Electron Impact Dissociation of CH2+ Producing CH+ and C+ Fragments

Absolute total cross sections have been separately measured for electron-impact dissociation of CH$_{2}^{+}$ molecular ions resulting in CH$^{+}$ and C$^{+}$ fragments for 3-100 eV collisions using a crossed electron-ion beams technique. Magnetic analysis was used to selectively separate and detect the product CH$^{+}$ and C$^{+}$ ions, which were generated through a combination of dissociative excitation (DE) and dissociative ionization (DI) channels. DE yields neutral light fragments, while DI yields charged light fragments in addition to the CH$^{+}$ or C$^{+}$. In these measurements coincident light H, H$_{2}$ and/or H$^{+}$, H$_{2}^{+}$ fragments were not detected. The relatively `hot' (internal state) 10 keV CH$_{2}^{+}$ ions were provided by the ORNL CAPRICE ECR ion source. For both CH$^{+}$ and C$^{+}$ the measured total cross sections above 20 eV are approximately equal and energy independent at $\sim $ 5 x 10$^{-17}$ cm$^{2}$. The total uncertainties of the present results are about 10{\%} at 40 eV. A broad peaked structure is observed in the CH$^{+}$ cross section rising to $\sim $ 1 x 10$^{-16}$ cm$^{2}$ at 10 eV. These heavy fragment data are being combined with previous measurements of light fragments from dissociation of CH$_{2}^{+}$ in an attempt to develop a coherent picture of the total electron-impact dissociation process. Research was sponsored by the OBES and OFES, U.S. DOE, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.