Intermolecular vibrations and relaxation dynamics in complexes of OH a²∑⁺ (v′=0,1)with N₂

The intermolecular vibrational energy levels supported by the OH A ²∑⁺ (ν′=0,1)+N₂ potentials have been characterized spectroscopically through excitation of OH-N₂ complexes in the OH A ²∑⁺ -X ²Π 0-0 and 1-0 spectral regions. At least 95 levels correlating with OH A ²∑⁺ (ν′=0)+N₂ are observed in fluorescence depletion experiments. OH-N₂ complexes prepared in these levels have lifetimes with lower limits ranging from 1.4 to 8 ps due to rapid electronic quenching which precludes their detection by laser-induced fluorescence. An onset of OH-N₂ laser-induced fluorescence occurs at the OH A ²∑⁺ (ν′=0)+N₂ dissociation limit, enabling determination of the ground and excited state binding energies at ∼250 and ≥1372 cm^-1, respectively. In the OH A-X 1-0 region, OH-N₂ transitions originating from a common ground state level to single or groups of intermolecular vibrational levels correlating with OH A 22+ ²∑⁺ (ν′ = 1)+N₂ are observed via laser-induced fluorescence and fluorescence depletion measurements. Comparison of the OH-N₂ spectra obtained in the OH A-X 0-0 and 1-0 regions reveals that vibrational excitation of OH A ²∑⁺ increases the OH-N₂ binding energy by 139 cm^-1. OH-N₂ complexes excited in the OH A-X 1-0 region undergo ultrafast dynamics (<200 fs) which give rise to extensive spectral line broadening. A kinetic model indicates that vibrational predissociation is the dominant decay channel for OH-N₂ prepared in the intermolecular levels derived from OH A ²∑⁺ (ν′ = 1)+N₂.