QUANTUM STATE-RESOLVED REACTIVE SCATTERING OF F-2 IN SUPERSONIC JETS - NASCENT HF(V,J) ROVIBRATIONAL DISTRIBUTIONS VIA IR LASER DIRECT ABSORPTION METHODS(H)

Supersonically cooled discharge radical atom sources are combined with high-sensitivity IR absorption methods to investigate state-to-state reactive scattering of F + n-H-2 --> HF(upsilon, J) + H in low-density crossed supersonic jets at center-of-mass collision energies of 2.4(6 ) kcal/mole. The product HF(upsilon, J) is probed with full vibrationa l and rotational quantum state selectivity via direct absorption of a single mode (Delta nu approximate to 0.0001 cm(-1)), tunable F-center laser in the Delta upsilon = 1 fundamental manifold with near shot noi se limited detection levels of 10(8) molecules/cm(3)/quantum state per pulse. The high absorption sensitivity, long mean free path lengths, and low-density conditions in the intersection region permit collision -free HF(upsilon, J) rovibrational product state distributions to be e xtracted for the first time. Summed over all rotational levels, the HF vibrational branching ratios are 27.0(5)%, 54.2(23)%, 18.8(32)%, and <2(2)%, respectively, into upsilon(HF) = 3:2:1:0 The nascent vibration al distributions are in good agreement with rotationally unresolved cr ossed-beam studies of Neumark et al. [J. Chem. Phys. 82, 3045 (1985)], as well as with full quantum close-coupled calculations of Castillo a nd Manolopoulos [J. Chem. Phys. 104, 6531 (1996)] on the lowest adiaba tic F+H-2 potential surface of Stark and Werner [J. Chem. Phys. 104, 6 515 (1996)]. At a finer level of quantum state resolution, the nascent rotational distributions match reasonably well with full quantum theo retical predictions, improving on the level of agreement between theor y and experiment from early arrested relaxation studies. Nevertheless, significant discrepancies still exist between the fully quantum state -resolved experiment and theory, especially for the highest energetica lly allowed rotational levels. (C) 1998 American Institute of Physics. [S0021-9606(98)00545-5].