Absolute emission cross sections for electron-impact excitation ofZn+(4p P2)and (5s S2) terms. I

Abstract

Absolute emission cross sections for electron-impact excitation of the $3d^{10}4p {}_{}{}^2{}_{}{}^{}P$ and $3d^{10}5s {}_{}{}^2{}_{}{}^{}S$ terms of ${\mathrm{Zn}}^{+}$ have been measured from below threshold to about 790 eV (${}_{}{}^2{}_{}{}^{}P$) and 388 eV (${}_{}{}^2{}_{}{}^{}S$) using the crossed-charged-beams technique. Both transitions have the abrupt onset at threshold characteristic of positive-ion excitation. The ${}_{}{}^2{}_{}{}^{}P$ cross section shows considerable structure in the interval from threshold to near 20 eV, above which it falls off smoothly. Agreement with five-state close-coupling theory is excellent below 100 eV when cascading is included in the theory. Above 100 eV, the data lie above the theory. The peak value of the ${}_{}{}^2{}_{}{}^{}P$ cross section is 9.4×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ essentially at threshold, while the peak value of the ${}_{}{}^2{}_{}{}^{}S$ cross section is about 0.47×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$. The net linear polarization of the $3d^{10}4p {}_{}{}^2{}_{}{}^{}P$ emission was measured (unresolved from the $3d^{10}4d {}_{}{}^2{}_{}{}^{}D\to 3d^{10}4p {}_{}{}^2{}_{}{}^{}P$ cascading transition), and these data were used to correct the cross-section data for anisotropy of the emitted light. The effective lifetime of the $3d^{9}4s^2{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ level was measured by observing exponential decay of the 589.6-nm photons resulting from its decay.