Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes via site-selective ionization

Weronika O Razmus, Felix Allum, James Harries, Yoshiaki Kumagai, Kiyonobu Nagaya, Surjendu Bhattacharyya, Mathew Britton, Mark Brouard, Philip H Bucksbaum, Kieran Cheung, Stuart W Crane, Mizuho Fushitani, Ian Gabalski, Tatsuo Gejo, Aaron Ghrist, David Heathcote, Yasumasa Hikosaka, Akiyoshi Hishikawa, Paul Hockett, Ellen JonesEdwin Kukk, Hiroshi Iwayama, Huynh V S Lam, Joseph W McManus, Dennis Milesevic, Jochen Mikosch, Shinichirou Minemoto, Akinobu Niozu, Andrew J Orr-Ewing, Shigeki Owada, Daniel Rolles, Artem Rudenko, Dave Townsend, Kiyoshi Ueda, James Unwin, Claire Vallance, Anbu Venkatachalam, Shin-ichi Wada, Tiffany Walmsley, Emily M Warne, Joanne L Woodhouse, Michael Burt, Michael N R Ashfold, Russell S Minns*, Ruaridh Forbes*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


C–I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy. At greater C-I separations, beyond the critical distance, CT is no longer possible and the measured kinetic energies of the charged iodine atoms report on the neutral dissociation process. The time and momentum resolved measurements allow determination of the timescales and the respective product momentum and kinetic energy distributions for both isomers, which are interpreted in terms of rival ‘direct’ and ‘indirect’ dissociation pathways. The measurements are compared with a classical over the barrier model, which reveals that the onset of the indirect dissociation process is delayed by ∼ 1 ps relative to the direct process. The kinetics of the two processes show no discernible difference between the two parent isomers, but the branching between the direct and indirect dissociation channels and the respective product momentum distributions show isomer dependencies. The greater relative yield of indirect dissociation products from 262 nm photolysis of 3-iodothiophene (cf. 2-iodothiophene) is attributed to the different partial cross-sections for (ring-centred) π∗ ← π and (C-I bond localized) σ∗ ← (n/π) excitation in the respective parent isomers.
Original languageEnglish
Pages (from-to)12725-12737
Number of pages13
JournalPhysical Chemistry Chemical Physics
Issue number16
Early online date5 Apr 2024
Publication statusE-pub ahead of print - 5 Apr 2024

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© 2024 The Royal Society of Chemistry.


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