Vibrational Dynamics of Mass-Selected Ion Clusters as Studied by Double Resonance Laser Spectroscopy

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During the fiscal years of 1993 and 1994, I obtained the following results :(1) Excitation spectra for the transitions to the series of Rydberg states of Hg-rare gas type van der Waals clusters, HgNe and HgAr, were measured for the firast time by optical-optical laser double resonance (OODR) spectroscopy. Based on high-resolution measurements, isotope species of ^<200>HgNe and ^<202>HgNe were observed separately free from congestion by other less-abundant isotopic species of ^mHgNe (m=198,199,201, and 204) by using a well-split ro-vibronic transition to the A^30^+ state, which is an intermediate state for the double resonance scheme. Using the observed mass-selected OODR spectra, interatomic potentials of the s-and d-Rydberg series were detemined systematically.(2) It was found that the interatomic potential of the s-Rydberg state at a principal quantum number, n, of n=7 exhibits characteristic shape with a potential barrier. In order to interpret the potential function, an analysis using a quantum defect orbital was performed, and a potential model, representing well the n-dependence of the interatomic potential, was proposed. The potential model clearly showed that the n-dependence is principally govermed by an exchange interaction between a Rydberg electron and a rare gas atom attached to Hg. It was also shown that (i) inter atomic potentials of triplet and singlet electronic state are slightly different from each other for the same n and (ii) a triplet potential is always deeper than a singlet potential for the same n. This finding of the difference between the singlet and triplet states was interpreted for the first time by a super-exchange interaction. Furthermore, rates of the predissociation processes in the Rydberg states were also determined from the line-broadening of the high-resolution OODR spectra.