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Article: Photodissociation of alkyl iodides in solution: Substituent effects on the early-time dynamics

TitlePhotodissociation of alkyl iodides in solution: Substituent effects on the early-time dynamics
Authors
Issue Date1991
PublisherAmerican Institute of Physics. The Journal's web site is located at http://jcp.aip.org/jcp/staff.jsp
Citation
The Journal Of Chemical Physics, 1991, v. 95 n. 1, p. 226-243 How to Cite?
AbstractResonance Raman spectra, including absolute scattering cross sections, have been measured for ethyl, isopropyl, and tert-butyl iodides in cyclohexane solution at seven to ten wavelengths between 303 and 200 nm. Spectra of fully deuterated ethyl iodide have also been obtained at five wavelengths. Spectra excited in the 300-250 nm region, on resonance with the directly dissociative A state, are dominated by long overtone progressions in the nominal C-I stretching mode near 500 cm-1. In all three molecules the fundamental of the C-I stretch is unexpectedly weak relative to the overtones when excited near the peak of the A band. This is shown to arise from interference between the A-state resonant part of the fundamental Raman amplitude and preresonant contributions from higher electronic states. In addition to the C-I stretching activity, A-state excitation generates significant intensity in fundamentals, overtones, and combination bands of modes nominally assigned as bending and CC stretching vibrations, suggesting a multidimensional character to the reaction coordinate. The absorption spectra and A-state resonant Raman intensities are modeled successfully through wave-packet propagation on a multidimensional locally harmonic potential with a preresonant contribution to the fundamental intensities included. The short-time photodissociation dynamics are then examined by using the normal-mode coefficients to convert the wave-packet motion from dimensionless normal coordinates into internal coordinates. It is found that while the dominant motion during the first 10 fs involves stretching of the C-I bond, other stretching and bending motions are also involved, although the precision of these conclusions for isopropyl and tert-butyl iodides is limited by the indeterminacy in the signs of the normal-mode displacements obtained from the intensity analysis. Comparison of the results for normal and perdeuterated ethyl iodide is used to resolve most of the sign indeterminacies for this molecule. The present results are compared and contrasted to conclusions of previous studies of energy partitioning in the vapor-phase photodissociation. © 1991 American Institute of Physics.
Persistent Identifierhttp://hdl.handle.net/10722/168153
ISSN
2015 Impact Factor: 2.894
2015 SCImago Journal Rankings: 0.959
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorPhillips, DLen_US
dc.contributor.authorMyers, ABen_US
dc.date.accessioned2012-10-08T03:15:43Z-
dc.date.available2012-10-08T03:15:43Z-
dc.date.issued1991en_US
dc.identifier.citationThe Journal Of Chemical Physics, 1991, v. 95 n. 1, p. 226-243en_US
dc.identifier.issn0021-9606en_US
dc.identifier.urihttp://hdl.handle.net/10722/168153-
dc.description.abstractResonance Raman spectra, including absolute scattering cross sections, have been measured for ethyl, isopropyl, and tert-butyl iodides in cyclohexane solution at seven to ten wavelengths between 303 and 200 nm. Spectra of fully deuterated ethyl iodide have also been obtained at five wavelengths. Spectra excited in the 300-250 nm region, on resonance with the directly dissociative A state, are dominated by long overtone progressions in the nominal C-I stretching mode near 500 cm-1. In all three molecules the fundamental of the C-I stretch is unexpectedly weak relative to the overtones when excited near the peak of the A band. This is shown to arise from interference between the A-state resonant part of the fundamental Raman amplitude and preresonant contributions from higher electronic states. In addition to the C-I stretching activity, A-state excitation generates significant intensity in fundamentals, overtones, and combination bands of modes nominally assigned as bending and CC stretching vibrations, suggesting a multidimensional character to the reaction coordinate. The absorption spectra and A-state resonant Raman intensities are modeled successfully through wave-packet propagation on a multidimensional locally harmonic potential with a preresonant contribution to the fundamental intensities included. The short-time photodissociation dynamics are then examined by using the normal-mode coefficients to convert the wave-packet motion from dimensionless normal coordinates into internal coordinates. It is found that while the dominant motion during the first 10 fs involves stretching of the C-I bond, other stretching and bending motions are also involved, although the precision of these conclusions for isopropyl and tert-butyl iodides is limited by the indeterminacy in the signs of the normal-mode displacements obtained from the intensity analysis. Comparison of the results for normal and perdeuterated ethyl iodide is used to resolve most of the sign indeterminacies for this molecule. The present results are compared and contrasted to conclusions of previous studies of energy partitioning in the vapor-phase photodissociation. © 1991 American Institute of Physics.en_US
dc.languageengen_US
dc.publisherAmerican Institute of Physics. The Journal's web site is located at http://jcp.aip.org/jcp/staff.jspen_US
dc.relation.ispartofThe Journal of Chemical Physicsen_US
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.rightsCopyright (1991) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (The Journal Of Chemical Physics, 1991, v. 95 n. 1, p. 226-243) and may be found at (http://jcp.aip.org.eproxy2.lib.hku.hk/resource/1/jcpsa6/v95/i1/p226_s1).-
dc.titlePhotodissociation of alkyl iodides in solution: Substituent effects on the early-time dynamicsen_US
dc.typeArticleen_US
dc.identifier.emailPhillips, DL:phillips@hku.hken_US
dc.identifier.authorityPhillips, DL=rp00770en_US
dc.description.naturepublished_or_final_versionen_US
dc.identifier.doi10.1063/1.461479-
dc.identifier.scopuseid_2-s2.0-36449006101en_US
dc.identifier.volume95en_US
dc.identifier.issue1en_US
dc.identifier.spage226en_US
dc.identifier.epage243en_US
dc.identifier.isiWOS:A1991FT84700024-
dc.publisher.placeUnited Statesen_US
dc.identifier.scopusauthoridPhillips, DL=7404519365en_US
dc.identifier.scopusauthoridMyers, AB=7202743342en_US

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