Interatomic potentials of singlet s-Rydberg series of a HgNe van der Waals dimer: Evidence for stabilization by superexchange interaction

Abstract

The interatomic potentials of the singlet Rydberg series of the HgNe dimer 1Σ+ Hg(n1S0)Ne (n=7–9) were determined over a wide range of interatomic distance by the analysis of the optical–optical double resonance (OODR) spectra measured in the present study via the A 3Π0+ and B 3Π1 states. The interatomic potential for n=7 consists of one bound vibrational level (v=0), three quasibound levels (v=1–3) trapped inside a potential barrier, and one weakly trapped quasibound level just above the potential barrier. The dissociation energy (De) of this potential is 50(3) cm−1 and the large potential barrier with a height of 133(2) cm−1 is located at 4.20(3) Å, while the interatomic potentials for n=8 and n=9 consist of a deep bound well, whose dissociation energies (De) are 240(3) and 297(3) cm−1, respectively. From these potentials, it was shown that the principal quantum number dependence (n) of the interatomic potential originates mainly from that of the exchange repulsion between the Rydberg electron of Hg and the attached Ne atom in a similar manner as the triplet Rydberg series of HgNe, 3Σ+ Hg(n3S1)Ne (n=7–10) [K. Onda et al. J. Chem. Phys. 101, 7290 (1994)]. By comparing the potentials of the singlet with the triplet Rydberg series, it was found that an interatomic potential of the singlet state is always deeper than that of the triplet state for the same n. This difference between singlet and triplet was interpreted by a superexchange interaction model [P. N. Anderson, Phys. Rev. 79, 350 (1950)], in which a singlet Rydberg state becomes more stable due to small spin density on the Ne atom induced by the kinetic exchange interaction between the Hg+ ion and the Ne atom.