Showing papers by "Jonathan Tennyson published in 2000"

Accurate partition function and thermodynamic data for water

Abstract: The partition function, Q, of H216O is calculated by explicit summation of about 10 500 experimental vibration-rotation energy levels and very high accuracy estimates are obtained for the specific heat capacity (Cp), the Gibbs enthalpy function (gef), the Helmholtz function (hcf) and the entropy (S) of gas phase water as a function of temperature. For temperatures above 600 K it is necessary to augment the sum with theoretical estimates of the energy levels. These are obtained from high accuracy variational calculations which are extended to dissociation using a model for rotational levels based on a Pade approximant. Estimates for the partition function and other thermodynamic quantities are obtained for temperatures up to 6000 K and temperature dependent error bars presented. All estimates are highly accurate with the exception of Cp for T>5000 K, for which further work is required.

The role of H + 3 in planetary atmospheres

Abstract: Spectroscopic studies of the upper atmospheres of the giant planets using infrared wavelengths sensitive to the H3+ molecular ion show that this species plays a critical role in determining the phy...

Dissociative recombination of NO+: calculations and comparison with experiment

Abstract: Multichannel quantum defect calculations for NO + dissociative recombination (DR) for electron energies from threshold to 8 eV are presented. The calculations use electronic energies and autoionization widths of valence states obtained from ab initio R-matrix calculations with the corresponding potential curves calibrated using available spectroscopic data. Six valence states open to dissociation are included in the final calculations. Excellent agreement with the measured cross sections is obtained for the low-energy DR, up to 3 eV and, for the first time, the peak observed in the cross section at high energy is accounted for. The importance of the various dissociative states at different electron energies, as well as the direct and indirect processes, is discussed. Compared to previous theoretical studies, the inclusion of a third dissociative state of 2 � symmetry and the larger autoionization width of the B� 2� state are found to be particularly important for the agreement with experiment. (Some figures in this article are in colour only in the electronic version; see www.iop.org)

New studies of the visible and near-infrared absorption by water vapour and some problems with the HITRAN database

Abstract: New laboratory measurements and theoretical calculations of integrated line intensities for water vapour bands in the near-infrared and visible (8500–15800 cm−1) are summarised. Band intensities derived from the new measured data show a systematic 6 to 26% increase compared to calculations using the HITRAN-96 database. The recent corrections to the HITRAN database [Giver et al., J. Quant. Spectrosc. Radiat. Transfer, 66, 101–105, 2000] do not remove these discrepancies and the differences change to 6 to 38%. The new data is expected to substantially increase the calculated absorption of solar energy due to water vapour in climate models based on the HITRAN database.

An accurate, global, ab initio potential energy surface for the H+ 3 molecule

Abstract: A new global, ground-state, Born-Oppenheimer surface is presented for the H+ 3 system. The energy switching approach has been used to combine different functional forms for three different regimes:...

The near ultraviolet rotation-vibration spectrum of water

Abstract: A new ab initio linelist of water vibration-rotation transitions extending up to 26 000 cm−1 is presented. This linelist is used to analyze the near-ultraviolet portion of the long pathlength water absorption spectrum of Carleer et al. [J. Chem. Phys. 111, 2444 (1999)]. A total of 299 of the 568 observed transitions between 21 400 and 25 232 cm−1 are assigned. These transitions belong to eight excited vibrational states: (4,2)−1, (7,0)+0, (7,0)−0, (6,0)+2, (6,0)−2, (7,0)−1, (8,0)−0, and (8,0)−0, in local mode notation. Only three of these states have been observed previously. Observed and calculated energy levels are presented for these vibrational states and the band origins are determined.

Electron collisions with ClO using the R-matrix method

Abstract: The R-matrix method is used to calculate elastic and the excitation cross sections of the six lowest lying electronically excited states of the ClO molecule. These states, of symmetry 1 4Σ-, A 2Π, 1 2Σ-, 1 2Δ, 2 4Σ- and 1 2Σ+, have vertical excitation energies in the range 3.48 to 6.99 eV. Except for the state A 2Π, all other excited states are dissociative. We find a bound state of ClO- with 1Σ+ symmetry with an adiabatic electron affinity of 1.128 eV at an equilibrium bond length of 3.25 a0. There are shape resonances of 1Π and 3Π symmetries at 1.6 and 2.9 eV respectively. Rotationally summed cross sections are obtained for elastic and electronically inelastic scattering for electron-impact energies up to 10 eV.

Using laboratory spectroscopy to identify lines in the k- and l -band spectrum of water in a sunspot

Abstract: The infrared spectrum of a sunspot is analyzed in the L-band region 3.1-4.0 μm (2497-3195 cm-1) and 2.02-2.35 μm (4251-4962 cm-1) in the K band. A new laboratory emission spectrum covering 2500- 6000 cm-1 is analyzed to help make the assignments. Quantum number assignments are made using linelists computed using variational calculations, assisted by tabulations of experimental energy levels. There are 1207 new H216O lines assigned in the L band and 508 new lines in the K band. Vibrational band origins of 11242.8 ± 0.1 cm-1 and 12586 ± 1 cm-1 are obtained for the (051) and (061) states.

Relative equilibria of D2H+ and H2D+

Abstract: Relative equilibria of molecules are classical trajectories corresponding to steady rotations about stationary axes during which the shape of the molecule does not change. They can be used to explain and predict features of quantum spectra at high values of the total angular momentum J in much the same way that absolute equilibria are used at low J. This paper gives a classification of the symmetry types of relative equilibria of AB(2) molecules and computes the relative equilibria bifurcation diagrams and normal mode frequencies for D2H+ and H2D+. These are then fed into a harmonic quantization procedure to produce a number of predictions concerning the structures of energy level clusters and their rearrangements as J increases. In particular the formation of doublet pairs is predicted for H2D+ from J approximate to 26.

H-3(+) near dissociation: theoretical progress

Abstract: The observation of an infrared spectrum of the H 3 + molecular ion at its dissociation limit by Carrington and co–workers has presented a tremendous challenge to theory. To compute this spectrum it is necessary to model accurately the global potential energy surface of H 3 + , vibrationally excited states at dissociation, rotational excitation, lifetimes of rotationally excited ‘shape’ resonances, and infrared transition dipoles near dissociation. Progress in each of these aspects is reviewed and results are presented for highly excited vibrational levels using a new ab initio global potential. The use of massively parallel computers in solving aspects of the problem is discussed.

Relative equilibria of D(2)H(+) and H(2)D(+)

Abstract: Relative equilibria of molecules are classical trajectories corresponding to steady rotations about stationary axes during which the shape of the molecule does not change. They can be used to explain and predict features of quantum spectra at high values of the total angular momentumJ in much the same way that absolute equilibria are used at low J. This paper gives a classi® cation of the symmetry types of relative equilibria of AB2 molecules and computes the relative equilibria bifurcation diagrams and normal mode frequencies for D2H ‡ and H2D ‡ . These are then fed into a harmonic quantization procedure to produce a number of predictions concerning the structures of energy level clusters and their rearrangements as J increases. In particular the formation of doublet pairs is predicted for H2D ‡ from J o 26.

Measurement of Water Absorption Cross-Sections for the Exploitation of GOME Data - Executive Summary of Final Report

Abstract: Report associated with the Measurement of H2O Absorption Cross-Sections funded by the European Space Agency (ESA) dataset held at CEDA