An Experimental and Theoretical Investigation of the Gas-Phase C(3P) +
  N2O Reaction. Low Temperature Rate Constants and Astrochemical Implications
  The reaction between atomic carbon in its ground electronic state, C(3P), and
nitrous oxide, N2O, has been studied below room temperature due to its
potential importance for astrochemistry, with both species considered to be
present at high abundance levels in a range of interstellar environments. On
the experimental side, we measured rate constants for this reaction over the
50-296 K range using a continuous supersonic flow reactor. C(3P) atoms were
generated by the pulsed photolysis of carbon tetrabromide at 266 nm and were
detected by pulsed laser induced fluorescence at 115.8 nm. Additional
measurements allowing the major product channels to be elucidated were also
performed. On the theoretical side, statistical rate theory was used to
calculate low temperature rate constants. These calculations employed the
results of new electronic structure calculations of the 3A" potential energy
surface of CNNO and provided a basis to extrapolate the measured rate constants
to lower temperatures and pressures. The rate constant was found to increase
monotonically as the temperature falls, reaching a value of k(C(3P)+N2O)(50 K)
= (7.9 +- 0.8) x 10-11 cm3 s-1 at 50 K. As current astrochemical models do not
include the C + N2O reaction, we tested the influence of this process on
interstellar N2O and other related species using a gas-grain model of dense
interstellar clouds. These simulations predict that N2O abundances decrease
significantly at intermediate times (10^3 - 10^5 years) when gas-phase C(3P)
abundances are high.
