  A recent suggestion that acetamide, \ce{CH3C(O)NH2}, could be readily formed
on water-ice grains by the acid induced addition of water across the \ce{CN}
bond is now shown to be valid. Computational modelling of the reaction between
\ce{R-CN} (R = H, \ce{CH3}) and a cluster of 32 molecules of water and one
\ce{H3O+} proceeds auto-catalytically to form firstly a hydroxy imine
\ce{R-C(OH)=NH} and secondly an amide \ce{R-C(O)NH2}. Quantum mechanical
tunnelling, computed from small-curvature estimates, plays a key role in the
rates of these reactions. This work represents the first credible effort to
show how amides can be formed from abundant substrates, namely nitriles and
water, reacting on a water-ice cluster containing catalytic amounts of hydrons
in the interstellar medium with consequential implications towards the origins
of life.
