Fig. 4.

FTIR difference spectra of qCu_ANOR–CO. At room temperature (top traces), the ν(CO) are isolated using ¹²CO–¹³CO spectra (blue trace: no chloride added, green trace: 3 M chloride). At 15 K (bottom traces), ‘dark’ minus ‘illuminated’ spectra reveal photosensitive ν(CO) modes (black trace: ¹²CO; red trace: ¹³CO; and green trace: ¹²CO in the presence of 3 M NaCl). A schematic interpretation of the binding of CO in qCu_A NOR is also shown (adapted from ref. 57).