Resonant two-color photoionization threshold measurements of the Zn+(4s)center dot Ar bond strength: Model-potential analysis of M+(ns)center dot Ar interactions

The bond energy of the Zn(4s)(+). Ar ground-state ion has been determined t o be D-e = 2085 +/-100 cm(-1) by measuring the threshold for two-color reso nant photoionization of a ZnAr metastable state. This bond energy is larger (and the estimated bond length is smaller! than the values for other simil ar M(ns)(+). Ar states, where M = Mg, Ca, V, Co, Ba, Cd, and Hg, consistent with our earlier postulate that the Zn(4s)(+) "core'' is smaller than the other M(ns)(+) cores in the analogous electronically excited MAr van der Wa als complexes for M=Mg, Ca, Zn, Cd, and Hg. We analyze and compare the M+ ( ns). Ar potential curves using a model potential consisting of calculated 1 /R-4 (dipole induction) and 1/R-6 (quadrupole induction plus dispersion) at tractive terms, and an empirically derived Ae(-bR) repulsion term. The repu lsion term for Zn+ Ar is consistent with our postulate, in that at smaller R it is the least repulsive of the M+(ns). Ar repulsive potentials when M=Z n, Hg, V, Co, Cd, Mg, Ca, and Ba. (C) 1999 American Institute of Physics. [ S0021-9606(99)01213-1].