CHEMICAL-MODELS OF INTERSTELLAR GAS GRAIN PROCESSES .2. THE EFFECT OF GRAIN-CATALYZED METHANE ON GAS-PHASE EVOLUTION

We have studied the effects upon gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces. We find significant and sustained enhancements in the abundances of several complex hydrocarbon molecules in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. We are thus unable to determine from the models whether or not the grain surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.