Experimental characterization of the CN X2Σ++Ar and H2 potentials via infrared-ultraviolet double resonance spectroscopy

The hindered internal rotor states (n(K) = 0(0), 1(1), and 1(0)) of the CN-Ar complex with two quanta of CN stretch (nu(CN) = 2), along with its ground state (nu(CN) = 0), have been characterized by IR-UV double resonance and UV spectroscopy. Analysis of rotationally structured bands enable n(K) assignments and reveal perturbations due to Coriolis coupling between two closely spaced hindered rotor states, n(K) = 1(1) and 1(0). A deperturbation analysis is carried out to derive accurate rotational constants and their associated CN center-of-mass to Ar bond lengths as well as the magnitude of the coupling. The energetic ordering and spacings of the CN-Ar hindered rotor states provide a direct experimental probe of the angular dependence of the CN X (2)Sigma(+) + Ar potential and permit radially averaged anisotropy parameters (V-10 = 5.2 cm(-1) and V-20 = 3.2 cm(-1)) to be determined. This analysis indicates a relatively flat potential about a linear N C-Ar configuration with a barrier to CN internal rotation of only similar to 12 cm(-1). The angular potentials determined from experiment and ab initio theory are in good accord, although theory predicts a higher barrier to CN internal rotation. A similar approach yields the infrared spectrum of H-2-CN in the CN overtone region, which exhibits a rotationally resolved Sigma <- Sigma parallel band that is consistent with theoretical predictions for ortho-H-2-CN. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723696]