POTENTIAL-ENERGY SURFACE AND VIBRATIONAL ANALYSIS ALONG THE STRETCHING VIBRATIONS OF THE ARHAR+ ION

An ab initio calculated potential energy surface along the stretching coordinates of the linear ArHAr+ ion is presented. The potential surfa ce has been obtained using the MP2/15s11p3d1f/7s2p1d level of the ab i nitio electronic structure calculation theory. Qualitatively the poten tial is characterised by a development of double minimum structure at elongated Ar---Ar distances at higher vibrational energies and by a la rge amplitude for the motion of the hydrogen atom. The stretching vibr ational energy levels and wavefunctions have been calculated variation ally using harmonic oscillator basis functions. The vibrational analys is indicates extensive mixing of the zeroth-order harmonic oscillator vibrational states already at the bottom of the well giving rise to st rong absorption ''progression'' starting at 1208 cm(-1). The Einstein A coefficients for spontaneous emission transitions have also been cal culated and the IR emission spectrum is predicted to be particularly r ich in the 1100-1900 cm(-1) spectral region.