A NEW MODIFIED-RATE APPROACH FOR GAS-GRAIN CHEMISTRY: COMPARISON WITH A UNIFIED LARGE-SCALE MONTE CARLO SIMULATION

We compare the results of the unified Monte Carlo chemical model with the new modified-rate equation (MRE) method under a wide range of interstellar conditions, using a full gas-grain chemical network. In most of the explored parameter space, the new MRE method reproduces very well the results of the exact approach. Small disagreements between the methods may be remedied by the use of a more complete surface chemistry network, appropriate to the full range of temperatures employed here.