Laser-induced fluorescence spectroscopy of theHg3excimer

We report what we believe to be the first observation of a laser-induced fluorescence band, excited by absorption from a low-lying state of the ${\mathrm{Hg}}_3$ excimer using a ‘‘pump-and-probe’’ method. A study of the fluorescence intensity as a function of the time separation between the ‘‘pump’’ and ‘‘probe’’ laser pulses provides clear evidence for the presence of both ${\mathrm{Hg}}_3$ and ${\mathrm{Hg}}_2$ molecules in the laser-excited mercury vapor. The fluorescence may be due to trimer emission or to dimer emission following dissociation of a trimer state.