A THEORETICAL-STUDY OF THE HGAR2(P-3(1)[-S-1(0)) VIBRONIC SPECTRUM

A quantum mechanical calculation of the vibronic spectrum of the HgAr2 van der Waals cluster in the region of the Hg(P-3(1) <-- S-1(0)) electronic transition is presented and compared with experiments. The potential energy surfaces for the ground and excited states are obtained using available empirical Ar-Ar and Ar-Hg potentials. For the ground electronic state, the potential is written as a sum of pairwise Ar-Ar and Ar-Hg(S-1(0)) interactions. On the contrary, for the electronically excited states correlating to Hg (P-3(1)), an axis switching rotation has to be applied to each individual Ar-Hg(P-3(1); OMEGA(e) = 0, +/- 1) interactions in order to define a common quantization axis. This results in a nonpairwise additive diabatic matrix Hamiltonian which after diagonalization provides the adiabatic excited potential energy surfaces. The vibrational wave functions associated to the ground and the first two (A and B) adiabatic electronically excited states are obtained by variational techniques using basis sets along Jacobi coordinates. Analysis of the wave functions reveals that the normal mode description is valid only for the very few first levels and that strong mode mixing prevails through all the rest of the spectrum. For the B+ state, the calculated and observed spectra compare well, while for the A state, some discrepancies are found. Possible reasons for these differences are discussed.