Vibrationally excited states of NC4P: millimetre-wave spectroscopy and coupled cluster calculations

Abstract

A fairly efficient method for the production of the unstable NC₄P molecule has been found, based on copyrolysis of phosphorus trichloride and cyclopropyl cyanide. This allowed us to extend the study of the rotational spectrum of NC₄P to a large number of vibrationally excited states lying between 450 and 750 cm⁻¹, namely (v₅v₆v₇v₈v₉) = (00100), (01000), (10000), (00020), (00101), (01001), (00110), and (01010). The strong Fermi resonance which couples the v₅ = 1 and v₈ = 2 states and the l-type resonances between the different sublevels of the bending states have been taken into account in the analysis of the spectra. The identification of new excited-state spectra was facilitated by CCSD(T) calculations with the cc-pVQZ basis, which provided accurate predictions for a variety of spectroscopic constants, including harmonic vibrational wavenumbers, vibration–rotation coupling constants and l-type doubling constants. Accurate theoretical predictions for the equilibrium structure and the electric dipole moment of NC₄P are also presented.