Stimulated Raman excitation of the ortho-H-2-OH entrance channel complex

The fundamental H-2 vibration of the ortho-H-2-OH complex in its ground ele ctronic state has been observed at 4151.49+/-0.03 cm(-1) via stimulated Ram an excitation. The stimulated Raman transition has been identified with an ultraviolet probe laser using two different detection schemes. The transiti on was detected as a depletion in the H-2-OH laser-induced fluorescence sig nal in the OH A (2)Sigma(+) - X (II)-I-2 (1,0) spectral region and through the appearance of OH A (2)Sigma(+) - X (II)-I-2 (0,1) laser-induced fluores cence following vibrational predissociation of the complex. Vibrational pre dissociation is found to proceed via a near-resonant pathway that transfers one quantum of vibrational excitation from H-2 to OH. The remaining simila r to 529 cm(-1) of available energy is distributed over excited rotational states of OH (v = 1) and the lowest rotational level of ortho-H-2 (v = 1), with the balance flowing into translational recoil. The lifetime of vibrati onally activated ortho-H-2-OH (nu(H2) = 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 studie s of OH vibrational activation in ortho-H-2-OH as well as full collision st udies of the reaction of vibrationally excited H-2 with OH. (C) 1999 Americ an Institute of Physics.