Stimulated Raman excitation of the ortho-H2–OH entrance channel complex

Abstract

The fundamental H2 vibration of the ortho-H2–OH complex in its ground electronic state has been observed at 4151.49±0.03 cm−1 via stimulated Raman excitation. The stimulated Raman transition has been identified with an ultraviolet probe laser using two different detection schemes. The transition was detected as a depletion in the H2–OH laser-induced fluorescence signal in the OH A 2Σ+–X 2Π (1,0) spectral region and through the appearance of OH A 2Σ+–X 2Π (0,1) laser-induced fluorescence following vibrational predissociation of the complex. Vibrational predissociation is found to proceed via a near-resonant pathway that transfers one quantum of vibrational excitation from H2 to OH. The remaining ∼529 cm−1 of available energy is distributed over excited rotational states of OH (v=1) and the lowest rotational level of ortho-H2 (v=1), with the balance flowing into translational recoil. The lifetime of vibrationally activated ortho-H2–OH (νH2=1) is determined to be less than 7 ns, the temporal resolution of the lasers, by monitoring the time evolution of the OH products. The results are compared with previous infrared studies of OH vibrational activation in ortho-H2–OH as well as full collision studies of the reaction of vibrationally excited H2 with OH.