Laser-induced fluorescence from theF0−state of the HgZn excimer

The relative intensities of the vibrational components in the laser-induced fluorescence spectrum arising from a particular molecular vibronic state are usually independent of the exciting wavelength and thus do not depend on the lower vibronic state from which the excitation takes place. We have observed that although the intensity pattern in the fluorescence spectrum from the E$0^{\mathrm{-}}$(v’=0) level is independent of the excitation wavelength, the relative intensities of the bands in the fluorescence spectrum from the E$0^{\mathrm{-}}$(v’=1) level do depend on the wavelength of the exciting light. We have also observed that the vibrational intensity distribution in the excitation spectrum of the E$0^{\mathrm{-}}$(v’=1) level depends on the fluorescence wavelength at which it is monitored, whereas the intensity profile in the excitation spectrum of the E$0^{\mathrm{-}}$(v’=0) level is independent of the monitoring wavelength. These variations in the vibrational intensity patterns suggest that the intensities may arise from the sum of two Franck-Condon factors in some of the vibrational bands. This phenomenon is ascribed to the presence of a second upper state, the F$0^{\mathrm{-}}$ state, whose v’=0 level almost coincides with the v’=1 level of the E$0^{\mathrm{-}}$ state and which has substantial probabilities of transitions to the A1, A$0^{\mathrm{-}}$, and B$0^{\mathrm{-}}$ states.