Sa. Nizkorodov et al., State-to-state reaction dynamics in crossed supersonic jets: threshold evidence for non-adiabatic channels in F+H-2, FARADAY DIS, (113), 1999, pp. 107-117
The reaction of F+n-H-2 to form HF(v,J)+H is studied in a crossed jet appar
atus under single collision conditions, using high-resolution direct absorp
tion spectroscopy to probe the nascent rotational HF distributions. The J-d
ependent reactive cross-sections into HF(v=3,J) are investigated over a ran
ge of center-of-mass collision energies well below the 1.9 kcal mol(-1) bar
rier for adiabatic chemical reactions with ground state F(P-2(3/2)) atoms.
The energy dependent reaction cross-sections decrease much more slowly with
E-com than predicted by exact quantum calculations on the adiabatic F(P-2(
3/2))+H-2 surface (K. Stark and H. Werner, J. Chem. Phys., 1996, 104, 6515)
. In addition, product states in the HF(v=3) manifold are observed that are
energetically accessible only to the excited spin-orbit state F*(P-1/2)+H-
2(j=0,1) channel. These observations strongly suggest that non-adiabatic re
actions with spin-orbit excited F-*(P-1/2) contribute significantly in the
near threshold region, in good agreement with recent calculations by M. Ale
xander, H. Werner and D. Manolopoulos (J. Chem. Phys., 1998, 109, 5710). Fi
nally, the feasibility of high-resolution IR laser Dopplerimetry on the nas
cent products is illustrated on collision free HF(v,J) distributions formed
from reactions of F+CH4.