Half-collision studies of the Hg–NH3 excimer

Abstract

The Hg–NH3 complex has been studied by forming the complex in a supersonic jet and probing the bound-to-bound transitions to the two excited electronic states correlated to Hg(6 3P1)+NH3. Laser-induced fluorescence and action spectroscopy have been combined with isotopic studies to map out the characteristics of these states. Both excited states are found to be bound by more than 5000 cm−1, over 20 times greater than the ground state binding energy. Extensive vibrational structure is found and interpreted in terms of a stretching progression of the Hg–NH3 bond and bending of the NH3 moiety with respect to the mercury atom. The two states show striking differences in their behavior with respect to predissociation to Hg(6 3P0). The B̃ state is not observed in fluorescence, but predissociates efficiently to Hg(3P0)+NH3, while the à state shows predominant fluorescence with only a minor amount of Hg(6 3P0) formation. Rotational band contour analysis has been used to assign the B̃ state as the 3E and the à state as the 3A1 state. Both states are characterized by a shortening in the Hg–N bond distance from 3.35 Å in the ground state to about 2.2 Å in either excited state. The rotational contour assignments show that the electronic angular momentum of the excited mercury atom is preserved in the complex despite the complex’s polyatomic nature. This allows an interpretation of the electronic relaxation in a quasidiatomic fashion. All our results are consistent with a C3v geometry for the Hg–NH3 complex in both the ground and excited states. The characteristics of the à and B̃ states and their couplings to the ã state correlated to 3P0 enable a comparison with the full-collision studies and has led us to postulate the à and B̃ states as the source of the luminescence observed in those studies.