Associative ionization in mercury

Summary form only given, as follows. Ionization in binary collisions of 6/sup 3/P/sub 0,1,2/ excited mercury atoms are of particular importance for the charge particle balance in low temperature mercury-rare gas plasmas, which have found wide and successful application in fluorescent lamps. The principal weak point of existing theoretical models of lighting plasmas is the choice of processes assumed to lead to ionization in collisions of 6/sup 3/P atoms of mercury, and hence to large uncertainties in the cross-section and rate constant data. In fact, the cross-section values used in discharge models differ by more than a factor of ten. Binary 6/sup 3/P/sub 0/ collisions, usually neglected, are expected to be of great importance. We present numerical results from the GLOMAC model, showing the variation in fluorescent lamp operating characteristics as the rate constants for ionization in collisions of 6/sup 3/P atoms are varied through the range allowed by existing experimental results. The notable dependencies observed illustrate the need for more accurate experimental data. Direct experimental observation of the collisional processes is hampered by the difficulty of optically exciting the 6/sup 3/P/sub 0,2/ levels directly from the ground state. A novel experimental approach to the measurement of absolute collisional ionization cross-sections, based on a radio frequency ion trap, is proposed. The sensitivity of the method is expected to be three or four orders of magnitude better than that of conventional techniques. This provides new opportunities to study collisional ionization processes of metastable atoms optically exciting directly from the ground state.