The reaction F + H2 ? HF + F is a benchmark for comparison between dynamics and kinetics experiments and quantum scattering calculations (1). It is also the primary production route for interstellar HF (2). Recent observations by the Herschel space telescope (3) indicate that HF is an excellent tracer of molecular hydrogen, and provides a sensitive probe of small H2 column density clouds (4, 5). However, the F + H2 reaction possesses a small energetic barrier (~7 kJ mol-1), and around 300 K its rate coefficient falls quite steeply with decreasing temperature. Calculations show, however, that tunnelling plays an increasingly dominant role as the temperature falls. The tunnelling calculations are sensitive not only to the barrier height, but also its precise form, with resonances and non-adiabatic effects playing a strong role (6).We will present experimental measurements of the rate coefficient for the F + H2 reaction between 10 K and 300 K, using the CRESU (Reaction Kinetics in Uniform Supersonic Flow) technique coupled with pulsed laser photochemical kinetics methods. A detailed comparison with quantum reactive scattering calculations on the hybrid LWAL potential surface (6) will also be presented. The experimental measurements necessitated the use of Laval nozzles operating with pure hydrogen buffer gas. The reaction was initiated by pulsed 248 nm photolysis of F2, and followed in real time by pulsed VUV LIF detection of H-atom products at 121.6 nm.References (1) Hu, W. F.; Schatz, G. C. J. Chem. Phys. 2006 , 125, 132301.(2) Neufeld, D. A.; Wolfire, M. G. Astrophys. J. 2009 , 706, 1594-1604.(3) Neufeld, D. A.et al. Astron Astrophys 2010 , 518, L108.(4) Sonnetrucker, P. ; Neufeld, D. et al. Astron.&Astrophys. 2010 , 521, L12.(5) Indriolo, N. et al 2013, Astrophys. J., 2013 , 764, 188.(6) Lique, F.et al. J. Chem. Phys. 2011  , 134.

HF formation from the F(?2?P?J?) + H?2? reaction at very low temperatures

247th National Meeting (2014)

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