A new apparatus for gas-phase low temperature kinetics study: Kinetics measurement and product detection of the CH + propene reaction at 23 K.

This article focuses on the development and application of a novel experimental instrument combining laser-induced fluorescence (LIF) and vacuum ultraviolet (VUV) photoionization reflectron time-of-flight mass spectrometry (ReTOFMS) with a pulsed helium Laval nozzle to study low-temperature reaction kinetics of astrochemical relevance. Using this setup, the reaction between the methylidyne radical (CH) and propene (C3H6) was investigated at 23 ± 3 K, yielding a second-order rate coefficient of (3.4 ± 0.6) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ via LIF measurements. VUV ReTOFMS detected the dominant product channel CH + C3H6 → C4H6 + H, consistent with previous room-temperature studies, though isomer-specific identification was not achieved; a less intense mass peak at m/z 53 suggests either dissociative ionization of C4H6 or an alternative product channel C4H5 + H2. Given the presence of CH and propene in cold molecular clouds, these reaction products are likely relevant to interstellar chemistry and should be incorporated into astrochemical models to improve understanding of unsaturated hydrocarbon and polycyclic aromatic hydrocarbon (PAH) formation in cold interstellar environments.