of the $A\,{}^{1}Π$ state shows good agreement with an experimental value from the literature, which is an important quality indicator for the ab initio $A$-$X$ transition dipole moment.

physics.atom-ph↗

arXiv2021

A high-resolution line list for AlO

Indications of aluminium monoxide in atmospheres of exoplanets are being reported. Studies using high-resolution spectroscopy should allow a strong detection but require high accuracy laboratory data. A \textsc{marvel} (measured active rotational-vibrational energy levels) analysis is performed for the available spectroscopic data on $^{27}$Al$^{16}$O: 22\,473 validated transitions are used to determine 6\,485 distinct energy levels. These empirical energy levels are used to provide an improved, spectroscopically accurate version of the ExoMol ATP line list for $^{27}$Al$^{16}$O; at the same time the accuracy of the line lists for the isotopically-substituted species $^{26}$Al$^{16}$O, $^{27}$Al$^{17}$O and $^{27}$Al$^{18}$O are improved by correcting levels in line with the corrections used for $^{27}$Al$^{16}$O. These line lists are available from the ExoMol database at http://www.exomol.com.

astro-ph.EP↗

arXiv2021

A spectroscopic model for the low-lying electronic states of NO

The rovibronic structure of A$^2Σ^+$, B$^2Π$ and C$^2Π$ states of nitric oxide (NO)is studied with the aim of producing comprehensive line lists for its near ultraviolet spectrum. Empirical energy levels for the three electronic states are determined using the a combination of the empirical MARVEL procedure and ab initio calculations, and the available experimental data are critically evaluated. Abinito methods which deal simultaneously with the Rydberg-like A$^2Σ^+$ and C$^2Π$, and the valence B$^2Π$ state are tested. Methods of modeling the sharp avoided crossing between the B$^2Π$ and C$^2Π$ states are tested. A rovibronic Hamiltonian matrix is constructed using variational nuclear motion program DUO whose eigenvalues are fitted to the MARVEL energy levels. The matrix also includes coupling terms obtained from the refinement of the ab initio potential energy and spin-orbit coupling curves. Calculated and observed energy levels agree well with each other, validating the applicability of our method and providing a useful model for this open shell system.

physics.chem-ph↗

arXiv2021

ExoMol molecular line lists -- XLII: Rovibronic molecular line list for the low-lying states of NO

An accurate line list, called XABC, is computed for nitric oxide which covers its pure rotational, vibrational and rovibronic spectra. A mixture of empirical and theoretical electronic transition dipole moments are used for the final calculation of $^{14}\mathrm{N}^{16}\mathrm{O}$ rovibronic $\mathrm{A}\,^2Σ^+$ -- $\mathrm{X}\,^2Π$, $\mathrm{B}\,^2Π$ -- $\mathrm{X}^2Π$ and $\mathrm{C}\,^2Π$ -- $\mathrm{X}\,^2Π$ which correspond to the $γ$, $β$ and $δ$ band systems, respectively, as well as minor improvements to transitions within the $\mathrm{X}\,^2Π$ ground state. The work is a major update of the ExoMol NOname line list. It provides a high-accuracy NO ultraviolet line list covering the complicated regions where the $\mathrm{B}\,^2Π$-$\mathrm{C}\,^2Π$ states interact. XABC provides comprehensive data for the lowest four doublet states of NO in the region of $λ> 160 ~ \mathrm{nm}$ ($\tildeν < 63~000~\mathrm{cm}^{-1}$) for the analysis of atmospheric NO on Earth, Venus or Mars, other astronomical observations and applications. The data is available via www.exomol.com.

astro-ph.EP↗

arXiv2021

Highly accurate HF dimer ab initio potential energy surface

A very accurate, (HF)$_2$ potential energy surface (PES) is constructed based on \ai\ calculations performed using the MOLPRO package at the CCSD(T) level of theory with an aug-cc-pvQz-F12 basis set at about 161~000 points. a higher correlation correction is computed at CCSDT(Q) level for 2000 points and is considered alongside other more minor corrections due to relativity, core-valence correlation and Born-Oppenheimer failure. The analytical surface constructed uses 500 constants to reproduce the \ai\ points with a standard deviation of 0.3 \cm. Vibration-rotation-inversion energy levels of the HF dimer are computed for this PES by variational solution of the nuclear-motion Schrödinger using program WAVR4. Calculations over an extended range of rotationally excited states show very good agreement with the experimental data. In particular the known empirical rotational constants $B$ for the ground vibrational states are predicted to better than about 2 MHz. $B$ constants for excited vibrational states are reproduced several times more accurately than by previous calculations. The experimental dissociation energy of the HF dimer is reproduced \ai\ within the experimental accuracy of about 1 \cm\ for the first time. This level of accuracy is shown to extend to higher excited inter-molecular vibrational states $v$ and higher excited rotational quantum numbers $(J,K_a)$.

physics.atm-clus↗

arXiv2021

Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)

The rovibronic (rotation-vibration-electronic) spectrum of the calcium monohydroxide radical (CaOH) is of interest to studies of exoplanet atmospheres and ultracold molecules. Here, we theoretically investigate the $\tilde{A}\,^2Π$--$\tilde{X}\,^2Σ^+$ band system of CaOH using high-level \textit{ab initio} theory and variational nuclear motion calculations. New potential energy surfaces (PESs) are constructed for the $\tilde{X}\,^2Σ^+$ and $\tilde{A}\,^2Π$ electronic states along with $\tilde{A}$--$\tilde{X}$ transition dipole moment surfaces (DMSs). For the ground $\tilde{X}\,^2Σ^+$ state, a published high-level \textit{ab initio} PES is empirically refined to all available experimental rovibrational energy levels up to $J=15.5$, reproducing the observed term values with a root-mean-square (rms) error of 0.06~cm$^{-1}$. Large-scale multireference configuration interaction (MRCI) calculations using quintuple-zeta quality basis sets are employed to generate the $\tilde{A}\,^2Π$ state PESs and $\tilde{A}$--$\tilde{X}$ DMSs. Variational calculations consider both Renner-Teller and spin-orbit coupling effects, which are essential for a correct description of the spectrum of CaOH. Computed rovibronic energy levels of the $\tilde{A}\,^2Π$ state, line list calculations up to $J=125.5$, and an analysis of Renner-Teller splittings in the $ν_2$ bending mode of CaOH are discussed.

physics.chem-ph↗

arXiv2021

Determination of approximate quantum labels based on projections of the total angular momentum on the molecule-fixed axis

Molecular line lists, particularly those computed for high temperature applications, often have very few states assigned local quantum numbers. These are often important components for accurately determining line shape parameters required for radiative transfer simulations. The projection of the total angular momentum onto the molecule fixed axis ($k$) is investigated in the Radau internal coordinate system to determine when it can be considered a good quantum number. In such a coordinate system, when the square of the $k^{th}$ component of the wavefunction is greater than one half, then we can classify $k$ as a good quantum number in accordance with the theorem of Hose and Taylor. Furthermore, it is demonstrated that when this holds true, oblate and prolate quantum labels $K_{a}$ and $K_{c}$ can reliably be predicted. This is demonstrated for the water and ozone molecules.

physics.chem-ph↗

arXiv2021

Electric quadrupole transitions in carbon dioxide

Recent advances in the high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe for the first time very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here we present accurate theoretical predictions of the complete quadrupole ro-vibrational spectrum of a non-polar molecule CO$_2$, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars ACS MIR spectroscopic observations of the martian atmosphere. Predicted quadrupole transitions appear in some of the mid-infrared CO$_2$ and water vapor transparency regions, making them important for detection and characterization of the minor absorbers in water- and CO$_2$-rich environments, such as present in the atmospheres of Earth, Venus and Mars.

physics.atom-ph↗

arXiv2021

Reduced Density Matrix Sampling: Self-consistent Embedding and Multiscale Electronic Structure on Current Generation Quantum Computers

We investigate fully self-consistent multiscale quantum-classical algorithms on current generation superconducting quantum computers, in a unified approach to tackle the correlated electronic structure of large systems in both quantum chemistry and condensed matter physics. In both of these contexts, a strongly correlated quantum region of the extended system is isolated and self-consistently coupled to its environment via the sampling of reduced density matrices. We analyze the viability of current generation quantum devices to provide the required fidelity of these objects for a robust and efficient optimization of this subspace. We show that with a simple error mitigation strategy and optimization of compact tensor product bases to minimize the number of terms to sample, these self-consistent algorithms are indeed highly robust, even in the presence of significant noises on quantum hardware. Furthermore, we demonstrate the use of these density matrices for the sampling of non-energetic properties, including dipole moments and Fermi liquid parameters in condensed phase systems, achieving a reliable accuracy with sparse sampling. It appears that uncertainties derived from the iterative optimization of these subspaces is smaller than variances in the energy for a single subspace optimization with current quantum hardware. This boosts the prospect for routine self-consistency to improve the choice of correlated subspaces in hybrid quantum-classical approaches to electronic structure for large systems in this multiscale fashion.

quant-ph↗

arXiv2021

HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres

Computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. Since the underlying spectroscopic line lists are constantly expanding and currently include up to ~ 10^10 - 10^11 transition lines, the opacity calculator codes need to become more powerful. Here we present major upgrades to the HELIOS-K GPU-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. Besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets: from downloading and pre-processing the data to performing the opacity calculations in a user-friendly way. HELIOS-K supports line lists from ExoMol, HITRAN, HITEMP, NIST, Kurucz and VALD3. By matching the resolution of 0.1 cm^-1 and cutting length of 25 cm^-1 used by the ExoCross code for timing performance (251 seconds excluding data read-in time), HELIOS-K can process the ExoMol BT2 water line list in 12.5 seconds. Using a resolution of 0.01 cm^-1, it takes 45 seconds - equivalent to about 10^7 lines per second. As a wavenumber resolution of 0.01 cm^-1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species, and make them freely available on the open-access DACE database. For the opacity calculations of the database, we use a cutting length of 100 cm^-1 for molecules and no cutting length for atoms. Our opacities are available for downloading from https://dace.unige.ch/opacityDatabase and may be visualized using https://dace.unige.ch/opacity.

astro-ph.EP↗

arXiv2021

An improved rovibrational linelist of formaldehyde, \spec{h212c16o}

Published high-resolution rotation-vibration transitions of \spec{h212c16o}, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, $ν_3$, $ν_4$, and $ν_6$ vibrational states. Of the \nbNonRedTr\ non-redundant transitions processed, which come from \nbSr\ sources including the present work, \nbValTr\ could be validated, providing \nbEl\ empirical energy levels of \spec{h212c16o}\ with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol's AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material.

astro-ph.SR↗

arXiv2020

An update to the MARVEL dataset and ExoMol line list for 12C2

The spectrum of dicarbon (C2) is important in astrophysics and for spectroscopic studies of plasmas and flames. The C2 spectrum is characterized by many band systems with new ones still being actively identified; astronomical observations involve eight of these bands. Recently, Furtenbacher et al. (2016, Astrophys. J. Suppl., 224, 44) presented a set of 5699 empirical energy levels for 12C2, distributed among 11 electronic states and 98 vibronic bands, derived from 42 experimental studies and obtained using the MARVEL (Measured Active Rotational-Vibrational Energy Levels) procedure. Here, we add data from 13 new sources and update data from 5 sources. Many of these data sources characterize high-lying electronic states, including the newly detected 3Pig state. Older studies have been included following improvements in the MARVEL procedure which allow their uncertainties to be estimated. These older works in particular determine levels in the C1Pig state, the upper state of the insufficiently characterized Deslandres-d'Azambuja (C1Pig-A1Piu) band. The new compilation considers a total of 31323 transitions and derives 7047 empirical(MARVEL) energy levels spanning 20 electronic and 142 vibronic states. These new empirical energy levels are used here to update the 8states C2 ExoMol line list. This updated line list is highly suitable for high-resolution cross-correlation studies in astronomical spectroscopy of, for example, exoplanets, as 99.4% of the transitions with intensities over 10^(-18) cm/molecule at 1000 K have frequencies determined by empirical energy levels.

astro-ph.EP↗

arXiv2020

The ExoMolOP Database: Cross-sections and k-tables for Molecules of Interest in High-Temperature Exoplanet Atmospheres

A publicly available database of opacities for molecules of astrophysical interest, ExoMolOP, has been compiled for over 80 species, based on the latest line list data from the ExoMol, HITEMP and MoLLIST databases. These data are generally suitable for characterising high temperature exoplanet or cool stellar/substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room-temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS and petitRADTRANS, and include both cross-sections (at R~=~$\fracλ{Δλ}$~=~15,000) and k-tables (at R~=~$\fracλ{Δλ}$~=~1000) for the 0.3~-~50$μ$m wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or from those for a known molecule with similar molecular properties where no broadening data are available. The data are available from www.exomol.com.

astro-ph.EP↗