The primary photo-dissociation dynamics of aqueous formamide and dimethylformamide

Abstract

We study the primary dissociation dynamics of aqueous formamide (HCONH₂) and dimethylformamide (HCON(CH₃)₂) induced by photo-excitation at λ = 200 nm. The photolysis is recorded with sub-picosecond time resolution by UV pump–IR probe transient absorption spectroscopy. Formamide dissociates with a quantum yield of Φ(t = 20 ps) = 0.30 ± 0.05, t = 20 ps after the excitation. The rest of the excited formamide molecules return to the ground state within t = 1 ps and vibrationally relax towards equilibrium in t ≈ 10 ps. The only product observed is NH₃. NH₃ is produced with a yield of Φ(NH₃) = 0.23 ± 0.10 on a timescale of τ = 3 ± 1 ps and likely constitutes the dominating product. The CO counter product to NH₃ is not observed. Dimethylformamide is photolysed with a quantum yield of Φ(t = 30 ps) = 0.29 ± 0.05, t = 30 ps after the excitation. The photolysis of dimethylformamide produces CO on a time scale of τ ≈ 30 ps. The data indicate that dimethylamine and the N(CH₃)₂ radical are likely photoproducts.