Showing papers by "Jonathan Tennyson published in 2014"

ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K

Abstract: A new hot line list is calculated for 12 CH4 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 µm and includes all transitions to upper states with energies below hc · 18 000 cm −1 and rotational excitation up to J = 39. The line list is computed using the eigenvalues and eigenfunctions of CH4 obtained by variational solution of the Schr¨ odinger equation for the rotation–vibration motion of nuclei employing program TROVE and a new ‘spectroscopic’ potential energy surface (PES) obtained by refining an ab initio PES (CCSD(T)-F12c/aug-cc-pVQZ) through least-squares fitting to the experimentally derived energies with J = 0−4 and a previously reported ab initio dipole moment surface (CCSD(T)F12c/aug-cc-pVTZ). 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. The 10to10 line list is suitable for modelling atmospheres of cool stars and exoplanets. It is available from the CDS data base as well as at www.exomol.com.

Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)

Abstract: The report of an IUPAC Task Group, formed in 2011 on "Intensities and line shapes in high-resolu- tion spectra of water isotopologues from experiment and theory" (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational- rotational and pure rotational transitions of the water molecule have resulted in the development of a variety

ExoMol line lists - III. An improved hot rotation-vibration line list for HCN and HNC

Abstract: A revised rotation-vibration line list for the combined hydrogen cyanide (HCN)/ hydrogen isocyanide (HNC) system is presented. The line list uses ab initio transi-tion intensities calculated previously (Harris et al., ApJ, 2002, 578, 657) and extensivedatasets of recently measured experimental energy levels (Mellau, J. Chem. Phys. andJ. Mol. Spectrosc. 2010-2011). The resulting line list has signi cantly more accuratewavelengths than previous ones for these systems. An improved value for the sepa-ration between HCN and HNC is adopted leading to an approximately 25 % lowerpredicted thermal population of HNC as a function of temperature in the key 2000 to3000 K region. Temperature-dependent partition functions and equilibrium constantsare presented. The line lists are validated by comparison with laboratory spectra andare presented in full as supplementary data to the article and at www.exomol.com.Key words: molecular data; opacity; astronomical data bases: miscellaneous; planetsand satellites: atmospheres; stars: low-mass

Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)

Abstract: The report of an IUPAC Task Group, formed in 2011 on "Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory" (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule have resulted in the development of a variety of alternative line-profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially Correlated quadratic-Speed-Dependent Hard-Collision profile should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann--Tran profile (HTP). The HTP is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions.

Tau-REx I: A next generation retrieval code for exoplanetary atmospheres

Abstract: Spectroscopy of exoplanetary atmospheres has become a well established method for the characterisation of extrasolar planets. We here present a novel inverse retrieval code for exoplanetary atmospheres. TauRex (Tau Retrieval for Exoplanets) is a line-by-line radiative transfer fully Bayesian retrieval framework. TauRex includes the following features: 1) the optimised use of molecular line-lists from the Exomol project; 2) an unbiased atmospheric composition prior selection, through custom built pattern recognition software; 3) the use of two independent algorithms to fully sample the Bayesian likelihood space: nested sampling as well as a more classical Markov Chain Monte Carlo approach; 4) iterative Bayesian parameter and model selection using the full Bayesian Evidence as well as the Savage-Dickey Ratio for nested models, and 5) the ability to fully map very large parameter spaces through optimal code parallelisation and scalability to cluster computing. In this publication we outline the TauRex framework and demonstrate, using a theoretical hot-Jupiter transmission spectrum, the parameter retrieval and model selection. We investigate the impact of Signal-to-Noise and spectral resolution on the retrievability of individual model parameters, both in terms of error bars on the temperature and molecular mixing ratios as well as its effect on the model's global Bayesian evidence.

Spectrum of hot methane in astronomical objects using a comprehensive computed line list.

Abstract: Hot methane spectra are important in environments ranging from flames to the atmospheres of cool stars and exoplanets. A new spectroscopic line list, 10to10, for 12CH4 containing almost 10 billion transitions is presented. This comprehensive line list covers a broad spectroscopic range and is applicable for temperatures up to 1,500 K. Previous methane data are incomplete, leading to underestimated opacities at short wavelengths and elevated temperatures. Use of 10to10 in models of the bright T4.5 brown dwarf 2MASS 0559-14 leads to significantly better agreement with observations and in studies of the hot Jupiter exoplanet HD 189733b leads to up to a 20-fold increase in methane abundance. It is demonstrated that proper inclusion of the huge increase in hot transitions which are important at elevated temperatures is crucial for accurate characterizations of atmospheres of brown dwarfs and exoplanets, especially when observed in the near-infrared.

IUPAC critical evaluation of the rotational–vibrational spectra of water vapor. Part IV. Energy levels and transition wavenumbers for D216O, D217O, and D218O

Abstract: This paper is the fourth of a series of papers reporting critically evaluated rotational–vibrational line positions, transition intensities, pressure dependences, and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. This paper presents energy level and transition data for the following doubly and triply substituted isotopologues of water: D216O, D217O, and D218O. The MARVEL (Measured Active Rotational–Vibrational Energy Levels) procedure is used to determine the levels, the lines, and their self-consistent uncertainties for the spectral regions 0–14 016, 0–7969, and 0–9108 cm−1 for D216O, D217O, and D218O, respectively. For D216O, D217O, and D218O, 53 534, 600, and 12 167 lines are considered, respectively, from spectra recorded in absorption at room temperature and in emission at elevated temperatures. The number of validated energy levels is 12 269, 338, and 3351 for D216O, D217O, and D218O, respectively. The energy levels have been checked against the ones determined, with an average accuracy of about 0.03 cm−1, from variational rovibrational computations employing exact kinetic energy operators and an accurate potential energy surface. Furthermore, the rovibrational labels of the energy levels have been validated by an analysis of the computed wavefunctions using the rigid-rotor decomposition (RRD) scheme. The extensive list of MARVEL lines and levels obtained is deposited in the Supplementary Material of this paper, in a distributed information system applied to water, W@DIS, and on the official MARVEL website, where they can easily be retrieved.

A database of water transitions from experiment and theory (IUPAC Technical Report)

Abstract: The report and results of an IUPAC Task Group (TG) formed in 2004 on "A Database of Water Transitions from Experiment and Theory" (Project No. 2004-035-1-100) are presented. Energy levels and recommended labels involving exact and approximate quantum numbers for the main isotopologues of water in the gas phase, H2 16O, H2 18O, H2 17O, HD16O, HD18O, HD17O, D2 16O, D2 18O, and D2 17O, are determined from measured transition frequencies. The transition frequencies and energy levels are validated using first-principles nuclear motion computations and the MARVEL (measured active rotational-vibrational energy levels) approach. The extensive data including lines and levels are required for analysis and synthesis of spectra, thermochemical applications, the construction of theoretical models, and the removal of spectral contamination by ubiquitous water lines. These datasets can also be used to assess where measurements are lacking for each isotopologue and to provide accurate frequencies for many yet-to-be measured transitions. The lack of high-quality frequency calibration standards in the near infrared is identified as an issue that has hindered the determination of high-accuracy energy levels at higher frequencies. The generation of spectra using the MARVEL energy levels combined with transition intensities computed using high accuracy ab initio dipole moment surfaces are discussed. A recommendation of the TG is for further work to identify a single, suitable model to represent pressure-(and temperature-)dependent line profiles more accurately than Voigt profiles.

IUPAC Technical report

Abstract: The report and results of an IUPAC Task Group (TG) formed in 2004 on "A Database of Water Tran- sitions from Experiment and Theory" (Project No. 2004-035-1-100) are presented. Energy levels and recom- mended labels involving exact and approximate quantum numbers for the main isotopologues of water in the gas phase, H 2 16 O, H 2 18 O, H 2 17 O, HD 16 O, HD 18 O, HD 17 O, D 2 16 O, D 2 18 O, and D 2 17 O, are determined from meas- ured transition frequencies. The transition frequencies and energy levels are validated using first-princi- ples nuclear motion computations and the MARVEL (measured active rotational-vibrational energy levels) approach. The extensive data including lines and levels are required for analysis and synthesis of spectra, thermochemical applications, the construction of theoretical models, and the removal of spectral contamina- tion by ubiquitous water lines. These datasets can also be used to assess where measurements are lacking for each isotopologue and to provide accurate frequencies for many yet-to-be measured transitions. The lack of high-quality frequency calibration standards in the near infrared is identified as an issue that has hindered the determination of high-accuracy energy levels at higher frequencies. The generation of spectra using the MARVEL energy levels combined with transition intensities computed using high accuracy ab initio dipole moment surfaces are discussed. A recommendation of the TG is for further work to identify a single, suitable model to represent pressure- (and temperature-) dependent line profiles more accurately than Voigt profiles.

High temperature partition functions and thermodynamic data for ammonia and phosphine

Abstract: The total internal partition function of ammonia ( 14 NH 3 ) and phosphine ( 31 PH 3 ) are calculated as a function of temperature by explicit summation of 153 million (for PH 3 ) and 7.5 million (for NH 3 ) theoretical rotation-vibrational energy levels. High accuracy estimates are obtained for the specific heat capacity, C p , the Gibbs enthalpy function, gef , the Helmholtz function, hcf , and the entropy, S , of gas phase molecules as a function of temperature. In order to reduce the computational costs associated with the high rotational excitations, only the A -symmetry energy levels are used above a certain threshold of the total angular momentum number J . With this approach levels are summed up to dissociation energy for values of J max =45 and 100 for ammonia ( E max =41 051 cm −1 ) and phosphine ( E max =28 839.7 cm −1 ), respectively. Estimates of the partition function are converged for all temperatures considered for phosphine and below 3000 K for ammonia. All other thermodynamic properties are converged to at least 2000 K for ammonia and fully converged for phosphine.

Electron-impact resonant vibrational excitation and dissociation processes involving vibrationally excited N 2 molecules

Abstract: Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron–N2 collisions occurring through the resonant state are reviewed. New calculations are performed using accurate potential energy curves for the N2 electronic ground state, taken from the literature, and for the resonant state, obtained from R-matrix calculations. The calculations are extended to resonant excitation processes involving the N2 ground state vibrational continuum, leading to dissociation. Electron-impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided. The behavior of the dissociative cross sections is investigated for rotationally excited N2 molecules, with J = 50, 100 and 150, and for different vibrational levels.

ExoMol molecular line lists V: the ro-vibrational spectra of NaCl and KCl

Abstract: Accurate rotation–vibration line lists for two molecules, NaCl and KCl, in their ground electronic states are presented. These line lists are suitable for temperatures relevant to exoplanetary atmospheres and cool stars (up to 3000K). Isotopologues 23 Na 35 Cl, 23 Na 37 Cl, 39 K 35 Cl, 39 K 37 Cl, 41 K 35 Cl and 41 K 37 Cl are considered. Laboratory data were used to refine ab initio potential energy curves in order to compute accurate ro-vibrational energy levels. Einstein A coefficients are generated using newly determined ab initio dipole moment curves calculated using the CCSD(T) method. New Dunham Yij constants for KCl are generated by a re-analysis of a published Fourier transform infrared emission spectra. Partition functions plus full line lists of ro-vibration transitions are made available in an electronic form as supplementary data to this paper and at www.exomol.com.

Study of the electronic and rovibronic structure of the X 2Σ+, A 2Π, and B 2Σ+ states of AlO

Abstract: The electronic structure of the X (2)Σ(+), A (2)Π, and B (2)Σ(+) states of aluminum monoxide (AlO) are studied via ab initio multi-reference configuration interaction calculations. Core correlation corrections, several basis sets, and active space choices are considered. Angular momentum and spin-orbit coupling terms are obtained at different levels of theory. The resulting ab initio curves are used to solve the associated rovibronic problem for the total angular momentum J up to 112.5 and then also refined by fitting to the experimental wavenumbers available in the literature, reproducing them with the root-mean-square error of 0.07 cm(-1). Theoretical rovibronic energy levels of AlO in its X (2)Σ(+), A (2)Π, and B (2)Σ(+) electronic states are presented including those from the X - B blue-green system.

Exomol molecular line lists - VI. A high temperature line list for phosphorus nitride

Abstract: Accuraterotational–vibrationallinelistsfor 31 P 14 Nand 31 P 15 Nintheirgroundelectronicstates 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 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 0–51 000 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 temperatures up to, at least, 5000 K. These new line lists are used to simulate spectra for phosphorus nitride at a range of temperatures and are deposited in the Strasbourg data centre. This work is performed as part of the ExoMol project.

Electron-impact resonant vibrational excitation and dissociation processes involving vibrationally excited N2 molecules

Abstract: Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron-N$_2$ collisions occurring through the N$_2^-(\textrm{X}\ ^2\Pi_g)$ resonant state are reviewed. New calculations are performed using accurate potential energies curves for the N$_2$ electronic ground state, taken from literature, and for the N$_2^-$ resonant state, obtained from $R$-matrix calculations. The calculations are extended also to the resonant excitation processes involving the N$_2$ ground state vibrational continuum, leading to dissociation. Electron impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided. The behavior of the dissociative cross sections is investigated for rotationally excited N$_2$ molecules, with $J=50,100$ and 150 and for different vibrational levels.

Dissociative recombination of N-2(+) : An ab initio study

Abstract: Cross sections for the dissociative recombination of ${\mathrm{N}}_{2}^{+}$ for ${v}_{i}^{+}=0--3$ are computed using multichannel quantum defect theory with molecular data generated using the $R$-matrix method. The calculation is completely ab initio and includes three electronic cores of the ion. Extensive comparisons are made with previous experimental and theoretical studies. Our cross section is in excellent agreement with experimental results and other theoretical results. Cross sections and isotropic rate coefficients are provided for all computed vibrational levels.

R-matrix calculations of low-energy electron collisions with methane

Abstract: R-matrix calculations are performed for electron collision with CH4 at energies between 0.02 and 15 eV using a series of different ab initio models for both the target and the full scattering system. A target model similar to the standard multi-reference configuration interaction used in electronic structure calculations is found to give the best results. Results are presented for elastic scattering, with particular emphasis on the Ramsauer–Townsend miminum, and for rotational excitation, momentum transfer and electron impact dissociation. Extensive comparisons are made with previous studies.

Rotational spectrum of SO3 and theoretical evidence for the formation of sixfold rotational energy-level clusters in its vibrational ground state.

Abstract: The structure of the purely rotational spectrum of sulphur trioxide 32S16O3 is investigated using a new synthetic line list. The list combines line positions from an empirical model with line intensities determined, in the form of Einstein coefficients, from variationally computed ro-vibrational wavefunctions in conjunction with an ab initio dipole moment surface. The empirical model providing the line positions involves an effective, Watsonian-type rotational Hamiltonian with literature parameter values resulting from least-squares fittings to observed transition frequencies. The formation of so-called 6-fold rotational energy clusters at high rotational excitation are investigated. The SO3 molecule is planar at equilibrium and exhibits a unique type of rotational-energy clustering associated with unusual stabilization axes perpendicular to the S–O bonds. This behaviour is characterized theoretically in the J range from 100–250. The wavefunctions for these cluster states are analysed, and the results are compared to those of a classical analysis in terms of the rotational-energy-surface formalism.

Rotational transitions induced by collisions of HD + ions with low-energy electrons

Abstract: A series of computations based on multichannel quantum defect theory have been performed in order to produce the cross sections of rotational transitions (excitations ${N}_{i}^{+}\ensuremath{-}2\ensuremath{\rightarrow}$ ${N}_{i}^{+}$, deexcitations ${N}_{i}^{+}$ $\ensuremath{\rightarrow}$ ${N}_{i}^{+}\ensuremath{-}2$, with ${N}_{i}^{+}=2$ to 10) and of their competitive process, the dissociative recombination, induced by collisions of ${\mathrm{HD}}^{+}$ ions with electrons in the energy range ${10}^{\ensuremath{-}5}$ to 0.3 eV. Maxwell anisotropic rate coefficients, obtained from these cross sections in the conditions of the Heidelberg Test Storage Ring (TSR) experiments $({k}_{B}{T}_{t}=2.8$ meV and ${k}_{B}{T}_{l}=45$ $\ensuremath{\mu}$eV), have been reported for those processes in the same electronic energy range. Maxwell isotropic rate coefficients have been presented as well for electronic temperatures up to a few hundred Kelvins. Very good overall agreement is found between our results for rotational transitions and the former theoretical computations as well as with experiment. Furthermore, due to the full rotational computations performed, the accuracy of the resulting dissociative recombination cross sections is improved considerably.

An R-matrix study of singlet and triplet continuum states of N2

Abstract: A systematic calculation of the positions and widths of the resonances converging on the first two excited states of N (A and B ) is presented. A closely-spaced grid of geometries is used to give continuous resonance curves without the need for curve fitting. Three methods, fitting the eigenphase sum, the time-delay method and the R-matrix specific QB method, are tested. Fits to the longest three time-delays are found to give the most reliable and complete determination of the resonance parameters. The low excitation energies of the A and B ion states results in complex resonance features with many avoided crossings leading to pronounced structures in both the resonance curves and the associated widths. The resonance curves likely to be important for dissociative recombination are identified. Their positions generally agree well with the calculations of Guberman, although in some cases their widths are narrower. Full data on all curves is provided.

QED correction for H-3(+)

Abstract: A quantum electrodynamics (QED) correction surface for the simplest polyatomic and polyelectronic system H3+ is computed using an approximate procedure. This surface is used to calculate the shifts to vibration-rotation energy levels due to QED; such shifts have a magnitude of up to 0.25 cm−1 for vibrational levels up to 15 000 cm−1 and are expected to have an accuracy of about 0.02 cm−1. Combining our H3+ QED correction surface with existing highly accurate Born-Oppenheimer, relativistic, and adiabatic components suggests that deviations of the resulting ab initio energy levels from observed ones are largely due to nonadiabatic effects.

Communication: Visible line intensities of the triatomic hydrogen ion from experiment and theory

Abstract: The visible spectrum of H3+ is studied using high-sensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak ro-vibrational transitions from the lowest rotational states of H3+ up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein B coefficients. Ab initio predictions for the Einstein B coefficients are obtained from a highly precise dipole moment surface of H3+ and found to be in excellent agreement, even in the region where states have been classified as chaotic.

Hybrid variation-perturbation method for calculating rovibrational energy levels of polyatomic molecules

Abstract: A procedure for calculation of rotation-vibration states of medium sized molecules is presented. It combines the advantages of variational calculations and perturbation theory. The vibrational problem is solved by diagonalizing a Hamiltonian matrix, which is partitioned into two sub-blocks. The first, smaller sub-block includes matrix elements with the largest contribution to the energy levels targeted in the calculations. The second, larger sub-block comprises those basis states which have little effect on these energy levels. Numerical perturbation theory, implemented as a Jacobi rotation, is used to compute the contributions from the matrix elements of the second sub-block. Only the first sub-block needs to be stored in memory and diagonalized. Calculations of the vibrational-rotational energy levels also employ a partitioning of the Hamiltonian matrix into sub-blocks, each of which corresponds either to a single vibrational state or a set of resonating vibrational states, with all associated rotational levels. Physically, this partitioning is efficient when the Coriolis coupling between different vibrational states is small. Numerical perturbation theory is used to include the cross-contributions from different vibrational states. Separate individual sub-blocks are then diagonalized, replacing the diagonalization of a large Hamiltonian matrix with a number of small matrix diagonalizations. Numerical examples show that the proposed hybrid variational-perturbation method greatly speeds up the variational procedure without significant loss of precision for both vibrational-rotational energy levels and transition intensities. The hybrid scheme can be used for accurate nuclear motion calculations on molecules with up to 15 atoms on currently available computers.

Molecular physics of elementary processes relevant to hypersonics: Electron-molecule collisions

Abstract: Non-resonant, electron-impact, vibro-electronic excitation cross sections, involving vibrationally excited N2 molecules, to the mixed valence-Rydberg b,c,o Πu and ′ b , ′ c , ′ e Σu + singlet states are presented. These cross sections are calculated using the so-called similarity approach, accounting for the vibronic coupling among excited states, and compared with the experiments and different theoretical calculations. New cross sections for the electron-impact resonant vibrational excitation of CO2 molecule are calculated, for the symmetric stretching mode, as a function of the incident electron energy and for the transitions (υi ,0,0)→ (υ f ,0,0) with υi = 0,1,2 and for some selected value of υ f in the interval υi ≤υ f ≤10. A resonance potential curve and associated widths are calculated using the R-matrix method. Rate coefficients, calculated by assuming a Maxwellian electron energy distribution function, are also presented for the same (υi ,0,0)→ (υ f ,0,0) transitions. Electron-impact cross sections and rate coefficients for resonant vibrational excitations involving the diatomic species N2, NO, CO, O2 and H2, for multi-quantic and mono-quantic transitions, are reviewed along with the cross sections and rates for the process of the dissociative electron attachment to H2 molecule, involving a Rydberg excited resonant state of the ion.

Low-energy electron collisions with the alanine molecule

Abstract: A theoretical study on elastic electron collisions with two conformers of amino acid alanine (CH3CH(NH2)COOH) is reported. Differential and integral cross sections are computed for collision energies in the 1–10 eV range. The UK molecular R-matrix codes are used to compute scattering amplitudes within the static exchange plus polarization (SEP) approximation. Both alanine conformers have large permanent dipole moment so to calculate cross sections the Born closure procedure is included to take into account long-range interactions. Comparisons of calculated differential cross sections with available data for glycine are made and display certain similarities. Two shape resonances are detected for each conformer: a narrow one located at 2.7 eV and 3.5 eV which is probably associated with the unoccupied π ∗ orbital of the carboxyl group, and a broader resonance at 8.6 eV and 9.8 eV.

A hybrid variational-perturbation calculation of the ro-vibrational spectrum of nitric acid

Abstract: Rotation-vibration spectra of the nitric acid molecule, HNO\3, are calculated for wavenumbers up to 7000~\cm. Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates solved using a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated {\it ab initio} at the CCSD(T)/aug-cc-pVQZ level of theory. Parameters of the PES and DMF are varied to minimize differences between the calculated and experimental transition frequencies and intensities. The average, absolute deviation between calculated and experimental values is 0.2~\cm\ for frequencies in the fundamental bands and 0.4~\cm\ for those in the first overtone and lowest combination bands. For the intensities, the calculated and experimental values differ by 0.3\% and 40\% for the fundamentals and overtones, respectively. The optimized PES and DMF are used to calculate the room-temperature ro-vibrational spectrum. These calculation reproduce both the form of the absorption bands, and fine details of the observed spectra, including the rotational structure of the vibrational bands and the numerous hot absorption band. Many of these hot bands are found to be missing from the compilation in HITRAN. A room temperature line list comprising $2 \times 10^{9}$ lines is computed.

Rotational Spectrum of SO_3 and Theoretical Evidence for the Formation of Rotational Energy Level Clusters in its Vibrational Ground State

Abstract: DANIEL S UNDERWOOD, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom; SERGEI N. YURCHENKO, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom; JONATHAN TENNYSON, Department of Physics and Astronomy, University College London, London, IX, United Kingdom; PER JENSEN, Faculty of Mathematics and Natural Sciences, University of Wuppertal, Wuppertal, Germany.

Rate Coefficients for Dissociative Attachment and Resonant Electron-impact Dissociation Involving Vibrationally Excited O 2 Molecules

Abstract: Rate coefficients for dissociative electron attachment and electron-impact dissociation processes, involving vibrationally excited molecular oxygen, are presented. Analytical fits of the calculated numerical data, useful in the applications, are also provided.

Recommended Isolated-Line Profile for Representing High-Resolution Spectroscoscopic Transitions

Abstract: transitions Jonathan Tennyson1, Peter F. Bernath2, Alain Campargue3, Attila G. Csaszar4, Ludovic Daumont,5 Robert R. Gamache6, Joseph T. Hodges7, Daniel Lisak8, Olga V. Naumenko9, Laurence S. Rothman10, Ha Tran11, Jean-Michel Hartmann11, Nikolai F. Zobov12, Jeanna Buldyreva13, Chris D. Boone14, Maria D. De Vizia15, Livio Gianfrani15, Robert McPheat16, Damien Weidmann16, Jonathan Murray17, Ngoc Hoa Ngo18, Oleg L. Polyansky1,12 1Department of Physics and Astronomy, University College London, UK; 2Department of Chemistry and Biochemistry,Old Dominion University, USA; 3Universite Grenoble 1/CNRS, France; 4Institute of Chemistry, Lorand Eotvos University, Hungary; 5GSMA, UMR CNRS 7331, Universite de Reims Champagne Ardenne, France; 6Department of Environmental, Earth, and Atmospheric Sciences University of Massachusetts Lowell, USA; 7National Institute of Standards and Technology, Gaithersburg, U.S.A.; 8Institute of Physics, Nicolaus Copernicus University, Torun, Poland; 9Institute of Atmospheric Optics, Russian Academy of Sciences, Tomsk, Russia; 10Harvard-Smithsonian Center for Astrophysics, Cambridge, U.S.A.; 11Laboratoire Interuniversitaire des Systemes Atmospheriques, UMR CNRS 7583, Universite Paris Est Creteil, France; 12Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; 13Institut UTINAM UMR CNRS 6213, Universite de Franche-Comte, Besancon, France; 14Department of Chemistry, University of Waterloo, Canada; 15Department of Mathematics and Physics, Second University of Naples, Caserta, Italy; 16Rutherford Appleton Laboratory, Didcot, UK; 17Space and Atmospheric Physics, Imperial College London, London, UK; 18Faculty of Physics, Hanoi National University of Education, Vietnam