The Library
Probing ultrafast dynamics in photoexcited pyrrole: timescales for 1πσ* mediated H-atom elimination
Tools
Roberts, Gareth M., Williams, Craig A., Yu, Hui, Chatterley, Adam S., Young, Jamie D., Ullrich, Susanne and Stavros, Vasilios G. (2013) Probing ultrafast dynamics in photoexcited pyrrole: timescales for 1πσ* mediated H-atom elimination. Faraday Discussions, Volume 163 . pp. 95-116. doi:10.1039/c2fd20140b ISSN 0301-7249.
Research output not available from this repository.
Request-a-Copy directly from author or use local Library Get it For Me service.
Official URL: http://dx.doi.org/10.1039/C2FD20140B
Abstract
The heteroaromatic ultraviolet chromophore pyrrole is found as a subunit in a number of important biomolecules: it is present in heme, the non-protein component of hemoglobin, and in the amino acid tryptophan. To date there have been several experimental studies, in both the time- and frequency-domains, which have interrogated the excited state dynamics of pyrrole. In this work, we specifically aim to unravel any differences in the H-atom elimination dynamics from pyrrole across an excitation wavelength range of 250–200 nm, which encompasses: (i) direct excitation to the (formally electric dipole forbidden) 11πσ* (1A2) state; and (ii) initial photoexcitation to the higher energy 1ππ* (1B2) state. This is achieved by using a combination of ultrafast time-resolved ion yield and time-resolved velocity map ion imaging techniques in the gas phase. Following direct excitation to 11πσ* (1A2) at 250 nm, we observe a single time-constant of 126 ± 28 fs for N–H bond fission. We assign this to tunnelling out of the quasi-bound 3s Rydberg component of the 11πσ* (1A2) surface in the vertical Franck–Condon region, followed by non-adiabatic coupling through a 11πσ*/S0 conical intersection to yield pyrrolyl radicals in their electronic ground state (C4H4N([X with combining tilde])) together with H-atoms. At 238 nm, direct excitation to, and N–H dissociation along, the 11πσ* (1A2) surface is observed to occur with a time-constant of 46 ± 22 fs. Upon initial population of the 1ππ* (1B2) state at 200 nm, a rapid 1ππ* (1B2) → 11πσ* (1A2) → N–H fission process takes place within 52 ± 12 fs. In addition to ultrafast N–H bond cleavage at 200 nm, we also observe the onset of statistical unimolecular H-atom elimination from vibrationally hot S0 ground state species, formed after the relaxation of excited electronic states, with a time-constant of 1.0 ± 0.4 ns. Analogous measurements on pyrrole-d1 reveal that these statistical H-atoms are released only through C–H bond cleavage.
Item Type: | Journal Article | ||||
---|---|---|---|---|---|
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||
Journal or Publication Title: | Faraday Discussions | ||||
Publisher: | Royal Society of Chemistry | ||||
ISSN: | 0301-7249 | ||||
Official Date: | 11 January 2013 | ||||
Dates: |
|
||||
Volume: | Volume 163 | ||||
Page Range: | pp. 95-116 | ||||
DOI: | 10.1039/c2fd20140b | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published | ||||
Access rights to Published version: | Restricted or Subscription Access |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |