Spectroscopic studies of the charge-transfer reactionHe++ Hg→He + (Hg+)* at thermal energy

The reaction ${\mathrm{He}}^{+}$ + Hg→He + (${\mathrm{Hg}}^{+}$)* has been studied at thermal energy in a drift-tube-mass-spectrometer apparatus fitted with a sapphire window for observing the light emitted from the electronically excited ions. Over the wavelength range 300-900 nm, the only emissions observed from the (${\mathrm{Hg}}^{+}$)* product ions are the 614.9-nm ($7p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\to 7s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$) and 794.4-nm ($7p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\to 7s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$) transitions, in approximately equal amounts. This equal branching in the case of reaction paths having substantially different energy defects, $\Delta \epsilon \left(\infty \right)=0.27\mathrm{} \mathrm{and} 0.72$ eV, respectively, is not explained by present theoretical models of the charge-transfer process.