Carbon Isotope Fractionation in Protoplanetary Disks

We investigate the gas-phase and grain-surface chemistry in the inner 30 AU of a typical protoplanetary disk (PPD) using a new model which calculates the gas temperature by solving the gas heating and cooling balance and which has an improved treatment of the UV radiation field. We discuss inner-disk chemistry in general, obtaining excellent agreement with recent observations which have probed the material in the inner regions of PPDs. We also apply our model to study the isotopic fractionation of carbon. Results show that the fractionation ratio, ¹²C/¹³C, of the system varies with radius and height in the disk. Different behavior is seen in the fractionation of different species. We compare our results with ¹²C/¹³C ratios in the solar system comets, and find a stark contrast, indicative of reprocessing.