Probing ultrafast dynamics in photoexcited pyrrole: timescales for 1πσ* mediated H-atom elimination

摘要: The heteroaromatic ultraviolet chromophore pyrrole is found as a subunit in number of important biomolecules: it present heme, the non-protein component hemoglobin, and amino acid tryptophan. To date there have been several experimental studies, both time- frequency-domains, which interrogated excited state dynamics pyrrole. In this work, we specifically aim to unravel any differences H-atom elimination from across an excitation wavelength range 250–200 nm, encompasses: (i) direct (formally electric dipole forbidden) 11πσ* (1A2) state; (ii) initial photoexcitation higher energy 1ππ* (1B2) state. This achieved by using combination ultrafast time-resolved ion yield velocity map imaging techniques gas phase. Following at 250 observe single time-constant 126 ± 28 fs for N–H bond fission. We assign tunnelling out quasi-bound 3s Rydberg surface vertical Franck–Condon region, followed non-adiabatic coupling through 11πσ*/S0 conical intersection pyrrolyl radicals their electronic ground (C4H4N()) together with H-atoms. At 238 to, dissociation along, observed occur 46 22 fs. Upon population 200 rapid → fission process takes place within 52 12 addition cleavage also onset statistical unimolecular vibrationally hot S0 species, formed after relaxation states, 1.0 0.4 ns. Analogous measurements on pyrrole-d1 reveal that these H-atoms are released only C–H cleavage.