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Title: Radiative charge transfer in He{sup +}+ H{sub 2} collisions in the milli- to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches

Abstract

The paper presents a theoretical study of the low-energy dynamics of the radiative charge transfer (RCT) reaction He{sup +}({sup 2}S)+H{sub 2}(X{sup 1}{Sigma}{sub g}{sup +}){yields}He({sup 1}S)+H{sub 2}{sup +}(X{sup 2}{Sigma}{sub g}{sup +})+h{nu} extending our previous studies on radiative association of HeH{sub 2}{sup +} [F. Mrugala, V. Spirko, and W. P. Kraemer, J. Chem. Phys. 118, 10547 (2003); F. Mrugala and W. P. Kraemer, ibid. 122, 224321 (2005)]. The calculations account for the vibrational and rotational motions of the H{sub 2}/H{sub 2}{sup +} diatomics and for the atom-diatom complex formation in the reactant and the product channels of the RCT reaction. Continuum states of He{sup +}+ H{sub 2}(v= 0, j= 0) in the collision energy range {approx}10{sup -7}-18.6 meV and all quasi-bound states of the He{sup +}- H{sub 2}(para;v= 0) complex formed in this range are taken into account. Close-coupling calculations are performed to determine rates of radiative transitions from these states to the continuum and quasi-bound states of the He +H{sub 2}{sup +} system in the energy range extending up to {approx}0.16 eV above the opening of the HeH{sup +}+ H arrangement channel. From the detailed state-to-state calculated characteristics global functions of the RCT reaction, such as cross-section {sigma}(E), emission intensity I({nu},more » T), and rate constant k(T) are derived, and are presented together with their counterparts for the radiative association (RA) reaction He{sup +}({sup 2}S) +H{sub 2}(X{sup 1}{Sigma}{sub g}{sup +}){yields} HeH{sub 2}{sup +}(X{sup 2}A{sup Prime })+h{nu}. The rate constant k{sup RCT} is approximately 20 times larger than k{sup RA} at the considered temperatures, 0.1 {mu}K-50 K. Formation of rotational Feshbach resonances in the reactant channel plays an important role in both reactions. Transitions mediated by these resonances contribute more than 70% to the respective rates. An extension of the one-dimensional optical potential model is developed to allow inclusion of all three vibrational modes in the atom-diatom system. This three-dimensional optical potential model is used to check to which extent the state-to-state RCT rate constant is influenced by the possibility to access ground state continuum levels well above the opening of the HeH{sup +}+ H arrangement channel. The results indicate that these transitions contribute about 30% to the 'true' rate constant k{sup RCT} whereas their impact on the populations of the vibration-rotational states of the product H{sub 2}{sup +} ion is only minor. Present theoretical rate constant functions k{sup RCT}(T) obtained at different approximation levels are compared to experimental data: 1-1.1 Multiplication-Sign 10{sup -14} s{sup -1} cm{sup 3} at T= 15-35 K and {approx}7.5 Multiplication-Sign 10{sup -15} s{sup -1} cm{sup 3} at 40 K [M. M. Schauer, S. R. Jefferts, S. E. Barlow, and G. H. Dunn, J. Chem. Phys. 91, 4593 (1989)]. The most reliable theoretical values of k{sup RCT}, obtained by combining results from the state-to-state and the optical potential calculations, are between 2.5 and 3.5 times larger than these experimental numbers. Possible sources for discrepancies are discussed.« less

Authors:
 [1];  [2]
  1. Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, PL 87-100 Torun (Poland)
  2. Max-Planck-Institute of Astrophysics, Postfach 1317, D-85741 Garching (Germany)
Publication Date:
OSTI Identifier:
22105426
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 138; Journal Issue: 10; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BOUND STATE; CHARGE EXCHANGE; CROSS SECTIONS; DIATOMS; GROUND STATES; HELIUM; HELIUM IONS; HYDROGEN; HYDROGEN IONS 2 PLUS; ION-MOLECULE COLLISIONS; ONE-DIMENSIONAL CALCULATIONS; REACTION KINETICS; ROTATIONAL STATES; VIBRATIONAL STATES

Citation Formats

Mrugala, Felicja, and Kraemer, Wolfgang P. Radiative charge transfer in He{sup +}+ H{sub 2} collisions in the milli- to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches. United States: N. p., 2013. Web. doi:10.1063/1.4793986.
Mrugala, Felicja, & Kraemer, Wolfgang P. Radiative charge transfer in He{sup +}+ H{sub 2} collisions in the milli- to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches. United States. https://doi.org/10.1063/1.4793986
Mrugala, Felicja, and Kraemer, Wolfgang P. Thu . "Radiative charge transfer in He{sup +}+ H{sub 2} collisions in the milli- to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches". United States. https://doi.org/10.1063/1.4793986.
@article{osti_22105426,
title = {Radiative charge transfer in He{sup +}+ H{sub 2} collisions in the milli- to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches},
author = {Mrugala, Felicja and Kraemer, Wolfgang P.},
abstractNote = {The paper presents a theoretical study of the low-energy dynamics of the radiative charge transfer (RCT) reaction He{sup +}({sup 2}S)+H{sub 2}(X{sup 1}{Sigma}{sub g}{sup +}){yields}He({sup 1}S)+H{sub 2}{sup +}(X{sup 2}{Sigma}{sub g}{sup +})+h{nu} extending our previous studies on radiative association of HeH{sub 2}{sup +} [F. Mrugala, V. Spirko, and W. P. Kraemer, J. Chem. Phys. 118, 10547 (2003); F. Mrugala and W. P. Kraemer, ibid. 122, 224321 (2005)]. The calculations account for the vibrational and rotational motions of the H{sub 2}/H{sub 2}{sup +} diatomics and for the atom-diatom complex formation in the reactant and the product channels of the RCT reaction. Continuum states of He{sup +}+ H{sub 2}(v= 0, j= 0) in the collision energy range {approx}10{sup -7}-18.6 meV and all quasi-bound states of the He{sup +}- H{sub 2}(para;v= 0) complex formed in this range are taken into account. Close-coupling calculations are performed to determine rates of radiative transitions from these states to the continuum and quasi-bound states of the He +H{sub 2}{sup +} system in the energy range extending up to {approx}0.16 eV above the opening of the HeH{sup +}+ H arrangement channel. From the detailed state-to-state calculated characteristics global functions of the RCT reaction, such as cross-section {sigma}(E), emission intensity I({nu}, T), and rate constant k(T) are derived, and are presented together with their counterparts for the radiative association (RA) reaction He{sup +}({sup 2}S) +H{sub 2}(X{sup 1}{Sigma}{sub g}{sup +}){yields} HeH{sub 2}{sup +}(X{sup 2}A{sup Prime })+h{nu}. The rate constant k{sup RCT} is approximately 20 times larger than k{sup RA} at the considered temperatures, 0.1 {mu}K-50 K. Formation of rotational Feshbach resonances in the reactant channel plays an important role in both reactions. Transitions mediated by these resonances contribute more than 70% to the respective rates. An extension of the one-dimensional optical potential model is developed to allow inclusion of all three vibrational modes in the atom-diatom system. This three-dimensional optical potential model is used to check to which extent the state-to-state RCT rate constant is influenced by the possibility to access ground state continuum levels well above the opening of the HeH{sup +}+ H arrangement channel. The results indicate that these transitions contribute about 30% to the 'true' rate constant k{sup RCT} whereas their impact on the populations of the vibration-rotational states of the product H{sub 2}{sup +} ion is only minor. Present theoretical rate constant functions k{sup RCT}(T) obtained at different approximation levels are compared to experimental data: 1-1.1 Multiplication-Sign 10{sup -14} s{sup -1} cm{sup 3} at T= 15-35 K and {approx}7.5 Multiplication-Sign 10{sup -15} s{sup -1} cm{sup 3} at 40 K [M. M. Schauer, S. R. Jefferts, S. E. Barlow, and G. H. Dunn, J. Chem. Phys. 91, 4593 (1989)]. The most reliable theoretical values of k{sup RCT}, obtained by combining results from the state-to-state and the optical potential calculations, are between 2.5 and 3.5 times larger than these experimental numbers. Possible sources for discrepancies are discussed.},
doi = {10.1063/1.4793986},
url = {https://www.osti.gov/biblio/22105426}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 10,
volume = 138,
place = {United States},
year = {2013},
month = {3}
}