We report combined studies on the prototypical S(D21)+H2 insertion reaction. Kinetics and crossed-beam experiments are performed in experimental conditions approaching the cold energy regime, yielding absolute rate coefficients down to 5.8~K and relative integral cross sections to collision energies as low as 0.68~meV. They are supported by quantum calculations on a potential energy surface treating long-range interactions accurately. All results are consistent and the excitation function behavior is explained in terms of the cumulative contribution of various partial waves.

The temperature dependences of the methylidyne radical reactions with methane, allene, methylacetylene and propene were studied. This work was carried out in a supersonic flow reactor coupled with pulsed laser photolysis (PLP) and laser-induced fluorescence (LIF) techniques. Three Laval nozzles were designed to provide uniform supersonic expansions of nitrogen at Mach 2 and of argon at Mach 2 and 3 to reach low temperatures, e.g. 170, 128 and 77 K, respectively. CH radicals were produced by PLP of CHBr₃ at 266 nm and probed by LIF. The exponential decays of the CH fluorescence were acquired, hydrocarbons being introduced in excess. The rate constants for the CH + CH₄ reaction are in good agreement with the temperature dependence proposed by Canosa et al. (A. Canosa, I. R. Sims, D. Travers, I. W. M. Smith and B. R. Rowe, Astron. Astrophys., 1997, 323, 644–651, ) i.e. 3.96 × 10⁻⁸ (T/K)^−1.04 exp(−36.1 K/T) in the range 23–298 K. The rate constants of the CH + C₃H₄ (allene), CH + C₃H₄ (methylacetylene) and CH + C₃H₆ (propene) reactions exhibit a small temperature dependence between 77 and 170 K, with a maximum rate around 100 K close to (4.3–4.6) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹.