Fig. 4: The wavelength dependences of O atom quantum yields.
Plot showing (A) the wavelength dependences of the reconstructed VUV solar flux (90–200 nm, the black lines) at ~10 My (10 My = 1 × 107 years, reconstructed from ref. 31. The VUV solar flux at modern period or the interstellar radiation field (ISRF)41 also can be used, which may modify the yield of O-production a little, but the final conclusion holds), the total absorption (σtot, the solid blue curve)32 and photoionization (σion, the dotted blue curve) cross-sections42 of H2O, and (B) the quantum yield for forming O-atom photoproducts (O(3P/1D) + 2H), Γ, determined in the present work (the red dot). It is noted that the predissociation rate of H2O is sufficiently fast that the fluorescence quantum yield must be negligible, so the total photodissociation cross-section will be almost the same as the photoabsorption cross-section. The polynomial function through the latter data is used to derive the reported overall O product quantum yield (the black curve in B). The quantum yields at λ = 111.5, 115.2, 121.57 nm are obtained from refs. 15, 24, 26. The error bars represent the standard deviation (1σ) of three times measurements. Source data are provided as a Source Data file.
