Theoretical cross sections for H-on-Cs ionic and neutral reactions

Abstract

Potential-energy curves and coupling matrix elements have been calculated for the CsH and Cs${\mathrm{H}}^{+}$ systems. The potentials and coupling terms were employed in the coupled equations where the nuclear motion is described classically to obtain the energy dependence of the cross sections for energies 0.1-3.0 keV. The cross sections so obtained were: ${Q}_{+0}$ for the reaction ${\mathrm{H}}^{+}$ + Cs \ensuremath{\rightarrow} H + ${\mathrm{Cs}}^{+}$, ${Q}_{+m}$ for ${\mathrm{H}}^{+}+\mathrm{Cs}\ensuremath{\rightarrow}\mathrm{H}(2s)+{\mathrm{Cs}}^{+}$, ${Q}_{\ensuremath{-}0}$ for ${\mathrm{H}}^{\ensuremath{-}}$ + ${\mathrm{Cs}}^{+}$ \ensuremath{\rightarrow} H + Cs, and ${Q}_{0\ensuremath{-}}$ for $\mathrm{H}(1s)+\mathrm{Cs}\ensuremath{\rightarrow}{\mathrm{H}}^{\ensuremath{-}}+{\mathrm{Cs}}^{+}$. The CsH potential-energy curves were also used to estimate the ionization cross sections ${Q}_{\mathrm{i}\mathrm{o}\mathrm{n}\ensuremath{-}\mathrm{C}\mathrm{s}}$ for ${\mathrm{H}}^{\ensuremath{-}}+\mathrm{Cs}\ensuremath{\rightarrow}{\mathrm{H}}^{\ensuremath{-}}+{\mathrm{Cs}}^{+}+e$ and ${Q}_{\mathrm{i}\mathrm{o}\mathrm{n}\ensuremath{-}\mathrm{H}}$ for ${\mathrm{H}}^{\ensuremath{-}}+\mathrm{Cs}\ensuremath{\rightarrow}\mathrm{H}+\mathrm{Cs}+e$, and to yield an upper-limit cross section ${Q}_{m\ensuremath{-}}$ for the reaction $\mathrm{H}(2s)+\mathrm{Cs}\ensuremath{\rightarrow}{\mathrm{H}}^{\ensuremath{-}}+{\mathrm{Cs}}^{+}$. Semiempirical calculations were employed to obtain the deactivation cross section ${Q}_{\mathrm{mg}}$ for $\mathrm{H}(2s)+\mathrm{Cs}\ensuremath{\rightarrow}\mathrm{H}(2p)+\mathrm{Cs}$ where the product $\mathrm{H}(2p)$ rapidly radiates to $\mathrm{H}(1s)$. At 0.5 keV the theoretical cross sections obtained were ${Q}_{+0}=1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$, ${Q}_{+m}=5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$, ${Q}_{\ensuremath{-}0}=1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$, ${Q}_{0\ensuremath{-}}=8.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$, ${Q}_{\mathrm{i}\mathrm{o}\mathrm{n}\ensuremath{-}\mathrm{C}\mathrm{s}}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$, ${Q}_{\mathrm{i}\mathrm{o}\mathrm{n}\ensuremath{-}\mathrm{H}}=2.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$, ${Q}_{\mathrm{mg}}=8.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$, and ${Q}_{m\ensuremath{-}}\ensuremath{\le}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. For the reactions where experimental data is available, the theoretical cross sections are in satisfactory agreement with experiment except for ${Q}_{0\ensuremath{-}}$, where the theoretical values are approximately a factor of 5 larger than the experimental values.