Infrared spectrum of the Ar-NH2+ ionic complex

Rotationally resolved infrared spectra of the nu(1) and nu(3) N-H stretchin g vibrations of the Ar-NH2+ radical ionic complex have been observed by mea ns of photodissociation spectroscopy. The analysis of the rotational struct ure shows that the complex has a (3)Sigma(-) ground electronic state with a linear or quasi-linear proton-bound structure Ar-H-N-H+ characterized by a n intermolecular center of mass separation of 3.085 Angstrom. The origins o f the nu(1) and nu(3) bands were determined as 2803.65(2) and 3287.36(2) cm (-1), and the frequency of the intermolecular stretch vibration, nu(s), as 170.4(6) cm(-1). Ab initio calculations performed at the UMP2 level of theo ry confirm that the quasi-linearity and the diradical character of NH2+ in its electronic ground state are not changed upon Ar complexation. The calcu lated properties of the intermolecular bond of the complex (D-e = 1773 cm(- 1), RAr-H similar to 2.01 Angstrom, nu(s) similar to 185 cm(-1)) and the pr edicted complexation induced frequency shifts for nu(1) and nu(3) are in go od agreement with the experimental results.