Measurements of Absolute Cross Sections for (e,H2) Collision Processes. Formation and Decay ofH2−Resonances

Abstract

Energy and angular dependences of the elastic and inelastic scattering of electrons from ${\mathrm{H}}_2$ have been measured in the energy range 10 to 16 eV and for scattering angles ranging from 10° to 120°. Three resonance series have been investigated starting at 11.30, 11.50, and 13.63 eV, respectively. The last two series decay preferentially into one single electronic channel, while the first resonance (resonance I) decays into all energetically possible exit channels, i.e., $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$, $b{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, $B{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$. Throughout, stress is laid on the importance of absolute cross sections and reported values, and excitation functions have been presented in absolute units. The cross sections for the elastic channel and some inelastic channels ($X{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, $v=1\mathrm{} \mathrm{and} 2$, and the dissociative continuum $b{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$) are composed of resonant and non-resonant scattering and show pronounced and rapidly changing interference structures. Relative branching ratios for resonance series I in terms of absolute total cross sections have been listed for those channels where practically no direct scattering amplitude is present. Summarizing those results, one can state that the probabilities (branching ratios) for the decay of resonance series I into the three electronic states $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$, $b{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, and $B{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ of the ${\mathrm{H}}_2$ molecule summed over all vibrational states of the exit channel are of the same order of magnitude. From the observed angular dependence of the scattered electrons, the configuration of the resonances has been determined and compared with existing theoretical predictions.