Difference IR spectra obtained after UV irradiation of C₂H₂:NH₃ ice mixtures with ratios of (a) 1:0, (b) 1:0.2, (c) 1:0.5, (d) 1:1.4, and (e) 1:2.7 at 10 K for a fluence of 5.7 × 10¹⁷ photon cm⁻². Infrared spectra are offset for clarity. The shaded area marks the absorption features of the parent species (i.e., blue is for C₂H₂ and red is for NH₃ ) now visible as negative bands.