Measurements of Low Temperature Rate Coefficients for the Reaction of CH with CH$_{2}$O and Application to Dark Cloud and AGB Stellar Wind Models

TL;DR

This study measures the reaction rate of CH radicals with formaldehyde at very low temperatures, revealing a decrease in rate below 70 K and impacting astrochemical models of dark clouds and stellar winds.

Contribution

First low-temperature measurements of CH + CH$_{2}$O reaction rates, showing temperature dependence and informing astrochemical models.

Findings

Rate coefficients decrease below 70 K.

Models predict up to twofold change in ketene abundance.

Classical collision theory does not match observed temperature dependence.

Abstract

Rate coefficients have been measured for the reaction of CH radicals with formaldehyde, CH$_{2}$O, over the temperature range 31 - 133 K using a pulsed Laval nozzle apparatus combined with pulsed laser photolysis and laser induced fluorescence spectroscopy. The rate coefficients are very large and display a distinct decrease with decreasing temperature below 70 K, although classical collision rate theory fails to reproduce this temperature dependence. The measured rate coefficients have been parameterized and used as input for astrochemical models for both dark cloud and AGB stellar outflow scenarios. The models predict a distinct change (up to a factor of two) in the abundance of ketene, H$_{2}$CCO, which is the major expected molecular product of the CH + CH$_{2}$O reaction.