Mononuclear Tc and Re carbonyls are the model compounds for the chemical characterization of Bh carbonyls at the single atom chemistry.Our preliminary experiments on the stoichiometry of Re carbonyls in the gas phase deduced that the neutral and the cation species are Re(CO)5 and[Re(CO)6]+,respectively[1].We will report here a theoretical study to confirm their stoichiometry by quantum chemistry calculation.