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 1300μm 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 ？at, ranging from 18.8 to 49.5 M , while also presenting a large span for those from C2H, ranging from 6.4 to 36.0 M . 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.
