Laboratory Investigation of Astronomical Reactive Species: the Vibrational Satellites of c-C3H2 Re-Visited

Cyclopropenylidene (c-C₃H₂) is one of the few polyatomic hydrocarbons ubiquitous in our galaxy, despite its reactive carbene nature (see e.g. [1]). Because it is so widely distributed in space, and because its ¹³C, D, and D₂ isotopologues have also been detected (see e.g. [2]), c-C₃H₂ is an ideal probe of the physical conditions in various astrophysical objects. It is surprising though that its vibrational satellites have yet to be detected in the interstellar medium. To enable the interstellar detection of vibrationally excited c-C3H2, and observe for the first time the elusive ν4 and ν9 vibrational modes, we have undertaken an extensive investigation of its spectrum from the centimeter to the submillimeter wavelengths, resulting in the observation of many new vibrational satellites in a promising spectral region for astronomical observations. Our measurements are supported by anharmonic rovibrational calculations using a high-quality ab initio potential energy surface, with particular attention paid to the ν4/ν9 Coriolis interaction.