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Mechanically stiff mechanosynthetic systems can reliably block many unwanted reactions

In conventional chemistry, molecules move and collide freely, making reaction probabilities sensitive to all possible reactions among molecules in the same neighborhood. Modest errors in calculated energy barriers can result in large errors in relative reaction rates. In a mechanically stiff mechanosynthetic system, however, the sensitivity to such errors can be effectively eliminated by making unwanted collisions effectively impossible. A linear elastic mechanical constraint with a stiffness ks creates an energy barrier to a displacement Δx of ksΔx2/2. For Δx = 0.3 nm (a typical distance between potential reactive sites) and ks = 10 N/m (a moderate stiffness for a nanomechanical system), the barrier is greater than 100kT300 and the mean waiting time for an unwanted collision is far longer than the age of the universe.