A Comparison of c-C3H2 and l-C3H2 in the Spiral Arm Clouds

International audienceUsing the IRAM 30-m telescope, we observed molecular absorption lines from c-C<SUB>3</SUB>H<SUB>2</SUB> 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<SUB>3</SUB>H<SUB>2</SUB> (N<SUB>c</SUB>/N<SUB>l</SUB>). The abundance ratio is found to be 3-5 in the sources where l-C<SUB>3</SUB>H<SUB>2</SUB> was previously detected. A possible source of uncertainty in the determination of N<SUB>c</SUB>/N<SUB>l</SUB> is related to the estimate of N(c-C<SUB>3</SUB>H<SUB>2</SUB>). The main goal of this paper is verification of this hypothesis