Fundamental Vibrational Frequencies and Spectroscopic Constants of Substituted Cyclopropenylidene (c-C₃HX, X = F, Cl, CN)

The recent detection of ethynyl-functionalized cyclopropenylidene (c-C₃HCâ‚‚H) has initiated the search for other functional forms of cyclopropenylidene (c-C₃Hâ‚‚) in space. There is existing gas-phase rotational spectroscopic data for cyano-cyclopropenylidene (c-C₃HCN), but the present work provides the first anharmonic vibrational spectral data for that molecule, as well as the first full set of both rotational and vibrational spectroscopic data for fluoro- and chloro-cyclopropenylidenes (c-C₃HF and c-C₃HCl). All three molecules have fundamental vibrational frequencies with substantial infrared intensities. Namely, c-C₃HCN has a moderately intense fundamental frequency at 1244.4 cmâ»Â¹, while c-C₃HF has two large intensity modes at 1765.4 and 1125.3 cmâ»Â¹ and c-C₃HCl again has two large intensity modes at 1692.0 and 1062.5 cmâ»Â¹. All of these frequencies are well within the spectral range covered by the high-resolution EXES instrument on NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). Further, all three molecules have dipole moments of around 3.0 D in line with c-C₃Hâ‚‚, enabling them to be observed by pure rotational spectroscopy, as well. Thus, the rovibrational spectral data presented herein should assist with future laboratory studies of functionalized cyclopropenylidenes and may lead to their interstellar or circumstellar detection. ; © 2021 American Chemical Society. Received: July 23, 2021; Revised: September 14, 2021; Published: October 5, 2021. The present work is supported by NASA Grant NNX17AH15G and NSF Grant OIA-1757220. The Mississippi Center for Supercomputing Research (MCSR) graciously provided the computational resources. T.J.L. gratefully acknowledges the financial support from the 17-APRA17-0051, 18-APRA18-0013, and 18-2XRP18_2-0046 NASA grants. D.J.P. would also like to acknowledge support from the Ronald E. McNair Program at the University of Mississippi. The authors declare no competing financial interest. ; Supplemental Material - jp1c06576_si_001.pdf