Molecular beams studies of the energetics and dynamics of elementary chemical reactions

Quantum mechanical effects on the angular distribution of HF products from the F + H/sub 2/ reaction were studied using crossed atomic and molecular beams with a rotatable mass spectrometer detector and time-of-flight velocity analysis. Measurement of the singlet-triplet splitting of CH/sub 2/ from the recoil velocities of fragments from ketene photodissociation in a molecular beam is also reported. Partial center-of-mass angular distributions, and velocity flux contour maps have been derived for individual vibrational states of the HF product from the F + H/sub 2/ reaction at collision energies of 2 and 3 kcal/mole. The center-of-mass distributions were obtained by analysis of laboratory angular and time-of-flight measurements of the reactive scattering. The results are consistent with recent three dimensional quantum mechanical scattering calculations, which predict that resonance effects should appear in the product angular distributions in this energy range. The photofragmentation of ketene in a molecular beam was used to measure the singlet-triplet splitting in CH/sub 2/. A rare gas halide excimer laser operating at 351 nm (XeF) and 308 nm (XeCl) dissociated the ketene. Time-of-flight measurements of the fragment velocities allowed determination of the energetics of the dissociation. The /sup 1/A/sub 1/ - /sup 3/B/sub 1/ splitting in CH/sub 2/ was found to be 8.5 +- 0.8 kcal/mole. This agrees with many experimental results, but not with the value of 19.5 kcal/mole derived from recent photodetachment experiments on CH/sub 2//sup -/