Fission processes following core level excitation in closo ‐1,2‐orthocarborane

Abstract

Time‐of‐flight mass analysis with multi‐stop coincidence detection was used to study the multi‐cation ionic fragmentation of the closo carborane cage molecule closo ‐1,2‐orthocarborane (C2B10H12) following inner‐shell excitation in or above the B 1s regime. Electron ion coincidence spectra reveal the cationic products which are formed after core level excitation. Distinct changes in fragmentation pattern are observed as a function of excitation energy. Photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopy was used to study the dominant fission routes in the core level excitation regime. Series of ion pairs are identified, where asymmetric fission dominates, leading to ion pairs of different mass. Suitable fission and fragmentation mechanisms are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photofragmentation of the closo-Carboranes Part II: VUV Assisted Dehydrogenation in the closo-Carboranes and Semiconducting B10C2Hx Films

“…The first vertical ionization energies (IE) have now been determined for the first time for two closo-phosphacarboranes: ortho-1,2-PCB 10 It is above these ionization threshold that cation fragmentation occurs, and although multiple fragmentation routes are possible for the closo-carboranes, 18,19 of interest here are the hydrogen loss from the parent cation as occurs at energies near the ionization energies. 18 closo-Carborane Dehydrogenation in the near VUV.…”

“…The structures of the different semiconducting boron carbides, and the relationship between the different polytypes, are not well understood at present, in spite of much successful device fabrication. Some studies of closocarborane decomposition have been undertaken 14,16,18,19 but have not investigated the favored dehydrogenation routes in both the free closo-carboranes and the semiconducting boron carbide films grown from the closo-carboranes.…”

Double Cation Formation from the Photo-Fragmentation of the closo-Carboranes

“…Recently, there has been an effort to understand the ionic and photo fragmentation of the closo-carboranes [1][2][3][4][5]. This work has been fueled, in large measure, by a need to understand the growth and chemistry of the semiconducting boron carbides of approximate stoichiometry "C 2 B 10 H " (where represents up to 40 at.…”

“…There is sufficient photoionization cross-section [1,8,9] and energy for cation pair production [1,3] at the B 1s and C 1s core thresholds. Indeed at or above these thresholds, it has been noted that multiple fragment ion formation was not only possible, but likely, although not a majority fragmentation pathway [1,3].…”

“…There is sufficient photoionization cross-section [1,8,9] and energy for cation pair production [1,3] at the B 1s and C 1s core thresholds. Indeed at or above these thresholds, it has been noted that multiple fragment ion formation was not only possible, but likely, although not a majority fragmentation pathway [1,3]. There is already clear experimental evidence that the photo cation pair production of closo-1,2-orthocarborane does not lead to a statistical fragmentation of the icosahedral C 2 B 10 H 12 cage molecule and that some cation pairs are favored [3].…”