Historically, searches for new astronomical molecules resulted in the detection of favorable, high line strength transitions based on a thermal approximation to the excitation of these species in interstellar environments. Given the temperatures of hot molecular cores inside molecular clouds, these transitions often reside at (sub)millimeter wavelengths. However, line confusion in these wavelength regimes can lead to ambiguous identifications. In addition, line intensities of the anticipated low abundance of large organic molecules may never rise above the noise floor or the confusion limit. The success of molecule searches at centimeter wavelengths has shown that unique excitation conditions can lead to the unambiguous identification of very low abundance species with very high accuracy. In this work, we have identified carbodiimide (HNCNH), which is an isomer of the well-known interstellar species cyanamide (NH2CN), in maser emission using data from the GBT PRIMOS survey toward SgrB2(N). All spectral lines observed are in emission and have energy levels in excess of 170 K, indicating that the molecule must originate in relatively hot gas that characterizes the denser regions of this star forming region and also supporting the evidence that HNCNH is not only a new interstellar molecule but also a new astronomical maser. The anticipated abundance of this molecule from ice mantle experiments is ~10% of the abundance of NH2CN, which is well below the detection limit of any current astronomical facility and, as such, could only be detected by those transitions which are amplified by maser activity.
Citation: Astrophysical Journal
Pub Type: Journals
carbodiimide, interstellar molecule, maser, molecular cloud, radioastronomy, rotational transitions