Theoretical studies of a hydrogen abstraction tool for nanotechnology

Processes that use mechanical positioning of reactive species to control chemical reactions by either providing activation energy or selecting between alternative reaction pathways will allow us to construct a wide range of complex molecular structures. An example of such a process is the abstraction of hydrogen from diamond surfaces by a radical species attached to a mechanical positioning device for synthesis of atomically precise diamond-like structures. In the design of a nanoscale, site-specific hydrogen abstraction tool, we suggest the use of an alkynyl radical tip. Using ab iniiio quantum-chemistry techniques including electron correlation we model the abstraction of hydrogen from dihydrogen, methane, acetylene. benzene and isobutane by the acetylene radical. Of these systems. isobutane serves as a good model of the diamond (1 1 1 ) surface. By conservative estimates, the abstraction barrier is small (less than 7.7 kcal mol-?) in all cases except for acetylene and zero in the case of isobutane. Thermal vibrations at room temperature should be sufficient to supply the small activation energy. Several methods of creating the radical in a controlled vacuum setting should be feasible. Thermal, mechanical, optical and chemical energy sources could all be used either to activate a precursor, which could be used once and thrown away, or alternatively to remove the hydrogen from the tip, thus refreshing the abstraction tool for a second use. We show how nanofabrication processes can be accurately and inexpensively designed in a computational framework.