Excited state dynamics of CH2I2 and CH2BrI studied with UV pump VUV probe photoelectron spectroscopy

Spencer L Horton; Yusong Liu; Ruaridh Forbes; Varun Makhija; Rune Lausten; Albert Stolow; Paul Hockett; Philipp Marquetand; Tamás Rozgonyi; Thomas Weinacht

doi:10.1063/1.5086665

Excited state dynamics of CH₂I₂ and CH₂BrI studied with UV pump VUV probe photoelectron spectroscopy

J Chem Phys. 2019 May 7;150(17):174201. doi: 10.1063/1.5086665.

Authors

Affiliations

¹ Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA.
² Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada.
³ National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
⁴ Faculty of Chemistry, Institute of Theoretical Chemistry, University of Vienna, Währinger Str. 17, 1090 Wien, Austria.
⁵ Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok Körútja 2, Budapest 1117, Hungary.

PMID: 31067867
DOI: 10.1063/1.5086665

Abstract

We compare the excited state dynamics of diiodomethane (CH₂I₂) and bromoiodomethane (CH₂BrI) using time resolved photoelectron spectroscopy. A 4.65 eV UV pump pulse launches a dissociative wave packet on excited states of both molecules and the ensuing dynamics are probed via photoionization using a 7.75 eV probe pulse. The resulting photoelectrons are measured with the velocity map imaging technique for each pump-probe delay. Our measurements highlight differences in the dynamics for the two molecules, which are interpreted with high-level ab initio molecular dynamics (trajectory surface hopping) calculations. Our analysis allows us to associate features in the photoelectron spectrum with different portions of the excited state wave packet represented by different trajectories. The excited state dynamics in bromoiodomethane are simple and can be described in terms of direct dissociation along the C-I coordinate, whereas the dynamics in diiodomethane involve internal conversion and motion along multiple dimensions.