Can Cytosine, Uracil, and Thymine Be Formed from HC₃N and H₂NCO⁺ in Interstellar Space?

Syntheses of cytosine, uracil, and thymine starting from interstellar molecules were examined theoretically. Potential energy surfaces for the formation protonated cytosine (CyH+), uracil (UrH+), (ThH+) cyanoacetylene (HC3N), isocyanic acid (H2NCO+), one NH3, H2O, CH3OH, respectively, determined by quantum chemical calculation using CBS-QB3 method. Barrierless pathways found all three reactions. Investigation energetics kinetics further possible reactions CyH+, UrH+, ThH+ led to conclusion that could not be formed along proposed in gas phase, whereas their might on icy grain mantles.