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Title: Vibrational relaxation and dissociative recombination of H{sub 2}{sup +} induced by slow electrons

Abstract

We present calculations of cross sections and rate coefficients for the dissociative recombination of H{sub 2}{sup +} ions initially in v=0-6 vibrational levels, together with rate coefficients for the competing electron-induced vibrational deexcitation. We used the multichannel quantum defect theory with a second-order treatment of the K matrix, and show that electronic interactions dominate not only the dissociative recombination but also the vibrational relaxation induced by slow electrons. Most of our rate coefficients for dissociative recombination are in good agreement with the measurements at the TSR storage ring [S. Krohn et al., Phys. Rev. A 62, 032713 (2000)]. On the contrary, our rates for vibrational deexcitation, close to former results obtained by R-matrix calculations [B. K. Sarpal and J. Tennyson, Mon. Not. R. Astron. Soc. 263, 909 (1993)], are smaller by up to one order of magnitude than the experimental values which are deduced from the time evolution of the vibrational populations, measured by the Coulomb explosion imaging method.

Authors:
 [1];  [2];  [3];  [1];  [4];  [5];  [6];  [1];  [7]
  1. Laboratoire de Photophysique Moleculaire, Universite Paris-Sud, Bat. 210, F-91405 Orsay, (France)
  2. (CEPAMOQ), Universite de Douala, BP 24157 Douala, (Cameroon)
  3. Centre de Physique Atomique Moleculaire et Optique Quantique (CEPAMOQ), Universite de Douala, BP 24157 Douala, (Cameroon)
  4. (Romania)
  5. Foundation of Computer Science Laboratory, University of Aizu, Ikki, Aizuwakamatsu 965-8580, (Japan)
  6. Laboratoire de Mecanique, Physique et Geosciences, Universite du Havre, F-76058 Le Havre, (France)
  7. (France)
Publication Date:
OSTI Identifier:
20640178
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 68; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevA.68.032704; (c) 2003 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CROSS SECTIONS; DISSOCIATION; ELECTRON-MOLECULE COLLISIONS; ELECTRONS; ENERGY TRANSFER; EXCITATION; HYDROGEN IONS 2 PLUS; K MATRIX; R MATRIX; RECOMBINATION; RELAXATION; TSR STORAGE RING; VIBRATIONAL STATES

Citation Formats

Ngassam, V., Centre de Physique Atomique Moleculaire et Optique Quantique, Motapon, O., Florescu, A., Institute for Space Science, P.O. Box MG-36, 76900 Bucharest,, Pichl, L., Schneider, I. F., Suzor-Weiner, A., and Laboratoire de Chimie Physique, Universite Paris VI, Paris,. Vibrational relaxation and dissociative recombination of H{sub 2}{sup +} induced by slow electrons. United States: N. p., 2003. Web. doi:10.1103/PhysRevA.68.032704.
Ngassam, V., Centre de Physique Atomique Moleculaire et Optique Quantique, Motapon, O., Florescu, A., Institute for Space Science, P.O. Box MG-36, 76900 Bucharest,, Pichl, L., Schneider, I. F., Suzor-Weiner, A., & Laboratoire de Chimie Physique, Universite Paris VI, Paris,. Vibrational relaxation and dissociative recombination of H{sub 2}{sup +} induced by slow electrons. United States. doi:10.1103/PhysRevA.68.032704.
Ngassam, V., Centre de Physique Atomique Moleculaire et Optique Quantique, Motapon, O., Florescu, A., Institute for Space Science, P.O. Box MG-36, 76900 Bucharest,, Pichl, L., Schneider, I. F., Suzor-Weiner, A., and Laboratoire de Chimie Physique, Universite Paris VI, Paris,. Mon . "Vibrational relaxation and dissociative recombination of H{sub 2}{sup +} induced by slow electrons". United States. doi:10.1103/PhysRevA.68.032704.
@article{osti_20640178,
title = {Vibrational relaxation and dissociative recombination of H{sub 2}{sup +} induced by slow electrons},
author = {Ngassam, V. and Centre de Physique Atomique Moleculaire et Optique Quantique and Motapon, O. and Florescu, A. and Institute for Space Science, P.O. Box MG-36, 76900 Bucharest, and Pichl, L. and Schneider, I. F. and Suzor-Weiner, A. and Laboratoire de Chimie Physique, Universite Paris VI, Paris,},
abstractNote = {We present calculations of cross sections and rate coefficients for the dissociative recombination of H{sub 2}{sup +} ions initially in v=0-6 vibrational levels, together with rate coefficients for the competing electron-induced vibrational deexcitation. We used the multichannel quantum defect theory with a second-order treatment of the K matrix, and show that electronic interactions dominate not only the dissociative recombination but also the vibrational relaxation induced by slow electrons. Most of our rate coefficients for dissociative recombination are in good agreement with the measurements at the TSR storage ring [S. Krohn et al., Phys. Rev. A 62, 032713 (2000)]. On the contrary, our rates for vibrational deexcitation, close to former results obtained by R-matrix calculations [B. K. Sarpal and J. Tennyson, Mon. Not. R. Astron. Soc. 263, 909 (1993)], are smaller by up to one order of magnitude than the experimental values which are deduced from the time evolution of the vibrational populations, measured by the Coulomb explosion imaging method.},
doi = {10.1103/PhysRevA.68.032704},
journal = {Physical Review. A},
number = 3,
volume = 68,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2003},
month = {Mon Sep 01 00:00:00 EDT 2003}
}
  • Using the multichannel quantum defect theory (MQDT), dissociative recombination of H/sup +//sub 2/, HD/sup +/, and D/sup +//sub 2/ via the two-electron excited superexcited state /sup 1/..sigma../sub g/(2psigma/sub u/)/sup 2/ is studied for each specified initial vibrational state v/sub i/ (approx. <4) of molecular ions at low electron energies 0.02approx.
  • Dissociative recombination of H/sub 2//sup +/ by collisions with slow electrons is investigated by the multichannel quantum defect theory. (AIP)
  • Cross sections for the dissociative recombination of electrons and H/sub 2//sup +/ ions having low internal energies have been measured by means of the merged electron-ion beam technique. Narrow resonances associated with indirect capture into high-lying Rydberg states of the neutral molecule have been found. The use of ions with only two vibrational states significantly populated has allowed the high-resolution capability of the merged-beam technique to be clearly demonstrated
  • A novel technique using a flowing afterglow-Langmuir probe apparatus for measurement of temperature dependences of rate constants for dissociative recombination (DR) is presented. Low ({approx}10{sup 11} cm{sup -3}) concentrations of a neutral precursor are added to a noble gas/electron afterglow plasma thermalized at 300-500 K. Charge exchange yields one or many cation species, each of which may undergo DR. Relative ion concentrations are monitored at a fixed reaction time while the initial plasma density is varied between 10{sup 9} and 10{sup 10} cm{sup -3}. Modeling of the decrease in concentration of each cation relative to the non-recombining noble gas cationmore » yields the rate constant for DR. The technique is applied to several species (O{sub 2}{sup +}, CO{sub 2}{sup +}, CF{sub 3}{sup +}, N{sub 2}O{sup +}) with previously determined 300 K values, showing excellent agreement. The measurements of those species are extended to 500 K, with good agreement to literature values where they exist. Measurements are also made for a range of C{sub n}H{sub m}{sup +} (C{sub 7}H{sub 7}{sup +}, C{sub 7}H{sub 8}{sup +}, C{sub 5}H{sub 6}{sup +}, C{sub 4}H{sub 4}{sup +}, C{sub 6}H{sub 5}{sup +}, C{sub 3}H{sub 3}{sup +}, and C{sub 6}H{sub 6}{sup +}) derived from benzene and toluene neutral precursors. C{sub n}H{sub m}{sup +} DR rate constants vary from 8-12 Multiplication-Sign 10{sup -7} cm{sup 3} s{sup -1} at 300 K with temperature dependences of approximately T{sup -0.7}. Where prior measurements exist these results are in agreement, with the exception of C{sub 3}H{sub 3}{sup +} where the present results disagree with a previously reported flat temperature dependence.« less
  • We discuss the low-energy dissociative recombination of H{sup +}{sub 3} , which strongly influences the abundance of this ion in diffuse interstellar molecular clouds. The kinetic couplings between the ionization continuum and the dissociative ground state of H{sub 3} have been used as input to a two-dimensional wave packet calculation of dissociation dynamics. The cross section obtained for direct dissociative recombination is much smaller than the latest experimental results. However, a multichannel quantum defect treatment shows that an indirect mechanism via bound Rydberg states of H{sub 3} prevails for this process.