Steady-state abundances of several nitrogen-bearing and nitrogen-chemistry related species, as a function of the gas-phase elemental abundance ratio of C/O, for three different values of gas-phase elemental abundance of sulphur (from left to right: [S]_tot = 8.0 × 10^-8, 8.0   ×   10^-7, 8.0   ×   10^-6). C/O values include 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, and 0.67, which was the ratio employed in the previous studies of Flower et al. 2006. Top panels: molecules involved in the atomic-to-molecular conversion of nitrogen. Bottom panels: nitrogen hydrides.