Phosphorus and silicon analogs of isocyanic acid: Microwave detection of HPCO and HNSiO

Phosphaketene, HPCO, and silaisocyanic acid, HNSiO, have been characterized in the gas phase for the first time, employing Fourier transform microwave spectroscopy. Besides the parent isotopic species, the rare isotopologs (HPCO)-C-13, (HNSiO)-Si-29, and (HNSiO)-Si-30 were also observed. The molecular parameters derived experimentally agree very well with results of new quantum-chemical calculations performed at the coupled-cluster level of theory. Other derivatives of HNCO, in which one atom is replaced with its third-row counterpart, or two atoms are replaced with their second-row counterparts, may be detectable using the same combined theoretical/experimental approach. Because both isocyanic acid, HNCO, and its sulfur variant HNCS are abundant in molecule-rich astronomical sources, HPCO and HNSiO are good candidates for future radio astronomical searches. (C) 2015 Elsevier Inc. All rights reserved.