Rate Constants and Product Yields for the C + CH3CHO Reaction at Low Temperatures

Abstract

Reactions involving atomic carbon in its ground electronic state, C(³P), play an important role in astrochemistry due to high C atom abundance levels. Here we performed a kinetic investigation of the reaction between C(³P) and acetaldehyde, CH₃CHO, determining rate constants for this process over the 50–296 K range. Measurements of the formation of atomic hydrogen, H(²S), were also performed to provide insight into product formation. Experiments were conducted using a supersonic flow reactor coupled with pulsed laser photolysis for C atom generation and pulsed laser-induced fluorescence in the vacuum ultraviolet range for the detection of both C(³P) and H(²S) atoms. Quantum chemical calculations of the ground triplet state potential energy surface of C₃H₄O were also performed to provide theoretical support for the measurements. The rate constants were large and temperature independent with an average value of 4.0 × 10^–10 cm³ s^–1. This result is consistent with the theoretical results which predict either very low barriers or none at all on the underlying potential energy surface. Although experimental difficulties prevented the quantitative determination of H atom formation, qualitatively, H atom yields were very low with CH₃CH/C₂H₄ + CO as the major products based on the calculations. The influence of this reaction on interstellar chemistry was tested using a gas-grain model of dense interstellar clouds. These simulations predict that the C(³P) + CH₃CHO reaction decreases gas-phase CH₃CHO abundances by more than an order of magnitude at early and intermediate cloud ages, with a lower influence at typical dense cloud ages.