Electron capture into the 3 ${}_{}{}^3{}_{}{}^{}D$ state of He was measured by the detection of 5876-Å photons from the $3^3$D–2 ${}_{}{}^3{}_{}{}^{}P$ transition following collisions of ${\mathrm{He}}^{+}$ with various polyatomic molecules. The photon-emission cross section for this transition was measured for each target over the helium-ion energy range of 100 to 300 keV. The targets used were ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, CO, ${\mathrm{CO}}_2$, ${\mathrm{N}}_2$O, ${\mathrm{CH}}_4$, ${\mathrm{C}}_2$${\mathrm{H}}_2$, ${\mathrm{C}}_2$${\mathrm{H}}_4$, and ${\mathrm{C}}_2$${\mathrm{H}}_6$. For all targets, the cross sections could be fitted very well with a 1/$v^2$ function, where v is the helium-ion velocity.

• Received 13 December 1989

DOI:https://doi.org/10.1103/PhysRevA.41.2453