Photo-fragmentation of the closo-carboranes

Single and multi-cation ionic fragmentation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C$_{2}$B$_{10}$H$_{12})$] following B 1s and C 1s excitation were studied by time of flight mass analysis. The energetic cycles were constructed to gain some insights into some of decomposition processes. CH$^{+}$ or BH$_{2}^{+}$ fragment dominates the single ion fragmentation of the closo-carboranes. Double ion fragmentation yields and charge separation mass spectra of all three isomers are generally quite similar in that H$^{+}$ and BH$_{2}^{+}$/CH$^{+}$ ion pairs, BH$_{2}^{+}$/CH$^{+}$ and Y$_{11}^{+ }$ion pairs (where Y = (BH) or (CH)), Y$_{3}^{+}$ and Y$_{9}^{+ }$ion pairs (where Y = (BH) or (CH)) yields dominate. The H$^{+}$ and BH$_{2}^{+}$/CH$^{+}$ ion pairs dominate at the B 1s threshold for ortho- and metacarborane, while Y$_{1}^{+}$ and Y$_{11}^{+ }$ion pairs (where Y = (BH) or (CH)) dominates the multi-photofragment ion yield of paracarborane at the B1s threshold.