Abstract: An electrosprayed water/methanol of Guanosine and Cu(NO₃)₂ was observed to give rise to gas-phase guanine radical ion. The Collision-Induced Dissociation (CID) of guanine radical cation generates five competing dissociation channels to lose NH₃, HCN, CN₂H, H₂NCN and HNCO, respectively. At the same time, the DFT theory was also used to simulate the HCN lost channel. It was turned out that through the three complicated structure changes a 4. 1. 0 bicyclic ion intermediate was formed before kicking off the HCN.