CN in dark clouds.

CN (N = 1-0) emission was detected toward six locations in the Taurus dark cloud complex, but was not detected with comparable or better sensitivity toward L183 and B227. The CN hyperfine ratios are near unity toward four directions in Taurus; at these positions, the column density of CN is greater than approximately 6 x 10 to the 13th/sq cm (comparable to that found in many warm molecular clouds). It is noted that CN line emission should be weak from cold dark clouds even if CN column densities are large, because of low excitation (less than approximately 4 K) in all but the densest clouds (nH2 greater than approximately 10,000/cu cm). The relative abundance of CN in TMC-1, like those of the cyanopolyyne molecules, is enhanced by at least a factor of 10 relative to NH3, (C-13)O, and (C-18)O over that in L183.