On the Spectroscopy of Phosphaalkynes: Millimeter- and Submillimeter-Wave Study of C₂H₅CP

Ethyl phosphaethyne, C₂H₅CP, has been characterized spectroscopically in the gas phase for the first time, employing millimeter- and submillimeter-wave spectroscopy in the frequency regime from 75 to 760 GHz. Spectroscopic detection and analysis was guided by high-level quantum-chemical calculations of molecular structures and force fields performed at the coupled-cluster singles and doubles level extended by a perturbative correction for the contribution from triple excitations, CCSD(T), in combination with large basis sets. Besides the parent isotopologue, the three singly substituted ¹³C species were observed in natural abundance up to frequencies as high as 500 GHz. Despite the comparably low astronomical abundance of phosphorus, phosphaalkynes, R–CP, such as C₂H₅CP are promising candidates for future radio astronomical detection.