The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
Jonathan Tennyson - One of the best experts on this subject based on the ideXlab platform.
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electron impact Rotational Excitation of the carbon monosulphide cs molecule
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Hemal N Varambhia, Alexandre Faure, Karola Graupner, Thomas A Field, Jonathan TennysonAbstract:Rotational Excitation of the carbon monosulphide (CS) molecule by thermal electron-impact is studied using the molecular R-matrix method combined with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are obtained for electron temperatures in the range 5-5000 K and for transitions involving levels up to J = 40. It is confirmed that dipole allowed transitions (Delta J = 1) are dominant and that the corresponding rate coefficients exceed those for Excitation by neutrals by at least five orders of magnitude. As a result, the present rates should be included in any detailed population model of CS in sources where the electron fraction is larger than similar to 10(-5), in particular in diffuse molecular clouds and interstellar shocks.
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Rotational Excitation of interstellar molecular ions by electrons
Journal of Physics: Conference Series, 2009Co-Authors: Alexandre Faure, Jonathan Tennyson, V. Kokoouline, Chris H. GreeneAbstract: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.
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Near-threshold Rotational Excitation of molecular ions by electron impact
J PHYS B-AT MOL OPT, 2006Co-Authors: Jonathan TennysonAbstract:New cross sections for the Rotational Excitation of H-3(+) by electrons are calculated ab initio at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with R-matrix wavefunctions, is assessed by comparison with rovibrational quantum defect theory calculations based on the treatment of Kokoouline and Greene (2003 Phys. Rev. A68 012703). Pure ANR Excitation cross sections are shown to be accurate down to threshold, except in the presence of large oscillating Rydberg resonances. These resonances occur for transitions with Delta J = 1 and are caused by closed-channel effects. A simple analytic formula is derived for averaging the Rotational probabilities over such resonances in a 3-channel problem. In accord with the Wigner law for an attractive Coulomb field, Rotational Excitation cross sections are shown to be large and finite at threshold, with a significant but moderate contribution from closed-channels.
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Near threshold Rotational Excitation of molecular ions by electron-impact
Journal of Physics B: Atomic Molecular and Optical Physics, 2006Co-Authors: Alexandre Faure, V. Kokoouline, Chris H. Greene, Jonathan TennysonAbstract:New cross sections for the Rotational Excitation of H+3 by electrons are calculated ab initio at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with R-matrix wavefunctions, is assessed by comparison with rovibrational quantum defect theory calculations based on the treatment of Kokoouline and Greene (2003 Phys. Rev. A 68 012703). Pure ANR Excitation cross sections are shown to be accurate down to threshold, except in the presence of large oscillating Rydberg resonances. These resonances occur for transitions with ΔJ = 1 and are caused by closed-channel effects. A simple analytic formula is derived for averaging the Rotational probabilities over such resonances in a 3-channel problem. In accord with the Wigner law for an attractive Coulomb field, Rotational Excitation cross sections are shown to be large and finite at threshold, with a significant but moderate contribution from closed-channels.
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electron impact Rotational Excitation of water
Monthly Notices of the Royal Astronomical Society, 2004Co-Authors: Alexandre Faure, J D Gorfinkiel, Jonathan TennysonAbstract:Rotational Excitation of H2O, HDO and D2O by thermal electron impact is studied using the molecular R-matrix method. Rate coefficients are obtained up to electron temperatures of 8000 K. De-Excitation rates and critical electron densities are also given. It is shown that the dominant transitions are those for which DeltaJ = 0, +/-1, as predicted by the dipolar Born approximation. However, a pure Born treatment is found to overestimate the cross-sections close to threshold energies and to neglect important (dipole forbidden) transitions, owing to the importance of short-range and threshold effects. In the context of cometary water, the contribution of electron collisions might explain the need for large H2O-H2O collisional Excitation rates in population models that neglect electrons.
Alexandre Faure - One of the best experts on this subject based on the ideXlab platform.
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Rotational Excitation of the interstellar nh2 radical by h2
Journal of Chemical Physics, 2017Co-Authors: N Bouhafs, Alexandre Faure, Francois Lique, A Bacmann, Hua GuoAbstract:We present quantum close-coupling calculations for the Rotational Excitation of the interstellar amidogen radical NH2 due to collisions with H2 molecules. The calculations are based on a recent, high-accuracy full-dimensional NH4 potential energy surface adapted for rigid-rotor scattering calculations. The collisional cross section calculations are performed for all transitions among the first 15 energy levels of both ortho- and para-NH2 and for total energies up to 1500 cm−1. Both para- and ortho-H2 colliding partners are considered. The cross sections for collision with para- and ortho-H2 are found to differ significantly, the magnitude of the ortho-H2 ones being dominant. No strong propensity rules are observed but transitions with Δkc=0 are slightly favored.
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electron impact Rotational Excitation of the carbon monosulphide cs molecule
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Hemal N Varambhia, Alexandre Faure, Karola Graupner, Thomas A Field, Jonathan TennysonAbstract:Rotational Excitation of the carbon monosulphide (CS) molecule by thermal electron-impact is studied using the molecular R-matrix method combined with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are obtained for electron temperatures in the range 5-5000 K and for transitions involving levels up to J = 40. It is confirmed that dipole allowed transitions (Delta J = 1) are dominant and that the corresponding rate coefficients exceed those for Excitation by neutrals by at least five orders of magnitude. As a result, the present rates should be included in any detailed population model of CS in sources where the electron fraction is larger than similar to 10(-5), in particular in diffuse molecular clouds and interstellar shocks.
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Rotational Excitation of interstellar molecular ions by electrons
Journal of Physics: Conference Series, 2009Co-Authors: Alexandre Faure, Jonathan Tennyson, V. Kokoouline, Chris H. GreeneAbstract: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.
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Rotational Excitation of HC_3N by H_2 and He at low temperatures
2006Co-Authors: Michael Wernli, Alexandre Faure, Laurent Wiesenfeld, Pierre ValironAbstract:Rates for Rotational Excitation of HC3N by collisions with He atoms and H2 molecules are computed for kinetic temperatures in the range 5-20K and 5-100K, respectively. These rates are obtained from extensive quantum and quasi-classical calculations using new accurate potential energy surfaces (PES).
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Near threshold Rotational Excitation of molecular ions by electron-impact
Journal of Physics B: Atomic Molecular and Optical Physics, 2006Co-Authors: Alexandre Faure, V. Kokoouline, Chris H. Greene, Jonathan TennysonAbstract:New cross sections for the Rotational Excitation of H+3 by electrons are calculated ab initio at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with R-matrix wavefunctions, is assessed by comparison with rovibrational quantum defect theory calculations based on the treatment of Kokoouline and Greene (2003 Phys. Rev. A 68 012703). Pure ANR Excitation cross sections are shown to be accurate down to threshold, except in the presence of large oscillating Rydberg resonances. These resonances occur for transitions with ΔJ = 1 and are caused by closed-channel effects. A simple analytic formula is derived for averaging the Rotational probabilities over such resonances in a 3-channel problem. In accord with the Wigner law for an attractive Coulomb field, Rotational Excitation cross sections are shown to be large and finite at threshold, with a significant but moderate contribution from closed-channels.
Vinod Prasad - One of the best experts on this subject based on the ideXlab platform.
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pulse train induced Rotational Excitation and orientation of a polar molecule
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014Co-Authors: Ashish Tyagi, Urvashi Arya, Bhavna Vidhani, Vinod PrasadAbstract:We investigate theoretically the Rotational Excitation and field free molecular orientation of polar HBr molecule, interacting with train of ultrashort laser pulses. By adjusting the number of pulses, pulse period and the intensity of the pulse, one can suppress a population while simultaneously enhancing the desired population in particular Rotational state. We have used train of laser pulses of different shaped pulse envelopes. The dynamics and orientation of molecules in the presence of pulse train of different shapes is studied and explained.
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Pulse shape effect of delayed pulse on non-adiabatic Rotational Excitation.
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2012Co-Authors: Urvashi Arya, Brijender Dahiya, Vinod PrasadAbstract:We examine the time evolution of Non-adiabatic Excitation of polar molecule in static field exposed to a combination of delayed pulses. The delayed pulse pair consists of half cycle pulse (HCP) and an another delayed pulse (either ultrashort half cycle pulse or zero area pulse). We describe how Non-adiabatic Rotational Excitation (NAREX) due to Gaussian HCP pulse alone can be greatly modified by applying ultrashort HCP/zero area pulse. It is also shown that non-adiabatic Rotational Excitation can be controlled by various laser parameters, out of which pulse shape plays the most significant role for controlling the dynamics. Time dependent Schrodinger equation (TDSE) of NAREX dynamics, are studied using efficient fourth order Runge Kutta method.
A Dalgarno - One of the best experts on this subject based on the ideXlab platform.
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Elastic scattering and Rotational Excitation of nitrogen molecules by sodium atoms
Journal of Chemical Physics, 2011Co-Authors: Jérôme Loreau, Peng Zhang, A DalgarnoAbstract:A quantal study of the Rotational Excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN2 complex, with the N2 molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple Excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N2. The total, differential, and momentum transfer cross sections for Rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm−1 and 1500 cm−1. The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na–N2 collisions occur in the mesosphere.A quantal study of the Rotational Excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN2 complex, with the N2 molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple Excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N2. The total, differential, and momentum transfer cross sections for Rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm−1 and 1500 cm−1. The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na–N2 collisions occur in the mesosphere.
Chris H. Greene - One of the best experts on this subject based on the ideXlab platform.
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Rotational Excitation of interstellar molecular ions by electrons
Journal of Physics: Conference Series, 2009Co-Authors: Alexandre Faure, Jonathan Tennyson, V. Kokoouline, Chris H. GreeneAbstract: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.
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Near threshold Rotational Excitation of molecular ions by electron-impact
Journal of Physics B: Atomic Molecular and Optical Physics, 2006Co-Authors: Alexandre Faure, V. Kokoouline, Chris H. Greene, Jonathan TennysonAbstract:New cross sections for the Rotational Excitation of H+3 by electrons are calculated ab initio at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with R-matrix wavefunctions, is assessed by comparison with rovibrational quantum defect theory calculations based on the treatment of Kokoouline and Greene (2003 Phys. Rev. A 68 012703). Pure ANR Excitation cross sections are shown to be accurate down to threshold, except in the presence of large oscillating Rydberg resonances. These resonances occur for transitions with ΔJ = 1 and are caused by closed-channel effects. A simple analytic formula is derived for averaging the Rotational probabilities over such resonances in a 3-channel problem. In accord with the Wigner law for an attractive Coulomb field, Rotational Excitation cross sections are shown to be large and finite at threshold, with a significant but moderate contribution from closed-channels.