  Cyclic-C3HD (c-C3HD) is a singly deuterated isotopologue of c-C3H2, which is
one of the most abundant and widespread molecules in our Galaxy. We observed
IRAS 16293-2422 in the 3 mm band with a single frequency setup using the EMIR
heterodyne 3 mm receiver of the IRAM 30m telescope. We observed seven lines of
c-C3HD and three lines of c-C3H2. Observed abundances are compared with
astrochemical simulations using the NAUTILUS gas-grain chemical model. Our
results clearly show that c-C3HD can be used as an important supplement for
studying chemistry and physical conditions for cold environments. Assuming that
the size of the protostellar envelope is 3000 AU and same excitation
temperatures for both c-C3H2 and c-C3HD, we obtain a deuterium fraction of
$14_{-3}^{+4}\%$.
