  For the first time, the OMC-2/3 region was mapped in C2H(1-0), HC3N(10-9) and
HNC(1-0) lines. In general, the emissions from all the three molecular species
reveal an extended filamentary structure. The distribution of C2H cores almost
follows that of the 1300 $\mu$m condensations, which might suggest that C2H is
a good tracer to study the core structure of molecular clouds. The core masses
traced by HNC are rather flat, ranging from 18.8 to 49.5 $M_{\odot}$, while
present a large span for those from C2H, ranging from 6.4 to 36.0 $M_{\odot}$.
The line widths of both HNC and C2H look very similar, and both are wider than
that of HC3N. The line widths of the three lines are all wider than those from
dark clouds, implying that the former is more active than the latter, and has
larger turbulence caused by winds and UV radiation from the surrounding massive
stars.
