Low-energy electron scattering from molecular hydrogen: Excitation of the X1Σg+ to b

Mateusz Zawadzki

¹

,

R. M. Wright

²

,

G. Dolmat

³

et al.

Abstract

We present time-of-flight differential cross section measurements and convergent close-coupling calculations of differential cross sections for the electron impact excitation of the X 1 Σ g + → b 3 Σ u + transition in molecular hydrogen. A part of this work was recently published in [Zawadzki et al. Phys. Rev. A 97, 050702(R) (2018)]. In this work, agreement between theory and experiment is excellent overall, and marks a transition in electron-molecule scattering where differential scattering of excitation is found to be in such precise agreement. We also present total electron impact excitation differential cross sections for H 2 for which agreement between theory and experiment is found to be excellent.

Benchmark calculations of electron impact electronic excitation of the hydrogen molecule

“…DCS for the X 1 Σ + g → b 3 Σ + u transition. Comparison of the UKRMol+ and MCCC calculations with the measurements ofZawadzki et al (2018).…”

Experimental determination of H2 mass stopping powers for low-energy electrons

“…1). The apparatus and procedure used have been described in detail elsewhere, e.g., in the work of Zawadzki et al [2], so only a brief summary of it is given here. The electron scattering experiment consisted of a pulsed electron gun which produced a collimated electron beam incident onto a collimated gas target effusing perpendicularly from a sooted molybdenum hypodermic needle of length 2.25 cm and outer and inner diameter of 1 mm and 0.8 mm, respectively.…”

“…The TOF differential cross section (DCS) scattering data were taken at E 0 values of: 11, 11.5, 12, 12.5, 13.5, 14, 15, 15.5, 16, 17.5, 20 and 25 eV and are detailed in [2]. These were obtained by normalizing the elastic scattering feature in the TOF spectra to the elastic DCSs obtained from Muse et al [40], again discussed in [2]. Figure 2 shows a typical energy loss spectra for 15, 20 and 25 eV incident electron energy recorded at θ = 90 • .…”

“…Another important note to make here is that above the ionization energy (I p ) of H 2 at 15.43 eV [37], the spectrum contains not only contributions from scattered energy loss electrons, but also continuum electrons which add to the "E L " signal, and so the detected ionization energy loss continuum is raised due to continuum electrons. To counteract this to a first-order, we have reduced the continuum by a factor of 2, as this tends to make our ionization DCSs in significantly better agreement with theory is discussed, justified and illustrated in [2]. At E 0 close to I p (e.g.…”

“…Molecular hydrogen, the simplest molecule, has been the topic of extensive collision studies both theoretically as well as experimentally [1,2,[4][5][6][7][8]. H 2 is a prevalent species in natural and man-made plasmas, which are important to the study of universal phenomena, such as stellar emission, planetary aurorae, fusion and formation of H 2 O and life [9].…”