ADVANCING THE SEARCH FOR CYCLOPROPENYLIDENECARBENE, THE EXOCYCLIC RING ISOMER OF DIACETYLENE

Ab initio molecular electronic structure theory is used to determine the structure, harmonic vibrational frequencies, infrared (IR) intensities, rotational constants, and dipole moment of cyclopropenylidenecarbene (:C=CC2H2). These properties are investigated using double-zeta plus polarization (DZP) and triple-zeta plus double polarization function (TZ2P) basis sets at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), and coupled cluster with single and double substitutions (CCSD) levels of theory. Based on the IR intensity profile and the large dipole moment (approximately 5 D), we predict that this molecule is a good candidate for an astronomical search and for identification in the laboratory.