Measurements of radiative charge-transfer reactions of doubly and singly charged rare-gas ions with rare-gas atoms at thermal energies

Radiative charge-transfer coefficients for single-electron transfer between doubly or singly charged noble-gas ions and noble-gas atoms have been determined at thermal energy using a drift-tube mass-spectrometer apparatus. At 300 K, k (He^2++He) = (4. 80. 5) 10^-14 cm^3/sec, with slightly smaller coefficients for the reactions Ne^2+ + Ne, Ar^2+ + Ar, Kr^2+ + Kr, and Xe^2+ + Xe. Differences in reactivity are found for the different, low-lying ^1S, ^1D, and ^3P states of the doubly charged ions. A three-body contribution to the radiative process is noted, with rate coefficients ranging between 10^-31 and 10^-30 cm^6/sec at 300 K for the different noble-gas systems. The radiative charge-transfer coefficients for singly ionized ions are somewhat smaller, k (He^++Ne) 110^-15 cm^3/sec and k (Ne^++Ar) 610^-15 cm^3/sec at 300 K. The measured value of k (He^2++He) is in reasonable agreement with the very recent theoretical calculations of Cohen and Bardsley.