Vibrationally excited states of HC5P: millimetre-wave spectroscopy and coupled cluster calculationsElectronic supplementary information (ESI) available: Theoretical force constants, measured transition frequencies and least-squares residuals. See http://www.rsc.org/suppdata/cp/b3/b307069g/

A more efficient method for the production of the unstable HC5P molecule has been found, based on copyrolysis of phosphorus trichloride and cyclopentene. This allowed us to extend the study of the rotational spectrum of HC5P to a large number of vibrationally excited states which approximately lie between 150 and 650 cm−1, namely (v6v7v8v9v10v11) = (000002), (000003), (000010), (000020), (000100), (001000), (010000), (100000), (000011), (000101), and (001001). The anharmonic resonances which couple the (100000) stretching state with the (000020) and (000101) bending states, and the l-type resonances which occur between the different sublevels of a given bending state have been taken into account in the analysis of the spectra, which yielded determinations of the α6, α7, α8, α9, and α10 vibration–rotation coupling constants, and of the xL(11,11), xL(10,10), xL(10,11), xL(9,11), and xL(8,11) anharmonicity constants. The experimental work was assisted by coupled-cluster single double triple [CCSD(T)] calculations, performed using 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.