Near-threshold photoionization spectroscopy of the mono-terpene limonene and carvone

The photoionization of two representative mono-terpenes (R-limonene and R-carvone) has been investigated using low energy synchrotron radiation in the region from the threshold for ionization of these molecules up to 11 eV. Data from threshold photoelectron spectra are interpreted with the aid of Outer Valence Green's Function (OVGF) calculations to identify the character of the outermost orbitals and improved ionization potentials are deduced. Fragmentation of the parent ions is studied using threshold photoelectron-photoion coincidence (TPEPICO) time-of-flight (TOF) mass spectrometry and breakdown diagrams identifying the major products in this near-threshold region are presented