  Atomic carbon in its ground electronic state, C(3P), is expected to be
present at high abundances during the evolution of dense molecular clouds.
Consequently, its reactions with other interstellar species could have a strong
influence on the chemical composition of these regions. Here, we report the
results of an investigation of the reaction between C(3P) and dimethylether,
CH3OCH3, which was recently detected in dark cloud TMC-1. Experiments were
performed to study the kinetics of this reaction using a continuous supersonic
flow reactor employing pulsed laser photolysis and pulsed laser induced
fluorescence for atomic radical generation and detection respectively. Rate
constants for this process were measured between 50 K and 296 K, while
additional measurements of the product atomic hydrogen yields were also
performed over the 75-296 K range. To better understand the experimental
results, statistical rate theory was used to calculate rate constants over the
same temperature range and to provide insight on the major product channels.
These simulations, based on quantum chemical calculations of the ground triplet
state of the C3H6O molecule, allowed us to obtain the most important features
of the underlying potential energy surface. The measured rate constant
increases as the temperature falls, reaching a value of k_(C+CH_3 OCH_3 )= 7.5
x 10-11 cm3 s-1 at 50 K, while the low measured H-atom yields support the
theoretical prediction that the major reaction products are CH3 + CH3 + CO. The
effects of this reaction on the abundances of interstellar CH3OCH3 and related
species were tested using a gas-grain dense cloud model, employing an
expression for the rate constant, k(T) = alpha(T/300)^beta, with alpha = 1.27 x
10-11 and beta = -1.01. These simulations predict that the C(3P) + CH3OCH3
reaction decreases gas-phase CH3OCH3 abundances by more than an order of
magnitude at early times.
