  Quantum chemical cluster calculations show that reactions of C$^+$ with HCN
or HNC embedded in the surface of an icy grain mantle can account for the
formation of a recently detected molecule, glycolonitrile, which is considered
to be an important precursor to ribonucleic compounds. Reactions of cations
deposited on ice mantles with minimal kinetic energy have been found
theoretically to result in previously unknown pathways to significant organic
compounds in protostellar systems and the interstellar medium. In density
functional theory cluster calculations involving up to 24H$_2$O, C$^+$ reacts
consistently with HCN embedded in ice to yield the neutral HOCHNC radical with
no barrier, along with H$_3$O+ as a byproduct. If HOCHNC then reacts with H,
three species can be formed: HOCH$_2$CN (isocyanomethanol), HOCH$_2$CN
(glycolonitrile), and HOCHNCH. For the C$^+$ + HNC reaction on ice, the HOCHCN
and H$_2$OCCN radicals form as intermediates, the first of which is another
direct precursor to glycolonitrile via H addition. In addition to
characterizing reaction pathways, predictions are provided of the vibrational
and electronic spectra of the HCN and HNC starting clusters and the HOCHNC
ice-bound intermediate.
