Application of photoelectron spectroscopy to molecular properties. Part 34. Phosphaethene. Synthesis by vacuum gas-solid reaction (VGSR) and characterization by photoelectron spectroscopy

Phosphaethene, the unstable parent compound in the phosphaalkenes series, has been thoroughly investigated using theoretical calculations. For the first time, its electronic structure is evidenced from its photoelectron spectrum. The PE spectra of phosphaethene and 1-phosphapropene, generated in the gas phase by the respective vacuum dehydrochlorination of chloromethylphosphine and 1-chloroethylphosphine, have been recorded in situ by the use of a vacuum device directly coupled to the spectrophotometer. The vertical πP=C and np ionization energies are observed respectively at 10.30 and 10.70 eV for phosphaethene and at 9.75 and 10.35 eV for 1-phosphapropene. The band's characterizations are discussed through correlations with the corresponding imines and with substituted phosphaalkenes and are confirmed by ab initio theoretical calculations. The results indicate a rather significant energetic separation between the two first πP=C and np ionic states.