VIBRATIONAL SPECTROSCOPY AND PREDISSOCIATION DYNAMICS OF THE ELECTRONICALLY EXCITED HGAR2 TRIATOMIC CLUSTER

Vibronic structures of the A-X and B-X bands of the HgAr2 triatomic cluster were investigated by laser-induced fluorescence (LIF) spectroscopy. The LIF spectra of the A-X and B-X bands of HgAr2 were observed free from hindrance of strong A-X and B-X transitions of HgAr by monitoring the fluorescence in the visible region. The analysis of the vibronic structures led to the fundamental frequencies of omega-1 = 26.3 (3), omega-2 = 12.0(5), and omega-3 = 28.1(4) cm-1 for the A state and omega-1 = 9.2(3) and omega-2 = 23.8(6) cm-1 for the B state, where subscripts "1," "2," and "3," respectively, denote symmetric stretching, bend, and asymmetric stretching modes. A number in parentheses represents an estimated limit of error (sigma). It was found that HgAr2 in the B state predissociates to produce HgAr(A)+Ar. The vibrational and rotational distributions of the HgAr fragment in the A state were derived by observing LIF spectra of the E-A band. Based on these distributions, level energies of HgAr2 in the B state were estimated with respect to those of HgAr in the A state, and then, the dissociation energies (D)e)) of HgAr2 to Hg + Ar + Ar were derived to be 374(2), 540(2), and 249(2) cm-1 for the X, A, and B states, respectively. The vibronic structure of HgAr2 in the lowest Rydberg (E) state associated with Hg(7(3)S1) was investigated by the optical-optical double resonance spectroscopy via the A state. The geometrical structure, in which an outer Ar atom is loosely bound to the Rydberg-type HgAr core, that is close to HgAr+, is proposed for the E state, and a presence of large amplitude motion of the outer Ar atom is deduced from the obtained fundamental frequencies of omega-1 = 102.1(3) and omega-2 = 5.4(2) cm-1, where subscripts "1" and "2" denote a stretching mode of the HgAr core and the Ar-Hg-Ar bending mode.