Difference FTIR spectra of the CH₃CH₂CHO/Cl₂/para-H₂ sample illustrating the effect of the sequential 365 nm (60 min) + 2217 nm (90 min) irradiation (a), free sample standing after photolysis for 420 min (b), 365 nm (30 min) photolysis (c), 2217 nm (100 min) photolysis (d), 400 nm (20 min) photolysis (e), 330 nm (20 min) photolysis (f ), 260 nm (20 min) photolysis (g), and 225 nm (20 min) photolysis (h). The absorption features attributed to the cis-CH₃CH₂CHO are marked with “p”. The unassigned absorption features are labeled with question signs.