Insights on the CN B 2Σ+ + Ar potential from ultraviolet fluorescence excitation and infrared depletion studies of the CN–Ar complex

Abstract

UV laser-induced fluorescence and IR-UV fluorescence depletion studies have been used to characterize the intermolecular levels of the CN-Ar complex in the excited state correlating with CN B (2)Σ(+) + Ar. Additional CN-Ar features are identified to lower wavenumber than reported previously. Fluorescence depletion spectra are recorded to confirm that these CN-Ar features and other higher energy features in the B-X spectrum originate from a common ground state level. The UV depletion is induced by IR excitation of CN-Ar from the ground state zero-point level to a hindered internal rotor state (n(K) = 1(1)) in the CN overtone region. The lowest energy feature in the B-X spectrum at 25,714.1 cm(-1) is assigned as a transition to the zero-point level of the B state and also yields its binding energy, D(0) = 186(2) cm(-1), which is in excellent accord with theoretical predictions. The next feature approximately 40 cm(-1) higher is attributed to overlapping transitions to intermolecular levels with bend (v(b)(K)=1(1)) or stretch (v(s) = 1) excitation. Yet higher features (previously reported) are also assigned, based on their transition type and wavenumber, which are consistent with the intermolecular energy level pattern computed theoretically. Finally, the intensity profile of the lowest energy features in the B-X spectrum reflects the predicted change in the CN (B (2)Σ(+), X (2)Σ(+)) + Ar potentials upon electronic excitation from a weakly anisotropic potential about the linear N≡C-Ar configuration in the ground state to a more strongly bound linear C≡N-Ar structure in the excited B electronic state.