Showing papers by "Jonathan Tennyson published in 2009"

IUPAC critical evaluation of the rotational-vibrational spectra of water vapor. Part I—Energy levels and transition wavenumbers

Abstract: This is the first part of a series of articles reporting critically evaluated rotational– vibrational line positions, transition intensities, pressure dependence and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. The present article contains energy levels and data for line positions of the singly substituted isotopologues H2

IUPAC critical evaluation of the rotational–vibrational spectra of water vapor. Part I—Energy levels and transition wavenumbers for H217O and H218O

Abstract: This is the first part of a series of articles reporting critically evaluated rotational–vibrational line positions, transition intensities, pressure dependence and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. The present article contains energy levels and data for line positions of the singly substituted isotopologues H217O and H218O. The procedure and code MARVEL, standing for measured active rotational–vibrational energy levels, is used extensively in all stages of determining the validated levels and lines and their self-consistent uncertainties. The spectral regions covered for both isotopologues H217O and H218O are 0 – 17 125 cm - 1 . The energy levels are checked against ones determined from accurate variational calculations. The number of critically evaluated and recommended levels and lines are, respectively, 2687 and 8614 for H217O, and 4839 and 29 364 for H218O. The extensive lists of MARVEL lines and levels obtained are deposited in the Supplementary Material, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved. A distinguishing feature of the present evaluation of water spectroscopic data is the systematic use of all available experimental data and validation by first-principles theoretical calculations.

A variationally computed T = 300 K line list for NH3.

Abstract: Calculations are reported on the rotation-vibration energy levels of ammonia with associated transition intensities. A potential energy surface obtained from coupled cluster CCSD(T) calculations and subsequent fitting against experimental data is further refined by a slight adjustment of the equilibrium geometry, which leads to a significant improvement in the rotational energy level structure. A new accurate ab initio dipole moment surface is determined at the frozen core CCSD(T)/aug-cc-pVQZ level. The calculation of an extensive ammonia line list necessitates a number of algorithmic improvements in the program TROVE that is used for the variational treatment of nuclear motion. Rotation-vibration transitions for (NH3)-N-14 involving states with energies up to 12000 cm(-1) and rotational quantum number J = 20 are calculated. This gives 3.25 million transitions between 184400 energy levels. Comparisons show good agreement with data in the HITRAN database but suggest that HITRAN is missing significant ammonia absorptions, particularly in the near-infrared.

Water in HD 209458b's atmosphere from 3.6 - 8 microns IRAC photometric observations in primary transit

Abstract: The hot Jupiter HD 209458b was observed during primary transit at 36, 45, 58 and 80 microns using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope We detail here the procedures we adopted to correct for the systematic trends present in the IRAC data The light curves were fitted including limb darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, finding almost identical results The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 36 microns, 1469 +- 0013 % and 1448 +- 0013 %; at 45 microns, 1478 +- 0017 % ; at 58 microns, 1549 +- 0015 % and at 80 microns 1535 +- 0011 % Our results clearly indicate the presence of water in the planetary atmosphere Our broad band photometric measurements with IRAC prevent us from determining the additional presence of other other molecules such as CO, CO2 and methane for which spectroscopy is needed While water vapour with a mixing ratio of 10^-4-10^-3 combined with thermal profiles retrieved from the day-side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile

R-matrix calculation of low-energy electron collisions with uracil.

Abstract: R-matrix calculations on electron-uracil collisions are presented within the static exchange, static exchange plus polarization, and close-coupling approximations. Particularly as input for the close-coupling calculations, a series of target calculations is performed which considers low-lying singlet and triplet excited states of the uracil target. The scattering calculations find three low-lying shape resonances of A2″ symmetry and three higher-energy Feshbach resonances of A2′ symmetry. In both symmetries the precise resonance parameters are found to be sensitive to the treatment of polarization effects employed. Cross sections are presented for both elastic scattering and electronic excitation. Comparisons are made with energy-dependent, differential cross section measurements at 90° angle and good agreement is found for scattering energies above 0.5 eV.

Electron and positron collisions with polar molecules: studies with the benchmark water molecule

Abstract: It is difficult to measure low-energy cross sections for collisions of charged particles with strongly dipolar systems since the magnitude of such cross sections is completely dominated by collisions in the forward direction. Theoretically, it is possible to account for the strong forward scattering using the Born approximation but the procedure for combining Born 'top-up' with the more sophisticated treatments required to treat the scattering in other directions is not unique. This comment describes recent progress in describing both electron and positron collisions with polar molecules taking the important water molecule as a benchmark. Previous calculations on electron water at collision energies below 7 eV are compared with new experiments. Positron water studies up to 10 eV are re-analysed based on given experimental acceptance profiles, which depend on the details of the apparatus and method used in the measurements. It is suggested that theory is capable of giving reliable results for elastic and rotationally inelastic electron/positron collisions with strongly dipolar species.

State-selective spectroscopy of water up to its first dissociation limit.

Abstract: A joint experimental and first-principles quantum chemical study of the vibration-rotation states of the water molecule up to its first dissociation limit is presented. Triple-resonance, quantum state-selective spectroscopy is used to probe the entire ladder of water’s stretching vibrations up to 19 quanta of OH stretch, the last stretching state below dissociation. A new ground state potential energy surface of water is calculated using a large basis set and an all-electron, multireference configuration interaction procedure, which is augmented by relativistic corrections and fitted to a flexible functional form appropriate for a dissociating system. Variational nuclear motion calculations on this surface are used to give vibrational assignments. A total of 44 new vibrational states and 366 rotation-vibration energy levels are characterized; these span the region from 35 508 to 41 126 cm−1 above the vibrational ground state.

Water in the near-infrared spectrum of comet 8P/Tuttle

Abstract: A B S T R A C T High-resolution spectra of comet 8P/Tuttle were obtained in the frequency range 3449.0– 3462.2 cm −1 on 2008 January 3 UT using CGS4 with echelle grating on United Kingdom Infrared Telescope. In addition to observing solar pumped fluorescent lines of H 2O, the long integration time (152 min on target) enabled eight weaker H 2O features to be assigned, most of which had not previously been identified in cometary spectra. These transitions, which are from higher energy upper states, are similar in character to the so-called SH lines recorded in the post Deep Impact spectrum of comet Tempel 1. We have identified certain characteristics that these lines have in common, and which in addition to helping to define this new class of cometary line give some clues to the physical processes involved in their production. Finally, we derive an H 2O rotational temperature of 62 ± 5 K and a water production rate of (1.4 ± 0.3) × 10 28 molecules s −1 .

Towards sympathetic cooling of large molecules: cold collisions between benzene and rare gas atoms

Abstract: This paper reports on calculations of collisional cross sections for the complexes X–C6H6 (X=3He, 4He, Ne) at temperatures in the range 1 μK–10 K and shows that relatively large cross sections in the 103–105 A2 range are available for collisional cooling. Both elastic and inelastic processes are considered in this temperature range. The calculations suggest that sympathetically cooling benzene to microkelvin temperatures is feasible using these co-trapped rare gas atoms in an optical trap.

Rotational cooling of HD+ molecular ions by superelastic collisions with electrons.

Abstract: Merging an HD+ beam with velocity matched electrons in a heavy ion storage ring we observed rapid cooling of the rotational excitations of the HD+ ions by superelastic collisions (SEC) with the electrons. The cooling process is well described using theoretical SEC rate coefficients obtained by combining the molecular R-matrix approach with the adiabatic nuclei rotation approximation. We verify the DeltaJ=-2 SEC rate coefficients, which are predicted to be dominant as opposed to the DeltaJ=-1 rates and to amount to (1-2)x10;{-6} cm;{3} s;{-1} for initial angular momentum states with J< or =7, to within 30%.

Electron collision with the silicon monoxide (SiO) molecule using the R-matrix method

Abstract: SiO is a molecule that is well known astrophysically. Electron scattering calculations are presented at the static-exchange and close-coupling approximations, one including 24 target states and another including 48 states. Our study predicts the existence of several low-lying narrow 2Π, 2Δ and 2Σ− Feshbach resonances and confirms the existence of a 2Π bound state. Results from the 48-state close-coupling calculation have been employed to calculate rotational (de)excitation rates and rate-fitting coefficients, which are useful in astrophysical modelling. Ionization cross sections, rotationally summed and resolved differential and integral cross sections are also presented.

Sympathetic cooling by collisions with ultracold rare gas atoms, and recent progress in optical Stark deceleration.

Abstract: We propose a general scheme for sympathetic cooling of molecules to µK temperatures on a timescale of seconds. Experimental parameters have been estimated from theory, which indicate the viability of the scheme. This method, which is particularly suited to optical Stark deceleration, utilises ultracold, laser cooled metastable rare gas atoms quenched to their ground state as collision partners to co-trapped molecular species within a deep optical trap (150 mK). We also describe the measurement of the role of laser-induced molecular alignment on the dipole force in optical Stark deceleration and outline progress towards the realisation of chirped optical Stark deceleration for producing slow molecular beams with mK energy spreads.

Electron re-scattering from aligned linear molecules using the R-matrix method

Abstract: Electron re-scattering in a strong laser field provides an important probe of molecular structure and processes. The laser field drives the ionization of the molecule, followed by acceleration and subsequent recollision of the electron with the parent molecular ion, the scattered electrons carry information about the nuclear geometry and electronic states of the molecular ion. It is advantageous in strong field experiments to work with aligned molecules, which introduces extra physics compared to the standard gas-phase, electron–molecule scattering problem. The formalism for scattering from oriented linear molecules is presented and applied to H2 and CO2. Differential cross sections are presented for (re-)scattering by these systems concentrating on the most common, linear alignment. In H2 these cross sections show significant angular structure which, particularly for a scattering angle of 90°, are predicted to vary significantly between re-collisions stimulated by an even or an odd number of photons. In CO2 these cross sections are zero indicating the necessity of using non-parallel alignment with this molecule.

Electron collisions with the NO 2 radical using the R -matrix method

Abstract: The $R$-matrix method is used to calculate the elastic integral, differential, momentum transfer cross sections, and the excitation cross sections from the ground state $X\text{ }{^{2}A}_{1}$ to the five low-lying electronically excited states $A\text{ }{^{2}B}_{1}$, $B\text{ }{^{2}B}_{2}$, $C\text{ }{^{2}A}_{2}$, ${^{4}A}_{2}$, and ${^{4}B}_{2}$ of the ${\text{NO}}_{2}$ radical. Twenty-one target states are included in the close-coupling expansion of the scattering system, where each target state is represented by configuration-interaction wave function. The calculations give two shape resonances of ${^{3}B}_{1}$ and ${^{1}B}_{1}$ symmetries located at 1.18 and 2.33 eV, respectively, with a common configuration $6{a}_{1}\text{ }2{b}_{1}$. We also detect eight core-excited shape resonances and one Feshbach resonance. Partial elastic, total, and electronic excitation cross sections are presented and compared with the limited previous work. The dissociative nature of the ${^{3}B}_{1}$ and ${^{1}B}_{1}$ shape resonances is explored by performing scattering calculations in which one N-O bond is stretched while the other bond and the bonding angle are frozen. These resonances support dissociative attachment yielding NO and ${\text{O}}^{\ensuremath{-}}$ in their respective ground states.

A modified potential for HO2 with spectroscopic accuracy

Abstract: Seven ground state potential energy surfaces for the hydroperoxyl radical are compared. The potentials were determined from either high-quality ab initio calculations, fits to spectroscopic data, or a combination of the two approaches. Vibration-rotation calculations are performed on each potential and the results compared with experiment. None of the available potentials is entirely satisfactory although the best spectroscopic results are obtained using the Morse oscillator rigid bender internal dynamics potential [Bunker et al., J. Mol. Spectrosc. 155, 44 (1992)]. We present modifications of the double many-body expansion IV potential of Pastrana et al. [J. Chem. Phys. 94, 8093 (1990)]. These new potentials reproduce the observed vibrational levels and observed vibrational levels and rotational constants, respectively, while preserving the good global properties of the original potential.

Rotational excitation of interstellar molecular ions by electrons

Abstract: Electrons are known to be efficient in rotationally exciting molecular ions in cold ionized media. Rotational effects have also been shown to affect the dissociative recombination (DR) process. Electron collisions are thus expected to play a significant role in the thermalization and dissociation dynamics of molecular ions, both in the laboratory and in space. Using the molecular R-matrix method combined with the Adiabatic-Nuclei-Rotation (ANR) approximation corrected for threshold and closed-channel effects, we have computed new rate coefficients for the rotational excitation of H+3 and HCO+ by electrons at temperatures from 10 to 1 000K. At temperatures above rotational thresholds, rotational rates are found to compete or even dominate those of dissociative recombination, suggesting that electron collisions provide a possible source of rotational (de)excitation in DR measurements.

R-matrix calculation of electron collisions with the BF+ molecular ion

Abstract: Electron collisions with the BF+ molecular ion are studied using the framework of the diatomic version of the UK molecular R-matrix codes. A configuration-interaction calculation is performed for BF+ to obtain potential energy curves and target properties for 14 lowest doublet and quartet states. Scattering calculations are performed which yield resonance parameters and excitation cross sections in the energy range 0–20 eV. Cross sections for rotational excitations and an approximate calculation for the electron impact dissociation cross section for BF+ are also presented.

Calculations of cross sections data for scattering of electrons on BF3

Abstract: Institute of Physics, Pregrevica 118, 11080 Belgrade, Serbia The R-matrix method provides a complete theoretical framework for the treatment of low energy electron collisions. The method has been implemented into code Quantemol-N (EE) with a goal to provide users in plasma modeling, swarm studies and other applications with an option to calculate the missing data. In this paper we report on cross sections and rate coefficients for hydrogen bromide obtained by using Quantemol-N. The total cross section has been calculated both with and without Born corrections.

Is there anybody out there

Abstract: The possibility of life elsewhere in the Universe has fascinated mankind since antiquity and quite possibly before. As this book recognises, we are now approaching an era where astronomers will have the techniques to investigate the fundamental issue of whether there is life outside our own solar system in a fully scientific fashion. What has taken the search for extraterrestrial life out of the realms of metaphysics and science fiction to the subject of legitimate scientific research and grant proposals is the discovery of many planets orbiting other stars. The first of these was only identified in the middle of the last decade; so far about 300 planetary systems have been identified, some of them containing multiple planets. The number of detected planets is increasing rapidly as new telescopes and new detection techniques come on stream. What is already clear is that planetary systems are ubiquitous and are found even in circumstances where they were not expected, meaning that astronomers have had to drastically revise their mechanisms for the formation of such systems. Indeed these changes have led Alan Boss to assert in a recent book [1] that most stars in our galaxy support earth-like planets suggesting that there are about 100 billion such planets in our galaxy alone. Furthermore, Boss asserts that most of these planets will be inhabited. However, knowing there are many planets out there, and even suspecting that they may be inhabited, is a lot different to actually having evidence-based knowledge that any of them are inhabited. The challenge of detecting life outside the solar system basically breaks down into three possible techniques: waiting for alien visitors, looking for alien signals, and trying to observe the evidence for alien life forms. Jones dismisses the evidence for alien visitation pretty much without considering it. His view is widely held by most scientists and it is difficult to see much beyond hysteria. As I write, it has been established that extensive damage to a wind turbine in the east of England and which was widely reported as being due to an Unidentified Flying Object (UFO), was much more prosaically caused by a bolt sheering. Such occurrences are common. There have been several sustained campaigns which have been designed to search for extraterrestrial intelligence generically known as SETI. These have been based on trying to detect signals from nearby stars (or presumably planets orbiting them). Thus, far all of these have been unsuccessful in their primary aim of detecting a clear, intelligent signal. However SET@home was a marvellous exercise in communitybased grid computing as individuals worldwide downloaded a screen saver which analysed the data recorded by the SETI experiment at the Arecibo radio Observatory in Puerto Rico using computer cycles when their personal computers would otherwise be idle. That the various SETI experiments have so far drawn a blank is something that I for one find unsurprising given that our presence on Earth would not be detectable by any of the experiments performed from the distance of a nearby star. So far, SETI experiments have, in addition to being sensitive only to intelligent civilisations actively broadcasting their presence, have also had to second-guess at what particular wavelength such a broadcast is being attempted. Of course there has been one astronomical detection of life. The American astronomer Carl Sagan persuaded NASA to turn the detectors aboard the Jupiter-bound Galileo spacecraft on Earth and look carefully at us for signs of life. The results are very insightful. Sagan and co-workers [2] found three different signatures of life. They could clearly detect activity at radio wavelengths associated with radio communications and hence intelligent life on Earth. They also observed a surface pigment with a sharp

Electron collisions with the NO2 radical using the R-matrix method

Abstract: The R-matrix method is used to calculate the elastic integral, differential, momentum transfer cross sections, and the excitation cross sections from the ground state X (2)A(1) to the five low-lying electronically excited states A B-2(1), B B-2(2), C (2)A(2), (4)A(2), and B-4(2) of the NO2 radical Twenty-one target states are included in the close-coupling expansion of the scattering system, where each target state is represented by configuration-interaction wave function The calculations give two shape resonances of B-3(1) and B-1(1) symmetries located at 118 and 233 eV, respectively, with a common configuration 6a(1) 2b(1) We also detect eight core-excited shape resonances and one Feshbach resonance Partial elastic, total, and electronic excitation cross sections are presented and compared with the limited previous work The dissociative nature of the B-3(1) and B-1(1) shape resonances is explored by performing scattering calculations in which one N-O bond is stretched while the other bond and the bonding angle are frozen These resonances support dissociative attachment yielding NO and O- in their respective ground states

Previously Unobserved Water Lines Detected in the Post-Impact Spectrum

Abstract: The recently puplished Barber-Tennyson (BT2) synthetic H$_2$O water line list is the most complete and accurate line list in existence. It is finding application in a wide range of astrophysical environments. UKIRT spectra of comet Tempel 1, obtained after the 'Deep Impact' event, revealed several known H$_2$O solar pumped fluorescent (SPF)lines in the 2.8945 to 2.8985 $\mu$m region. In addition, using synthetic spectra produced with BT2, several emission lines were identified that had not previously been recorded in cometary spectra. Unlike the SPF lines, which are transitions from doubly-excited stretch states, these transitions, that we label 'SH', are from states with three or four quanta of vibrational excitation. The SH features were particularly strong during the period 20-40 minutes after impact.