showing presence of similar ν(CN) bands (see Figure ). A notable exception is the absence of the 2111 cm -1 band attributed to BTDN 2-and the band at 2080 cm -1 . The absence of the 2080 cm -1 band under high CO2 concentration suggests that it can be attributed to a reduced BTDN species that reacts with low equivalence of CO2. An additional band at 2130 cm -1 is initially formed and decays relatively slowly.