  Rate constants have been measured for the C(3P) + CH3CN reaction between 50 K
and 296 K using a continuous-flow supersonic reactor. C(3P) atoms were created
by the in-situ pulsed laser photolysis of CBr4 at 266 nm, while the kinetics of
C(3P) atom loss were followed by direct vacuum ultra-violet laser induced
fluorescence at 115.8 nm. Secondary measurements of product H(2S) atom
formation were also made, allowing absolute H-atom yields to be obtained by
comparison with those obtained for the C(3P) + C2H4 reference reaction. In
parallel, quantum chemical calculations were performed to obtain the various
complexes, adducts and transition states relevant to the title reaction over
the triplet potential energy surface, allowing us to better understand the
preferred reaction pathways. The reaction is seen to be very fast, with
measured rate constants in the range (3-4) x 10-10 cm3 s-1 with little or no
observed temperature dependence. As the C + CH3CN reaction is not considered in
current astrochemical networks, we test its influence on interstellar methyl
cyanide abundances using a gas-grain dense interstellar cloud model. Its
inclusion leads to predicted CH3CN abundances that are significantly lower than
the observed ones.
