Collisional deexcitation of metastable ions: A new technique to separate radiative and nonradiative contributions

A method is presented to measure separate cross sections for collisional deexcitation of metastable ions via radiative and non-radiative processes. The principle of the experiment is to first determine the total collisional deexcitation cross section in an attenuation measurement. After this the non-radiative part is determined separately in a measurement where the ionized target atom (unique to the non-radiative process) is detected. Here, we discuss recently published results on deexcitation of metastable He+(2s) ions colliding with Ar at 1.65 keV/amu (1, 2) as well as preliminary results for Xe and H2 targets. In all cases we find that the dominating contribution from radiative deexcitation agrees with the result of a semi-classical calculation of the 2s-2p mixing driven by the induced dipole field of the target atom or molecule modified by taking competing processes, for which we measured the cross sections, into account. Further, the observed time-of-flight spectra with the molecular target H2 are di...