A Comparison of c-C_3H_2 and I-C_3H_2 in the Spiral Arm Clouds

Abstract

Using the IRAM 30-m telescope, we observed molecular absorption lines from c-C_3H_2 produced in diffuse clouds toward the high-mass star forming regions W51 e1/e2 and W49N to determine the abundance ratio between the cyclic and linear isomers of C_3H_2 (N_c/N_l). The abundance ratio is found to be 3-5 in the sources where l-C_3H_2 was previously detected. A possible source of uncertainty in the determination of N_c/N_l is related to the estimate of N(c-C_3H_2). The main goal of this paper is verification of this hypothesis.