PHOSPHORUS CHEMISTRY IN THE SHOCKED REGION L1157 B1

We study the evolution of phosphorus-bearing species in one-dimensional C-shock models. We find that the abundances of P-bearing species depend sensitively on the elemental abundance of P in the gas phase and on the abundance of N atoms in the pre-shock gas. The observed abundance of PN and the non-detection of PO toward L1157 B1 are reproduced in C-shock models with shock velocity v = 20 km s(-1) and pre-shock density n(H-2) = 10(4)-10(5) cm(-3), if the elemental abundance of P in the gas phase is similar to 10(-9) and the N-atom abundance is n(N)/n(H) similar to 10(-5) in the pre-shock gas. We also find that P-chemistry is sensitive to O- and N-chemistry because N atoms are destroyed mainly by OH and NO. We identify the reactions of O-bearing and N-bearing species that significantly affect P-chemistry.