ATOMIC CARBON IN THE ENVELOPE OF IRC+10216

We report observations of the P-3(1) --> P-3(0) transition of atomic c arbon at 492 GHz in IRC + 10216, made at the Caltech Submillimeter Obs ervatory. The C I emission from the central position of IRC + 10216 wa s found to have a main beam temperature of about 0.4 K and to be doubl y peaked at the expansion velocity of the CO envelope. Its spatial dis tribution can be modeled by two shells of radius approximately 15'' an d 45'' with column densities to the central star in the P-3(1), state of 7 x 10(15) and 4 x 10(15) cm-2, respectively. Based on comparison o f our data with a recent photodissociation and chemical calculation of the abundances in the circumstellar envelope, we suggest that the two shells may be due to photodissociation of acetylene and carbon monoxi de, respectively, but appearing at smaller radii than predicted.