Stimulated Raman excitation of the ortho-H_2-OH entrance channel complex

摘要

The fundamental H_2 vibration of the ortho-H_2-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 H_2-OH laser-induced fluorescence signal in the OH A~2#SIGMA#~+ - X~2#PI# (1,0) spectral region and through the appearance of OH A~2#SIGMA#~+ - X~2#PI# (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 H_2 to OH. The remaining approx 529 cm~(-1) of available energy is distributed over excited rotational states of OH (#upsilon# = 1) and the lowest rotational level of ortho-H_2 (#upsilon# = 1), with the balance flowing into translational recoil. The lifetime of vibrationally activated ortho-H_2-OH (#nu#_(H_2) = 1) is determined to the 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-H_2-OH as well as full collision studies of the reaction of vibrationally excited H_2 with OH.