Ultraviolet Photodissociation of the N, N ‑Dimethylformamide Cation

Journal article

N, N-Dimethylformamide (DMF) provides a useful small-molecule model for studying features of the peptide bond that forms the backbone of proteins. We report results from a comprehensive multimass velocity-map imaging study into the ultraviolet (UV) photolysis of the N, N-dimethylformamide cation (DMF+) at wavelengths of 225, 245, and 280 nm. Electronic structure calculations on DMF and DMF+ were employed to help interpret the experimental results. DMF+ ions are generated by 118 nm single-photon ionization of neutral DMF. Subsequent UV photolysis is found to lead to selective cleavage of the N–CO amide bond. This yields HCO + NC2H6 + as major products, with virtually all of the excess energy released into internal modes of the fragments. The data also indicate a small branching ratio into the HCO+ + NC2H6 product pair, which can be accessed from the 32A′ electronic state of DMF+. N–CO bond dissociation can also be accompanied by simultaneous intramolecular hydrogen transfer from the oxygen to the nitrogen end of the amide bond, in which case NCH4 + can be formed efficiently at all three wavelengths. The primary NC2H6 + product is relatively long-lived, but the high degree of internal excitation often results in secondary fragmentation via a variety of pathways to form CH3 +, NH4 +, NCH2 +, and NC2H4 +, with secondary dissociation more likely at higher photon energies. The isotropic velocity-map images recorded for the various fragments attest to the long lifetime of NC2H6 + and also imply that dissociation most probably occurs from the same set of electronic states at all wavelengths studied; these are thought to be the 12A′ ground state and 22A′ first excited state of the DMF+ cation.

Authors: Milešević, D; Butler, A; Robertson, PA; Vallance, C

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: The Journal of Physical Chemistry A
• Volume: 128
• Issue: 49
• Pages: 10525-10533
• Publication date: 2024-12-03
• Acceptance date: 2024-11-26
• DOI: 10.1021/acs.jpca.4c06227
• EISSN: 1520-5215
• ISSN: 1089-5639
• Language: English