HOW COMPLETE ARE ASTROPHYSICAL CATALOGS FOR THE MILLIMETER AND SUBMILLIMETER SPECTRAL REGION?

With the growth in sensitivity and angular resolution of millimeter and submillimeter telescopes, the number of unidentified molecular spectral lines in surveys of the interstellar medium has grown rapidly. While some of these unidentified lines are due to as yet unidentified astrophysical species, it is the general consensus that most are due to lines from a limited number of well-known interstellar species, the interstellar weeds. These unidentified lines do not appear in astrophysical line catalogs, which are based on quantum mechanical models and are incomplete primarily because of the difficulty of performing the usual bootstrap assignment and analysis process in their often highly perturbed low-lying vibrational states. To address this problem, we have proposed and demonstrated an alternative catalog approach that is based on the analysis of intensity-calibrated spectra taken over a range of temperatures in the laboratory. These analyses also make it possible to quantitatively address the astrophysical completeness of existing catalogs. In this Letter, we use extensive new experimental data in the 210-270 GHz window to address this question for eight molecules that are considered to be the leading candidates for astronomical weeds-methyl formate, methanol, dimethyl ether, acetaldehyde, sulfur dioxide, methyl cyanide, vinyl cyanide, and ethyl cyanide. Additionally, for each of the eight molecules, we use these results and knowledge of the molecular vibrational/torsional energy levels to predict completeness as a function of astronomical source temperature.