An Experimental and Theoretical Investigation of the Gas-Phase C(3P) + N2O Reaction. Low Temperature Rate Constants and Astrochemical Implications

TL;DR

This study combines experimental measurements and theoretical calculations to determine the rate constants of the C(3P) + N2O reaction at low temperatures, revealing its potential impact on astrochemical models of interstellar environments.

Contribution

It provides the first low-temperature rate constants for the C(3P) + N2O reaction and explores its astrochemical implications through combined experimental, theoretical, and modeling approaches.

Findings

Rate constant increases as temperature decreases, reaching 7.9 x 10^-11 cm^3 s^-1 at 50 K.

The reaction significantly reduces N2O abundance in dense interstellar clouds.

Theoretical calculations support experimental data and enable extrapolation to lower temperatures.

Abstract

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.