H¹³CO⁺ spectra at positions indicated by bold asterisks in the top panel. The positions are chosen to lie along the connection between the UKIDSS near-IR source and the ATLASGAL peak position, with the first spectra at the peak of the GLIMPSE 8 μm emission. From left to right the clumps are G18.93/1, G18.93/m, and G18.93/4. The upper spectra are at positions closer to the ionizing source. Where possible we fitted one, two, or three gaussian components to the spectra. The fitted line widths and peak positions are given in the spectra.