Left: RAIR spectra obtained after the deposition of 10 ML of HCCH ice at 10 K (a, black line), after the exposure of this obtained ice with 4.6 × 10₁₆ cm⁻² photons (b, red line) and by subtracting the initial spectrum (a) from spectrum (b) (green line). Right: RAIR spectra obtained after the UV-exposure of 10 ML thick pure HCCH ice at 10 K with 4.6 × 10¹⁶ cm⁻² photons (a, red line), the consequent exposure of this photoprocessed ice with 1.3 × 10¹⁷ cm⁻² H atoms at 10 K (b, blue line), and by subtracting the initial spectrum (a) from spectrum (b) (green line). The grey dashed and dotted lines are the reference RAIRS spectra obtained for the pure C₄H₂ and C₄H₄ ices by Zhou et al. (2009) and Kim & Kaiser (2009). All spectra are offset for clarity.