H¹³CN(2−1) spectra towards the Seahorse IRDC clumps. Hyperfine structure fits to the lines are overlaid in green. While the velocity range shown in each panel is the same, the intensity range is different to better show the line profiles. The H¹³CN line is seen in absoprtion towards SMM 5 (and a hint of it in SMM 6). The red, vertical dashed line in the SMM 6 panel shows the systemic velocity derived from C¹⁷O(J = 2−1) by Miettinen (2012).