Radical-Radical Addition Mechanism Sample Clauses

Radical-Radical Addition Mechanism. In an attempt to model methyl formate grain-surface formation, an astrochemical code in- corporating grain-surface chemistry was presented by Xxxxxx and Xxxxxx (2006). Under this model, radicals on the grain surface begin to dominate the organic chemistry of star- formation during the rising temperature (from 10 K to ∼200 K) of an evolving hot core. This study showed that methyl formate may form on grain surfaces directly from the reac- tion between the highly abundant formyl radical (HCO) and the methoxy radical (CH3O). Intriguingly, glycolaldehyde, a sugar-like molecule of prebiotic interest, may also form directly from the reaction of formyl and another methanol photodissociation product, hy- droxymethyl (CH2OH). An expanded and revised gas/grain chemical network (GWWH08) confirmed the importance of this general model, leading Xxxxxx et al. to hypothesize that methanol photodissociation may strongly govern the relative abundances of these isomers. Yet the extent of the influence of photodissociation on COM chemistry had remained unex- plored. To test this hypothesis, a number of permutations on the branching ratios (BRs) of methanol’s cosmic-ray-induced photodissociation were incorporated into the gas/grain net- work used in GWWH08. Attention was then focused on the affected abundances of methyl formate and its structural isomers during the warm-up phase of the model. Only the BRs for the CR-induced photodissociation of methanol were altered so that direct comparison could be made to previous work. The permutations of the CR-induced photodissociation BRs were tested for the gas-phase and grain surface processes, both individually to test the effects that each phase may contribute, and in combination to characterize the total effects. Branching Ratio Sets The following channels are those considered in the model for the photon- or CR-induced photodissociation of methanol: CH3OH + hν −→ CH3 + OH, (2.1a) −→ CH2OH + H, (2.1b) −→ CH3O + H. (2.1c) The sets of BRs to test, as summarized in Table 2.1, were chosen so that each pho- todissociation channel was emphasized in one of the BRs. This enables the quantification of the extreme limits of the reaction chemistry that may ensue following the evolution of the photodissociation products. The labeling scheme used hereafter is as follows: label = prefix suffix timescale, where the prefixes are: • B (both grain surface and gas phase methanol photodissociation channels); Table 2.1. Branching ratios of Reaction 1.1 u...