Infrared spectra of C₄H₂ films obtained at JPL and PIIM independently. (a) IR spectrum of C₄H₂ ice deposited at 70 K at JPL on a sapphire window. The splitting of the v₅ band is due to the crystalline nature of the ice film. The spectrum is cropped at 2340 cm⁻¹ to remove the absorption band due to gas-phase CO₂ in the path of the IR beam outside the vacuum chamber. (b) IR spectrum of C₄H₂ ice deposited at 70 K at PIIM on a copper substrate.