INFRARED PREDISSOCIATION SPECTRA OF NE-N-HN2-5)( CLUSTERS (N=1)

Infrared predissociation spectra of Ne-n-HN2+ (n = 1-5) cluster ions h ave been recorded in the vicinity of the N-H stretching vibration (nu( 1)) of HN2+. Several bands of the Ne-HN2+ dimer are rotationally resol ved and provide direct information on the geometry, intermolecular str etching and bending frequencies, and complexation induced frequency sh ift of the nu(1) vibration. The Ne-HN2+ complex has a linear, proton b ound structure with an average separation between the Ne atom and the HN2+ center-of-mass of [1/R-2](-1/2)=3.28 Angstrom. The observed chara cteristics of the dimer are reproduced by a two-dimensional intermolec ular potential energy surface calculated at the MP2 level, that is adi abatically corrected to account for the coupling of the intramolecular N-H stretching and intermolecular motions. The binding energy in the vibrational ground slate of the complex is found to be 795 cm(-1) and increases to 1005 cm(-1) upon excitation of the N-H stretching vibrati on. Although the spectra of the larger complexes are not rotationally resolved, shifts in the nu(1) transition frequency suggest that the la rger clusters possess structures where the Ne atoms are weakly attache d to the side of a linear Ne-HN2+ core. (C) 1998 American Institute of Physics. [S0021-9606(98)00521-2]