Ab Initio Thermochemistry of the Hydrogenation of Hydrocarbon Radicals Using Silicon-, Germanium-, Tin-, and Lead-Substituted Methane and Isobutane

Abstract

A series of reactions of the type Y‚ + XH 4 f YH + ‚XH 3 and Y′‚ + HX(CH 3 ) 3 f Y′H + ‚X(CH 3 ) 3 , where Y ) H, CH 3 ; Y′ ) CH 3 , C(CH 3 ) 3 ; and X ) Si, Ge, Sn, Pb are studied using state-of-the-art ab initio electronic structure methods. Second-order Møller-Plesset perturbation theory; the coupled-cluster singles, doubles, and perturbative triples method; and density functional theory are used with correlation-consistent basis sets (cc-pVNZ, where N ) D, T, Q) and their pseudopotential analogs (cc-pVNZ-PP) to determine the transitionstate geometries, activation barriers, and thermodynamic properties of these reactions. Trends in the barrier heights as a function of the group IVA atom (Si, Ge, Sn, and Pb) are examined. With respect to kinetics and thermodynamics, the use of a hydrogen attached to a group IVA element as a possible hydrogen donation tool in the mechanosynthesis of diamondoids appears feasible.

Optimal Approach Trajectories for a Hydrogen Donation Tool in Positionally Controlled Diamond Mechanosynthesis

“…+0 16 eV, results that are very consistent with the +0 21 eV barrier and −0 62 eV transfer favorability previously estimated byTemelso et al (2007) 16. …”

“…The first high-quality analysis of the Ge-based HDon tool operating on small cluster targets by Temelso et al 16 reports H donation from a Ge-substituted isobutane model tooltip to an sp 3 carbon monoradical recipient site (isobutane model) to be exoergic by E = −0 62 eV at the CCSD(T)/DZ-PP level of theory with a +0 21 eV reaction barrier calculated at the UMP2/DZ-PP level of theory. Based on bending potentials calculated at the MP2/ccpVDZ[-PP] level of theory, positional uncertainty of the donor H atom is estimated to be < 0 22 Å at 298 K or one-tenth the ∼ 2 5 Å spacing between potential donation sites on an unreconstructed C(111) diamond surface, thus allowing adequate positional control during the donation operation.…”

Meeting the Challenge of Building Diamondoid Medical Nanorobots

“…After an atomically precise structure has been fabricated by a succession of hydrogen abstractions and carbon depositions, the fabricated structure must be passivated to prevent additional unplanned reactions. While the hydrogen abstraction tool is intended to make an inert structure reactive by creating a dangling bond, the hydrogen donation tool (Temelso et al 2007) does the opposite. It makes a reactive structure inert by terminating a dangling bond by adding an H atom.…”

A Minimal Toolset for Positional Diamond Mechanosynthesis

“…Step of the Ge-based HDon tool operating on small cluster targets by Temelso et al 77 reports H donation from a Ge-substituted isobutane model tooltip to an sp 3 carbon monoradical recipient site (isobutane model) to be exoergic by E = −0 62 eV at the CCSD(T)/DZ-PP level of theory with a +0 21 eV reaction barrier (easily overcome by mechanical force; Section 1) calculated at the UMP2/DZ-PP level of theory. Based on bending potentials calculated at the MP2/cc-pVDZ[-PP] level of theory, positional uncertainty of the donor H atom is estimated to be <0 22 Å at 298 K or one-tenth the ∼2 5 Å spacing between potential donation sites on an unreconstructed C(111) diamond surface, thus allowing adequate positional control during the donation operation.…”

“…DCB6X (X = Si, Ge, Sn) is at present the only class of carbon transfer tools that has been computationally validated on a specific diamond surface. 19 20 22 Ge is strongly preferred 20 as the dimer supporting atom in DCB6Ge (H 12 C 9 Ge-C≡C-GeC 9 H 12 ), influencing the selection of Ge over Si/Sn/Pb alternatives for HDon 77 thus minimizing the number of different elements required in the proposed minimal toolset. The DCB6Ge dimer placement or "DimerP" tool ( Fig.…”