Photodissociation dynamics of N,N-dimethylformamide at 225 nm and 245 nm
Dennis Milesevic, Patrick Robertson, Divya Popat, Claire Vallance Department of Chemistry, Chemistry Research Laboratory, United Kingdom
N,N -dimethylformamide is the simplest tertiary amide and a model compound for investigating the photofragmentation of peptide bonds. [1-7] We report the photodissociation dynamics following excitation at 225 nm and 245 nm using velocity-map imaging. [8-9] Excitation at 225 nm leads to excitation to the 2 1 A'' Rydberg state, following a parallel transition. This state exhibits a barrier along the N-CO "peptide" bond leading to strong correlations between the anistropy parameter β , the product velocities, and the internal energy of the products, as excited molecules try to circumvent the barrier via out-of-plane motions. The oscillator strength between the two lowest lying excited singlet surfaces 1 1 A'' and 2 1 A'' is high as products are formed in their electronic ground-state. Excitation at 245 nm leads to direct population of the two low-lying triplet states viaπ-π * and n-π * transitions to the 1 3 A' and 1 3 A'' states, respectively. The low dissociation barrier of the former leads to high kinetic energy releases following fast dissociation. The high dissociation barrier of the 1 3 A'' state results in lower kinetic energy releases. References 1. N. R. Forde, T. L. Myers, and L. J. Butler, “Chemical reaction dynamics when the Born-Oppenheimer approximation fails: Understanding which changes in the electronic wavefunction might be restricted,” Faraday Discuss. 108, 221–242 (1997). 2. N. R. Forde and L. J. Butler, “Electronic accessibility of dissociation channels in an amide: N,N-dimethylformamide photodissociation at 193 nm,” J. Chem. Phys. 110, 8954–8968 (1999). 3. S. Shin, A. Kurawaki, Y. Hamada, K. Shinya, K. Ohno, A. Tohara, and M. Sato, “Conformational behavior of N-methylformamide in the gas, matrix, and solutionstates as revealed by IR and NMR spectroscopic measurements and by theoretical calculations,” J. Mol. Struct. 791, 30–40 (2006). 4. M. Ruzi and D. T. Anderson, “Photodissociation of N-methylformamide isolated in solid parahydrogen,” J. Chem. Phys. 137, 194313 (2012). 5. X. Qiu, Z. Ding, Y. Xu, Y. Wang, and B. Zhang, “Ultrafast excited-state dynamics in a prototype of the peptide bond: Internal conversion of the isolated N,Ndimethylformamide,” Phys. Rev. A - At. Mol. Opt. Phys. 89, 033405 (2014). 6. P. Salén, V. Yatsyna, L. Schio, R. Feifel, R. Richter, M. Alagia, S. Stranges, and V. Zhaunerchyk, “NEXAFS spectroscopy and site-specific fragmentation of N -methylformamide, N,N -dimethylformamide, and N,N -dimethylacetamide,” J. Chem. Phys. 144, 244310 (2016). 7. M. L. Lipciuc, S. H. Gardiner, T. N. Karsili, J. W. Lee, D. Heathcote, M. N. Ashfold, and C. Vallance, “Photofragmentation dynamics of N,N-dimethylformamide following excitation at 193 nm,” J. Chem. Phys. 147, 013941 (2017). 8. D. W. Chandler and P. L. Houston, “Two-dimensional imaging of state-selected photodissociation products detected by multiphoton ionization,” J. Chem. Phys. 87, 1445–1447 (1987). 9. A. T. Eppink and D. H. Parker, “Velocity map imaging of ions and electrons using electrostatic lenses: Application in photoelectron and photofragment ion imaging of molecular oxygen,” Rev. Sci. Instrum. 68, 3477–3484 (1997).
P14
© The Author(s), 2022
Made with FlippingBook Learn more on our blog