Infrared Spectrum of the Ar−NH2+ Ionic Complex

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Rotationally resolved infrared spectra of the ν 1 and ν 3 N−H stretching vibrations of the Ar−NH 2 + radical ionic complex have been observed by means of photodissociation spectroscopy. The analysis of the rotational structure shows that the complex has a 3 Σ - ground electronic state with a linear or quasi-linear proton-bound structure Ar−H−N−H + characterized by an intermolecular center of mass separation of 3.085 Å. The origins of the ν 1 and ν 3 bands were determined as 2803.65(2) and 3287.36(2) cm -1, and the frequency of the intermolecular stretch vibration, ν s, as 170.4(6) cm -1 . Ab initio calculations performed at the UMP2 level of theory confirm that the quasi-linearity and the diradical character of NH 2 + in its electronic ground state are not changed upon Ar complexation. The calculated properties of the intermolecular bond of the complex ( D e = 1773 cm -1, R Ar - H ∼ 2.01 Å, ν s ∼ 185 cm -1 ) and the predicted complexation induced frequency shifts for ν 1 and ν 3 are in good agreement with the experimental results.