Photon and electron ionization of the HeH + Molecule
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Photon and electron ionization of the HeH+ Molecule Michael Stuart Pindzolaa and Dennis Bodewits Department of Physics, Auburn University, Auburn, AL, USA Received 14 May 2020 / Received in final form 30 June 2020 Published online 3 September 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. With the first detection of HeH+ in nearby interstellar space, various molecular ionization and recombination processes are now being calculated to better understand the dynamics of the first molecule in the universe. We use a configuration-average distorted-wave method to compute the photon and electron ionization cross sections of HeH+ based on an earlier molecular structure tabulation.
1 Introduction Recently the first observations of the HeH+ molecular ion were reported to be found in the planetary nebula NGC 7027 [1]. In the early universe the first molecular bond was formed in HeH+ through the radiative association of He and protons. The creation of HeH+ created a path to the formation of H2 . Based on advances in terahertz spectroscopy [2,3] and a high-altitude observatory [4], HeH+ has finally been discovered. The configuration-average distorted-wave (CADW) method [5] has been found to be quite useful in calculating both photon and electron ionization cross sections of diatomic molecules. Calculations using the CADW method were recently made for the photon ionization of CO [6] and were found to be in good agreement with time of flight spectrometer measurements [7], and also for the photon ionization of NO [6] which were also found to be in good agreement with time of flight spectrometer measurements [8]. Calculations using the CADW method were recently made for the electron ionization of CN+ [9] and were found to be in fairly good agreement with crossedbeams measurements [10]. Calculations using the CADW method have also recently been made for both the photon and electron ionization of BeH [11]. The photon ionization cross sections were found to be larger than previous molecular-adapted quantum defect orbital calculations [12], while the electron ionization cross sections were also found to be larger than previous Deutsch-Mark and binary encounter Bethe calculations [13]. The larger photon and electron ionization CADW cross sections were attributed to the inclusion of both the 3σ and 2σ subshells. In this paper we carry out CADW calculations for both the photon and electron ionization of HeH+ at an internuclear separation of R = 1.455. Resonant states found in the photon ionization of HeH+ were first invesa
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tigated using the R-matrix method by Tennyson [14]. Subsequently photon ionization calculations [15–17] were carried out for the HeH+ molecular ion. The photon ionization calculations for HeH+ are compared to those reported by Fernandez and Martin [17]. The rest of the paper is structured as follows: in Section 2 we review the configuration-average distorte
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