Second-kind collisions of electrons with excited Cd+, Ca+, Ga+, Tl+and Pb+ions

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Abstract
The collisions of thermal energy electrons which cause de-excitation of excited states of some metal ions are studied experimentally using flowing afterglow techniques. For all levels whose calculated radiative lifetimes exceed 100 ns, the effects of these collisions are apparent at electron densities of order 1013 cm-3 as a destruction rate competitive with radiative decay. Large rate constants of order 10-5cm3s-1 are deduced. The theoretical basis of the temperature variation of collision rates is examined and it is shown that deexcitation rates are much less sensitive to electron temperatures than are the corresponding excitation rates. The results of this study have implications for the future development of metal-ion lasers because susceptibility of collisional depopulation of the upper level is reflected in the saturation behaviour of the laser transition.