Rate constants and product yields for the C + CH3CHO reaction at low temperatures

TL;DR

This study investigates the reaction between atomic carbon and acetaldehyde at low temperatures, combining experimental kinetic measurements, quantum chemical calculations, and astrochemical modeling to understand its role in interstellar chemistry.

Contribution

It provides the first temperature-independent rate constants for C(3P) + CH3CHO and assesses their impact on interstellar acetaldehyde abundance through combined experimental and theoretical approaches.

Findings

Rate constants are large and temperature independent (~4.0 x 10^-10 cm^3 s^-1).

H-atom formation yields are very low, with major products being CH3CH and C2H4 + CO.

The reaction significantly reduces gas-phase CH3CHO in dense interstellar clouds.

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 x 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.