Spectra of HC¹⁵N, HN¹³C, H¹⁵NC, and H¹³CN observed with IRAM 30 m towards IRDC H. The red line indicates the best Gaussian fit. The hyperfine components of H¹³CN were initially fitted but given the bad results of the fit, in a second step only the main F = 2 → 1 component of H¹³CN was fitted with a single-Gaussian component profile (see red line in bottom panels and Sect. 3.1 for details).