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

We have developed a novel instrument to study reaction kinetics of astrochemical interest at low temperatures. This setup integrates laser-induced fluorescence (LIF) and vacuum ultraviolet (VUV) photoionization reflectron time-of-flight mass spectrometry (ReTOFMS) with a supersonic uniform low-temperature flow. A pulsed helium Laval nozzle with a Mach number of 6 was employed, achieving a temperature of 23 ± 3 K and a density of (2.0 ± 0.4) × 1016 molecule cm-3. The second-order rate coefficient for the reaction between the methylidyne radical (CH) and propene (C3H6) at 23(3) K was determined to be (3.4 ± 0.6) × 10-10 cm3 molecule-1 s-1 using LIF kinetics measurements. VUV (118.27 nm) photoionization ReTOFMS detected a dominant product channel, CH + C3H6 → C4H6 + H, without isomer identification. Another less intense mass peak at m/z 53 was also observed, which could either result from the dissociative ionization of the energized C4H6 primary products or indicate another product channel, C4H5 + H2. Given the presence of CH and C3H6 in cold molecular clouds (e.g., TMC-1, Lupus-1a, L1495B, L1521F, and Serpens South 1a), it is predicted that these products can exist in low-temperature interstellar environments.