The soft X-ray absorption spectrum of the allyl free radical

• Published in: Physical chemistry chemical physics : PCCP Vol. 15; no. 4; pp. 131 - 1318
• Main Authors: Alagia, M, Bodo, E, Decleva, P, Falcinelli, S, Ponzi, A, Richter, R, Stranges, S
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 28.01.2013
• Subjects: Absorption spectra; Carbon; Chemistry; Exact sciences and technology; Free radicals; General and physical chemistry; Ionization; Radicals; Soft x-rays; Three dimensional; X-ray photoelectron spectroscopy; Free radical; X ray absorption
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp43466k

The first experimental study of the X-ray absorption spectrum (XAS) of the allyl free radical, CH 2 CHCH 2 , is reported. A supersonic He seeded beam of hyperthermal allyl radicals was crossed by a high resolution synchrotron radiation (SR) in the focus of a 3D ion momentum imaging time-of-flight (TOF) spectrometer to investigate the soft X-ray absorption and fragmentation processes. The XAS, recorded as Total-Ion-Yield (TIY), is dominated by C1s electron excitations from either the central carbon atom, C C , or the two terminal carbon atoms, C T , to the frontier orbitals, the semi-occupied-molecular-orbital (SOMO) and the lowest-unoccupied-molecular-orbital (LUMO). All of the intense features in the XAS could only be assigned with the aid of ab initio spectral simulation at the Multi-Configuration Self-Consistent-Field (MCSCF) level of theory, this level being required because of the multi-reference nature of the core-excited state wavefunctions of the open shell molecule. The ionization energies (IEs) of the singlet and triplet states of the C1s ionized allyl radical (XPS) were also calculated at the MCSCF level. A clean generation of hyperthermal allyl radicals in a seeded supersonic jet, combined with high resolution synchrotron radiation allowed the first measurement of the allyl XAS obtained as total-ion-yield.