Normalized FTIR spectra of CaCO₃ at 50, 100, and 120 K, before and after 6 hr of irradiation with 10 keV electrons at 4244 nA cm⁻² (high flux) and 1415 nA cm⁻² (low flux). Spectra are largely unchanged upon irradiation except near 4.26 μm, where a characteristic CO₂ ν₃ absorption doublet emerges. Weakening of the 3 μm feature indicates dehydration.