3-Hydroxypropenal transitions

Local thermodynamic equilibrium (LTE) models were carried out and compared to the observations to constrain the excitation temperature. Additional transitions were searched for in other ALMA archival data of the same source to confirm the presence of 3-hydroxypropenal. More than 7500 different spectral lines, corresponding to more than 11500 transitions, were assigned in the course of our investigation with quantum numbers 2<=J<=100, Ka<=59, and Kc<=97, resulting in a greatly improved set of spectroscopic parameters.

The comparison between the LTE models and the observations yields an excitation temperature of 125K with a column density N=1.0x10^15^cm^-2^ for this species. We identified seven additional lines of 3-hydroxypropenal that show a good agreement with the model in the ALMA archive data. The calculated rotation-tunneling spectrum of 3-hydroxypropenal has sufficient accuracy for radio astronomical searches.

With the solution of the excitation temperature conundrum and the detection of seven more lines, we consider the detection of 3-hydroxypropenal toward IRAS 16293-2422 as secure.