The conjugate base formed by this protonation reaction is expected to form bicarbonate and carbonate species with ν(CO) bands in the 1750 cm -1 to 1550 cm -1 region. Comparison of ν(CO) bands observed in SEC experiments with reference spectrum of chemically generated bicarbonate and carbonate species under similar conditions (Figure ) suggests additional carbonyl species derived from reaction between CO2 and reduced BTDN are formed.