Photochemistry of Methane and the Formation of Hydrocyanic Acid (HCN) in the Earth’s Early Atmosphere

The photochemistries of methane and HCN are discussed in the context of the primitive terrestrial atmosphere,using a detailed numerical model. In the absenceof abundant O2, absorption of solar EUV (λ < 1023Å) by N2 provides a large thermosphersic source of atomic nitrogen. Methane is oxidized cleanly and efficiently,provided CO2 is more abundant than CH,•. Otherwise,a large fraction of the methane…