Measurements of Low Temperature Rate Coefficients for the Reaction of CH with CH2O and Application to Dark Cloud and AGB Stellar Wind Models

Rate coefficients have been measured for the reaction of CH radicals with formaldehyde, CH2O, over thetemperature range of 31–133 K using a pulsed Laval nozzle apparatus combined with pulsed laser photolysis andlaser-induced fluorescence spectroscopy. The rate coefficients are very large and display a distinct decrease withdecreasing temperature below 70 K, although classical collision rate theory fails to reproduce this temperaturedependence. The measured rate coefficients have been parameterized and used as input for astrochemical modelsfor both dark cloud and Asymptotic Giant Branch stellar outflow scenarios. The models predict a distinct change(up to a factor of two) in the abundance of ketene, H2CCO, which is the major expected molecular product of the CH + CH2O reaction.