Angular dependence for v',j'-resolved states in F+H-2->HF(v',j')+H reactive scattering using a new atomic fluorine beam source

Angular distributions are measured for individually resolved nu',j' states of HF produced by F + H-2 --> HF(nu' = 1, j') + H and F + H-2 --> HF(nu'=2,j') + H reactive collisions in a crossed-beams scattering apparatus. Simultaneous resolution of the HF vibrational and rotational states is achieved spectroscopically for the first time, using laser excitation in conjunction with bolometric detection. The technique is sensitive to population differences between nu' = 1,j' and nu' = 2,j' - 1 states optically coupled by specific P-2(j') lines of a vib-rotational chemical laser. The measurements are greatly facilitated by the development of a new high-temperature atomic fluorine beam source, which exhibits excellent stability, very high intensity, and narrow velocity distributions. Features common to individual product rotational states are as follows: strong backward scattering into nu' = 2,j'; weaker backward scattering into nu' = 1,j'; and heretofore unobserved scattering into nu' = 1,j' in the forward hemisphere. These angular distributions agree qualitatively with predictions from fully three-dimensional exact quantum reactive scattering calculations (Castillo et al., J. Chem. Phys. 1996, 104, 6531) that were conducted on an accurate potential energy surface (Stark and Werner, J. Chem. Phys. 1996, 104, 6515). However, quasi-classical calculations conducted on the same potential energy surface do not produce any substantial forward-scattered HF in nu' = 1 (Aoiz et al., Chem. Phys. Lett. 1994, 223, 215), suggesting that its appearance in the forward hemisphere may be a quantum effect. The quantum theoretical cross-sections also suggest that the forward nu' = 1 products arise almost entirely from H-2 reactants initially in j = 1.