Observed H¹³CN and HCNH⁺ spectra (all with a common circular beam of 1.″6) of the nine GMCs indicated in Fig. 1 and Table 1. H¹³CN (1−0), HCNH⁺ (2−1), HCNH⁺ (3−2), HCNH⁺ (4−3), and HCNH⁺ (5−4) are indicated by black, red, green, blue, and purple lines, respectively. The fits to the HCNH⁺ spectra are indicated by black dotted lines. H¹³CN (1−0) spectra are scaled by a factor of 0.1 for better visualization. In each panel, the systemic LSR velocity is indicated by the vertical black dashed line. The potentially blended lines are marked by short vertical lines in the corresponding panels, with the associated species labeled in the central panel for GMC5.