Transitions of propynal identified in the ASAI data toward L1527 with an S/N ratio of ≥3. Transition parameters are given in Table B.2. The observational data are shown in black. A simulation of propynal using the derived best fit column density and temperature is shown in red using a noise-weighted average linewidth derived from our Gaussian fits to the individual lines (1.2 km s⁻¹) and simulated at the same resolution and frequency sampling as the observations.