Intermolecular vibrations and relaxation dynamics in complexes of OH A 2Σ+ (v′=0,1) with N2

Abstract

The intermolecular vibrational energy levels supported by the OH A 2Σ+ (v′=0,1)+N2 potentials have been characterized spectroscopically through excitation of OH–N2 complexes in the OH A 2Σ+–X 2Π 0–0 and 1–0 spectral regions. At least 95 levels correlating with OH A 2Σ+ (v′=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 2Σ+ (v′=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 2Σ+ (v′=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 2Σ+ 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 2Σ+ (v′=1)+N2.