15min:

O. DOPFER, S. A. NIZKORODOV, R. V. OLKHOV, J. P. MAIER, Institut für Physikalische Chemie, Universität Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland; AND K. HARADA, Institute for Molecular Science, Myodaiji, Okazaki, 444-8585 Japan.

Rotationally resolved infrared spectra of the ₁ and ₃ N-H stretching vibrations of the Ar-HNH⁺ radical ionic complex have been observed by means of photodissociation spectroscopy. The analysis of the rotational structure shows that the complex has a ^{3 -} 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 ₁ and ₃ bands were determined as 2803.65(2) and 3287.36(2) cm^-1, and the frequency of the intermolecular stretch vibration, _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 HNH⁺ 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, _s 185 cm^-1) and the predicted complexation induced frequency shifts for ₁ and ₃ are in good agreement with the experimental results.