Astrochemical Modeling

Previous astrochemical models could not explain the observed abundances of many complex organic molecules (COMs). Tradionally, gas-phase ion-molecule chemistry was employed to explain the observed chemical complexity in hot core regions. However, recnetly these gas-phase mechanisms were found to be inefficient for production of species such as methyl formate.

An alternate to gas-phase chemistry is formation of complex molecules in ices on interstellar dust grains. Absorption spectroscopy on interstellar ices has shown the presence of species like water, methanol, formaldehyde, and formic acid. It is possible that more complex molecules are formed in these ices and then liberated into the gas phase during via thermal evaporation during the formation of a new star. Such chemistry would require a gradual warm-up of the gas and dust around the new star, rather than the previously-assumed jump model:

Radical-radical reactions involving the simple products of ice photolysis had been considered in the past, but had never been included in astrochemical models for hot cores. In a collaboration wih Professor Eric Herbst's group at The Ohio State University (now at UVA), we have now shown that such reactions can lead to the formation of most of the organic molecules observed in hot cores.

In the plot above, the final fractional abundances for a variety of COMs are shown. The standard OSU gas/grain network is that which was used in Garrod et al. (2008) and the modified network containing an additional gas-phase formation route for methyl formate is from Laas et al. 2011. In the plot below, the evolving warm-up phase of a hot core is reflected in the changing relative abundances of complex organics.