Jonathan Tennyson

A high-accuracy computed water line list

A computed list of H2 16 O infrared transition frequencies and intensities is presented. The list, BT2, was produced using a discrete variable representation two-step approach for solving the rotation‐vibration nuclear motions. It is the most complete water line list in existence, comprising over 500 million transitions (65 per cent more than any other list) and it is also the most accurate (over 90 per cent of all known experimental energy levels are within 0.3 cm −1 of the BT2 values). Its accuracy has been confirmed by extensive testing against astronomical and laboratory data. The line list has been used to identify individual water lines in a variety of objects including comets, sunspots, a brown dwarf and the nova-like object V838 Mon. Comparison of the observed intensities with those generated by BT2 enables water abundances and temperatures to be derived for these objects. The line list can also be used to provide an opacity for models of the atmospheres of M dwarf stars and assign previously unknown water lines in laboratory

The ab initio calculation of the vibrational‐rotational spectrum of triatomic systems in the close‐coupling approach, with KCN and H2Ne as examples

A Hamiltonian for the vibration‐rotation motions of atom–diatom systems is derived in body‐fixed coordinates and a method for its solution as a close‐coupled secular problem is formulated. The radial coordinate is expanded in Morse oscillator functions. Calculations on KCN and H2Ne are presented. For KCN the neglect of Coriolis interactions is found to have little effect. Extensions of the method to problems in more dimensions are suggested.

Water vapour in the atmosphere of a transiting extrasolar planet

Water is predicted to be among the most abundant (if not the most abundant) molecular species after hydrogen in the atmospheres of close-in extrasolar giant planets (‘hot Jupiters’). Several attempts have been made to detect water on such planets, but have either failed to find compelling evidence for it or led to claims that should be taken with caution. Here we report an analysis of recent observations of the hot Jupiter HD 189733b (ref. 6) taken during the transit, when the planet passed in front of its parent star. We find that absorption by water vapour is the most likely cause of the wavelength-dependent variations in the effective radius of the planet at the infrared wavelengths 3.6 μm, 5.8 μm (both ref. 7) and 8 μm (ref. 8). The larger effective radius observed at visible wavelengths may arise from either stellar variability or the presence of clouds/hazes. We explain the report of a non-detection of water on HD 189733b (ref. 4) as being a consequence of the nearly isothermal vertical profile of the planet’s atmosphere.

A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA)

We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of zero-dimensional and one-dimensional interstellar sources.

Experimental Energy Levels of the Water Molecule

Experimentally derived energy levels are presented for 12 248 vibration–rotation states of the H2 16O isotopomer of water, more than doubling the number in previous, disparate, compilations. For each level an error and reference to source data is given. The levels have been checked using energy levels derived from sophisticated variational calculations. These levels span 107 vibrational states including members of all polyads up to and including 8v. Band origins, in some cases estimates, are presented for 101 vibrational modes.

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 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 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 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

The calculation of the vibration-rotation energies of triatomic molecules using scattering coordinates

Department of Physics and Astronomy, University College London, Gower Street, London WCIE 6BT, England Received 25 January 1986 This paper is a review of work I have been involved with concerning the calculation of ro-vibrational energy levels and wavefunctions, mainly of triatomic systems. The method reviewed is that of Tennyson and Sutcliffe for the calculation of spectra of triatomics as atom-diatom collision complexes, which is particularly ap- propriate for molecules with one or more large amplitude vibrational mode. The method uses polynomial basis functions to carry the nuclear motions and is variational for a given potential. Hamiltonians for four different sets of body-fixed axes are derived. The computational implementation of the method is discussed, including improvements to some published algorithms. The use of a two step (secondary) variational procedure for highly-excited rotational states is discussed and sample results given. Extensions to non-Born-Oppenheimer problems, transition intensities and polyatomic molecules are also considered. Comparisons are made with other techniques for calculating ro-vibrational spectra with some specific molecular examples.

DVR3D: a program suite for the calculation of rotation-vibration spectra of triatomic molecules

The DVR3D program suite calculates energy levels, wavefunctions, and where appropriate dipole transition moments, for rotating and vibrating triatomic molecules. Potential energy and, where necessary, dipole surfaces must be provided. Expectation values of geometrically defined functions can be calculated, a feature which is particularly useful for fitting potential energy surfaces. The programs use an exact (within the Born–Oppenheimer approximation) Hamiltonian and offer a choice of Jacobi or Radau internal coordinates and several body-fixed axes. Rotationally excited states are treated using an efficient two-step algorithm. The programs uses a Discrete Variable Representation (DVR) based on Gauss–Jacobi and Gauss–Laguerre quadrature for all 3 internal coordinates and thus yields a fully point-wise representation of the wavefunctions. The vibrational step uses successive diagonalisation and truncation which is implemented for a number of possible coordinate orderings. The rotational, expectation value and transition dipole programs exploit the savings offered by performing integrals on a DVR grid. The new version has been rewritten in FORTRAN 90 to exploit the dynamic array allocations and the algorithm for dipole and spectra calculations have been substantially improved. New modules allow the z-axis to be embedded perpendicular to the plane of the molecule and for the calculation of expectation values.

Spectroscopic properties of the H{sup +}{sub 3} molecule: A new calculated line list

A new list of H{sup +}{sub 3} infrared transition frequencies and intensities is presented. This list greatly extends the range of transitions considered to both higher energy and higher rotational states. The 3{times}10{sup 6} transitions are found to significantly affect both the absorption coefficient of H{sup +}{sub 3} and its cooling properties at temperatures above 1000 K. It is hoped these new data will be used for models of cool stars of low metallicity, the giant planets, and other warm bodies composed largely of H{sub 2}. {copyright} {ital 1996 The American Astronomical Society.}

Quantum dynamics of non-rigid systems comprising two polyatomic fragments

We combine earlier treatments for the embedding of body-fixed coordinates in linear molecules with the close-coupling formalism developed for atomdiatom scattering and derive a hamiltonian which is most convenient for describing the nuclear motions in van der Waals complexes and other non-rigid systems comprising two polyatomic fragments, A and B. This hamiltonian can still be partitioned in the form HA + HB + HINT , just as the space-fixed hamiltonian. The body-fixed form, however, has several advantages. We discuss solution strategies for the rovibrational problem in non-rigid dimers, based on this partitioning of the hamiltonian. Finally, in view of the size of the general polyatomic-polyatomic case, we suggest problems which should be currently practicable.