Electron-impact study of the ${\mathrm{O}}_2$ molecule using the R-matrix method

We have computed elastic differential, momentum-transfer, excitation, ionization cross sections, collision frequencies, and scattering length for electron impact on the ${\mathrm{O}}_2$ molecule, which are computed using the R-matrix method. The results of the static exchange, correlated one-state, and 22-state close-coupling approximation are presented. We have detected a stable anionic bound state ${}^2{\Pi }_g$ of ${\mathrm{O}}_2{}^{-}$ and two shape resonances of ${}^2{\Pi }_u$ symmetry. The dissociative nature of these shape resonances is explored by performing scattering calculations in which the O-O bond is stretched. These resonances support dissociative attachment yielding O, ${\mathrm{O}}^{-}$ in dissociation of ${\mathrm{O}}_2$. Born correction is applied for higher partial waves neglected in the R-matrix calculations for elastic and dipole allowed transitions.

Figure 1

Electron-impact excitation cross sections from the ground state: $X{}^3{\Sigma }_g{}^{-}$ (${}^3{B}_{1g}$) of the ${\mathrm{O}}_2$ molecule to the $a{}^1{\Delta }_g$ $\left(a{}^1{A}_g{/}^1{B}_{1g}\right)$, solid line, present study; dash-dotted curve, Noble and Burke [10].

Figure 2

Electron-impact excitation cross sections from the ground state: $X{}^3{\Sigma }_g{}^{-}$ (${}^3{B}_{1g}$) of the ${\mathrm{O}}_2$ molecule to the $b{}^1{\Sigma }_g{}^{+}$ $\left(b{}^1{A}_g\right)$, solid line, present study; dash-dotted curve, Noble and Burke [10].

Figure 3

Electron-impact excitation cross sections from the ground $X{}^3{\Sigma }_g{}^{-}$ (${}^3{B}_{1g}$) state of the ${\mathrm{O}}_2$ molecule to the $B{}^3{\Sigma }_u^{-}$ (${}^3{A}_u$) state for 22 states calculation; dash-dotted curve, quartets; dashed curve, doublets; thin solid line, total sum (doublets + quartets); dotted curve, Born correction; thick solid line, Born corrected (sum of doublets, quartets and Born correction).

Figure 4

Variation of resonance width and position with bond length; solid blue curve, position of resonance (${}^2{\Pi }_u$); dashed red curve, width of resonance (${}^2{\Pi }_u$); dotted black curve, Higgins et al. [11].

Figure 5

Electron-impact BEB ionization cross sections of the ${\mathrm{O}}_2$ molecule; dashed red curve, Krishnakumar et al. (expt.) [14]; dotted cyan curve, Joshipura et al. (theoretical) [13]; dash-dotted blue curve, Kim et al. [36]; thick solid black line, our BEB model.

Figure 6

Differential cross sections (DCS) at 3 eV, 5 eV, 7 eV, and 9 eV for one-state CI model at $R_e$. red diamonds, Shyn and Sharp [17]; dashed blue curve, Sullivan et al. [15]; dotted cyan curve, Green et al. [18]; dash double-dotted magenta curve, Machado et al. [12]; solid black line, present results.

Figure 7

Momentum-transfer cross sections (MTCSs), at different energies, with spin average of ${\mathrm{O}}_2$ molecule ground state at one-state CI level. dash-dotted red curve, Machado et al. [12]; dotted cyan curve, Shyn and Sharp [17]; dashed blue curve, Sullivan et al. [15]; solid black line, present results.

Figure 8

Effective collision frequency as a function of electron temperature; dashed curve, $\overline{v}$; solid curve, $\langle v\rangle$.