skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

Abstract

Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region of the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known frommore » the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for theoretical calculations on the nature of core-excited states in halogenated hydrocarbons, especially in the transition state region along the C—I reaction coordinate.« less

Authors:
;  [1];  [2];  [1];  [2];  [2]
  1. Department of Chemistry, University of California, Berkeley, California 94720 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22657861
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 144; Journal Issue: 12; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; ALLYL RADICALS; BRANCHING RATIO; COMPUTER CALCULATIONS; DISSOCIATION; ELECTRONIC STRUCTURE; EXCITATION; EXCITED STATES; EXTREME ULTRAVIOLET RADIATION; IODIDES; IODINE; METHYL IODIDE; PHOTOLYSIS; TRANSIENTS

Citation Formats

Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Leone, Stephen R., E-mail: srl@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Department of Physics, University of California, Berkeley, California 94720. Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study. United States: N. p., 2016. Web. doi:10.1063/1.4944930.
Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Leone, Stephen R., E-mail: srl@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, & Department of Physics, University of California, Berkeley, California 94720. Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study. United States. doi:10.1063/1.4944930.
Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Leone, Stephen R., E-mail: srl@berkeley.edu, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Department of Physics, University of California, Berkeley, California 94720. Mon . "Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study". United States. doi:10.1063/1.4944930.
@article{osti_22657861,
title = {Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study},
author = {Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu and Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 and Leone, Stephen R., E-mail: srl@berkeley.edu and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 and Department of Physics, University of California, Berkeley, California 94720},
abstractNote = {Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region of the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for theoretical calculations on the nature of core-excited states in halogenated hydrocarbons, especially in the transition state region along the C—I reaction coordinate.},
doi = {10.1063/1.4944930},
journal = {Journal of Chemical Physics},
number = 12,
volume = 144,
place = {United States},
year = {Mon Mar 28 00:00:00 EDT 2016},
month = {Mon Mar 28 00:00:00 EDT 2016}
}