Labeling experiment with H2O18 afforded the 18O-labelled
nitrate. In FT-IR spectrum, the nitrate stretching frequency at
1384 cm1 was found to shift at 1320 cm1 (Supporting information).
While the reaction was carried out in presence of 18O2,
incorporation of 18O into the NO3
was not observed. This suggests
the involvement of water in the reaction. The release of H+ was
qualitatively confirmed from the change of pH of the reaction
medium.