Infrared spectra of the studied interstellar ice analogs. Upper: IR spectra obtained after UV irradiation of the C₂H₂ :NH₃ (1:1.4) ice mixture at 10 K for a fluence of 5.7 × 10¹⁷ photon cm⁻². The column densities of C₂H₂ and NH₃ in the ice mixture are 8.1 × 10¹⁶ and 1.1 × 10⁻¹⁷ molecule cm⁻², respectively. Bottom: infrared spectra obtained after UV irradiation of pure ice NH₃ and C₂H₂ at 10 K for a fluence of 5.7 × 10¹⁷ photon cm⁻² and offset for clarity. The column densities of pure C₂H₂ and NH₃ ice are 7.3 × 10⁻¹⁷ and 1.1 × 10⁻¹⁷ molecule cm⁻², respectively. The shaded area is present for the IR spectra before UV irradiation. The IR peaks of the newly formed products are labeled with an arrow.