Ionization processes in fluorescent lamps: evaluation of the Hg chemi-ionization rate coefficients

Chemi-ionization by two mercury atoms to produce mercury atomic and molecular ions has been considered an important process in fluorescent lamps (FLs) for a quarter of a century. Despite the absence of reliable data, these processes have been included in a number of numerical models to help explain some of the experimental observations. These models have shown that the most important process is the Penning ionization of two Hg metastable atoms Hg(6(3)P2)+Hg(6(3)P2) --> Hg(+)+Hg(6(1)S0)+e. Although there is no experimental measurement of this cross section, modelers have typically used values implied from measurements of other chemi-ionization cross sections, or values obtained by fitting parameters to numerical models to obtain agreement with experiment. Recent theoretical investigations have indicated that the cross sections for the important processes may not be as large as previously thought. The aim of the present paper is to critically review the historical development of studies of chemi-ionization in fluorescent lamps and to present new experimental evidence which is consistent with the theoretical calculations and contradicts the conclusions from previously published experiments.