Linear and centrosymmetric N-2 center dot center dot center dot Ar+center dot center dot center dot N-2

A high resolution infrared absorption spectrum of the ionic complex N-2... Ar+... N-2 has been observed by tunable diode laser spectroscopy through a supersonic planar plasma. Seventy-six rovibrational transitions were measur ed involving excitation of the antisymmetric NN (nu(3)) stretching fundamen tal. The band origin is at 2288.7272(2) cm(-1) and the ground state rotatio nal constant is determined as B-0=0.034 296(7) cm(-1). The spectrum shows a clear spin-statistical intensity alternation and is consistent with a line ar and centrosymmetric equilibrium geometry and a ground state with (2)Sigm a(u)(+) symmetry. The charge is predominantly located on the argon atom. Th e assignment is supported by high level ab initio calculations carried out. The best estimate for the equilibrium geometry is R-e(NN)=1.1014 Angstrom and r(e)(Ar ... N)=2.3602 Angstrom, yielding B-e=0.034 297 cm(-1). The equi librium dissociation energy D-e for fragmentation into N-2 and [ArN2](+) is calculated to be similar to 1.7 eV. (C) 2000 American Institute of Physics . [S0021-9606(00)01627-5].