Transitions of propynethial used to calculate the upper limits given in Table 6. In each panel, the red trace shows the transition simulated using the derived upper-limit column density and the physical parameters assumed for that source. The frequency of the transition is given in the top right of each panel, and the quantum numbers for each transition in the top left. The source name is given above each panel. Due to the large variances between observations, the intensity and velocity axes are not uniform between each panel.