nσ* and πσ* excited states in aryl halide photochemistry: a comprehensive study of the UV photodissociation dynamics ofiodobenzene
Identifieur interne : 006544 ( Main/Exploration ); précédent : 006543; suivant : 006545nσ* and πσ* excited states in aryl halide photochemistry: a comprehensive study of the UV photodissociation dynamics ofiodobenzene
Auteurs : Alan G. Sage [Royaume-Uni] ; Thomas A. A. Oliver [Royaume-Uni] ; Daniel Murdock [Royaume-Uni] ; Martin B. Crow ; Grant A. D. Ritchie ; Jeremy N. Harvey [Royaume-Uni] ; Michael N. R. Ashfold [Royaume-Uni]Source :
- PCCP. Physical chemistry chemical physics : (Print) [ 1463-9076 ] ; 2011.
Descripteurs français
- Pascal (Inist)
- Etat excité, Aryle, Halogénure, Photochimie, Photodissociation, Dynamique, Article synthèse, Dissociation moléculaire, Excitation impact électron, Orbitale, Hydrure, Vitesse déplacement, Ion, Formation image, Laser IR, Structure électronique, Calcul ab initio, Phase gazeuse, Distribution angulaire, Photolyse, Longueur onde, Fragment, pH, Etat vibrationnel, Spin, Rapport branchement, Iode, Surface énergie potentielle, Energie, Anisotropie, 3380G, 3115A.
- Wicri :
- topic : Photochimie, Iode.
English descriptors
- KwdEn :
- Ab initio calculations, Angular distribution, Anisotropy, Aryl, Branching ratio, Dynamics, Electron impact excitation, Electronic structure, Energy, Excited state, Fragment, Gas phase, Halides, Hydrides, Imaging, Infrared laser, Iodine, Ions, Molecular dissociation, Orbital, Photochemistry, Photodissociation, Photolysis, Potential energy surfaces, Review, Speed, Spin, Vibrational states, Wavelength, pH.
Abstract
A recent review (Ashfold et al., Phys. Chem. Chem. Phys., 2010, 12, 1218) highlighted the important role of dissociative excited states formed by electron promotion to σ* orbitals in establishing the photochemistry of many molecular hydrides. Here we extend such considerations to molecular halides, with a particular focus on iodobenzene. Two experimental techniques (velocity mapped ion imaging (VMI) and time resolved infrared (IR) diode laser absorption) and electronic structure calculations have been employed in a comprehensive study of the near ultraviolet (UV) photodissociation of gas phase iodobenzene molecules. The VMI studies yield the speeds and angular distributions of the I(2P3/2) and I*(2P1/2) photofragments formed by photolysis in the wavelength range 330 ≥ λ ≥ 206 nm. Four distinct dissociation channels are observed for the I(2P3/2) atom products, and a further three channels for the I*(2P1/2) fragments. The phenyl (Ph) radical partners formed via one particular I* product channel following excitation at wavelengths 305 ≥ λ ≥ 250 nm are distributed over a sufficiently select sub-set of vibrational (v) states that the images allow resolution of specific I* + Ph(v) channels, identification of the active product mode (v10, an in-plane ring breathing mode), and a refined determination of D0(Ph-I) = 23 390 ± 50 cm-1. The time-resolved IR absorption studies allow determination of the spin-orbit branching ratio in the iodine atom products formed at λ = 248 nm (φI* = [I*]/([I] + [I*]) = 0.28 ± 0.04) and at 266 nm (φI* = 0.32 ± 0.05). The complementary high-level, spin-orbit resolved ab initio calculations of sections (along the C-I bond coordinate) through the ground and first 19 excited state potential energy surfaces (PESs) reveal numerous excited states in the energy range of current interest. Except at the very shortest wavelength, however, all of the observed I and I* products display limiting or near limiting parallel recoil anisotropy. This encourages discussion of the fragmentation dynamics in terms of excitation to states of A1 total symmetry and dissociation on the 2A, and 4A, (σ* ← n/π) PESs to yield, respectively, I and I* products, or via non-adiabatic coupling to other σ* ← n/π PESs that correlate to these respective limits. Similarities (and differences) with the available UV photochemical data for the other aryl halides, and with the simpler (and more thoroughly studied) iodides HI and CH3I, are summarised.
Affiliations:
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Sage</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>School of Chemistry, University of Bristol</s1><s2>Bristol BS8 1TS</s2><s3>GBR</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ><sZ>6 aut.</sZ><sZ>7 aut.</sZ></inist:fA14><country>Royaume-Uni</country><wicri:noRegion>Bristol BS8 1TS</wicri:noRegion></affiliation></author><author><name sortKey="Oliver, Thomas A A" sort="Oliver, Thomas A A" uniqKey="Oliver T" first="Thomas A. A." last="Oliver">Thomas A. A. Oliver</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>School of Chemistry, University of Bristol</s1><s2>Bristol BS8 1TS</s2><s3>GBR</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ><sZ>6 aut.</sZ><sZ>7 aut.</sZ></inist:fA14><country>Royaume-Uni</country><wicri:noRegion>Bristol BS8 1TS</wicri:noRegion></affiliation></author><author><name sortKey="Murdock, Daniel" sort="Murdock, Daniel" uniqKey="Murdock D" first="Daniel" last="Murdock">Daniel Murdock</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>School of Chemistry, University of Bristol</s1><s2>Bristol BS8 1TS</s2><s3>GBR</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ><sZ>6 aut.</sZ><sZ>7 aut.</sZ></inist:fA14><country>Royaume-Uni</country><wicri:noRegion>Bristol BS8 1TS</wicri:noRegion></affiliation></author><author><name sortKey="Crow, Martin B" sort="Crow, Martin B" uniqKey="Crow M" first="Martin B." last="Crow">Martin B. Crow</name></author><author><name sortKey="Ritchie, Grant A D" sort="Ritchie, Grant A D" uniqKey="Ritchie G" first="Grant A. D." last="Ritchie">Grant A. D. Ritchie</name></author><author><name sortKey="Harvey, Jeremy N" sort="Harvey, Jeremy N" uniqKey="Harvey J" first="Jeremy N." last="Harvey">Jeremy N. Harvey</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>School of Chemistry, University of Bristol</s1><s2>Bristol BS8 1TS</s2><s3>GBR</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ><sZ>6 aut.</sZ><sZ>7 aut.</sZ></inist:fA14><country>Royaume-Uni</country><wicri:noRegion>Bristol BS8 1TS</wicri:noRegion></affiliation></author><author><name sortKey="Ashfold, Michael N R" sort="Ashfold, Michael N R" uniqKey="Ashfold M" first="Michael N. R." last="Ashfold">Michael N. R. Ashfold</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>School of Chemistry, University of Bristol</s1><s2>Bristol BS8 1TS</s2><s3>GBR</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ><sZ>6 aut.</sZ><sZ>7 aut.</sZ></inist:fA14><country>Royaume-Uni</country><wicri:noRegion>Bristol BS8 1TS</wicri:noRegion></affiliation></author></analytic><series><title level="j" type="main">PCCP. Physical chemistry chemical physics : (Print)</title><title level="j" type="abbreviated">PCCP, Phys. chem. chem. phys. : (Print)</title><idno type="ISSN">1463-9076</idno><imprint><date when="2011">2011</date></imprint></series></biblStruct></sourceDesc><seriesStmt><title level="j" type="main">PCCP. Physical chemistry chemical physics : (Print)</title><title level="j" type="abbreviated">PCCP, Phys. chem. chem. phys. : (Print)</title><idno type="ISSN">1463-9076</idno></seriesStmt></fileDesc><profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Ab initio calculations</term><term>Angular distribution</term><term>Anisotropy</term><term>Aryl</term><term>Branching ratio</term><term>Dynamics</term><term>Electron impact excitation</term><term>Electronic structure</term><term>Energy</term><term>Excited state</term><term>Fragment</term><term>Gas phase</term><term>Halides</term><term>Hydrides</term><term>Imaging</term><term>Infrared laser</term><term>Iodine</term><term>Ions</term><term>Molecular dissociation</term><term>Orbital</term><term>Photochemistry</term><term>Photodissociation</term><term>Photolysis</term><term>Potential energy surfaces</term><term>Review</term><term>Speed</term><term>Spin</term><term>Vibrational states</term><term>Wavelength</term><term>pH</term></keywords><keywords scheme="Pascal" xml:lang="fr"><term>Etat excité</term><term>Aryle</term><term>Halogénure</term><term>Photochimie</term><term>Photodissociation</term><term>Dynamique</term><term>Article synthèse</term><term>Dissociation moléculaire</term><term>Excitation impact électron</term><term>Orbitale</term><term>Hydrure</term><term>Vitesse déplacement</term><term>Ion</term><term>Formation image</term><term>Laser IR</term><term>Structure électronique</term><term>Calcul ab initio</term><term>Phase gazeuse</term><term>Distribution angulaire</term><term>Photolyse</term><term>Longueur onde</term><term>Fragment</term><term>pH</term><term>Etat vibrationnel</term><term>Spin</term><term>Rapport branchement</term><term>Iode</term><term>Surface énergie potentielle</term><term>Energie</term><term>Anisotropie</term><term>3380G</term><term>3115A</term></keywords><keywords scheme="Wicri" type="topic" xml:lang="fr"><term>Photochimie</term><term>Iode</term></keywords></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">A recent review (Ashfold et al., Phys. Chem. Chem. Phys., 2010, 12, 1218) highlighted the important role of dissociative excited states formed by electron promotion to σ<sup>*</sup> orbitals in establishing the photochemistry of many molecular hydrides. Here we extend such considerations to molecular halides, with a particular focus on iodobenzene. Two experimental techniques (velocity mapped ion imaging (VMI) and time resolved infrared (IR) diode laser absorption) and electronic structure calculations have been employed in a comprehensive study of the near ultraviolet (UV) photodissociation of gas phase iodobenzene molecules. The VMI studies yield the speeds and angular distributions of the I(<sup>2</sup>P<sub>3/2</sub>) and I<sup>*</sup>(<sup>2</sup>P<sub>1/2</sub>) photofragments formed by photolysis in the wavelength range 330 ≥ λ ≥ 206 nm. Four distinct dissociation channels are observed for the I(<sup>2</sup>P<sub>3/2</sub>) atom products, and a further three channels for the I<sup>*</sup>(<sup>2</sup>P<sub>1/2</sub>) fragments. The phenyl (Ph) radical partners formed via one particular I<sup>*</sup> product channel following excitation at wavelengths 305 ≥ λ ≥ 250 nm are distributed over a sufficiently select sub-set of vibrational (v) states that the images allow resolution of specific I<sup>*</sup> + Ph(v) channels, identification of the active product mode (v<sub>10</sub>, an in-plane ring breathing mode), and a refined determination of D<sub>0</sub>(Ph-I) = 23 390 ± 50 cm<sup>-1</sup>. The time-resolved IR absorption studies allow determination of the spin-orbit branching ratio in the iodine atom products formed at λ = 248 nm (φ<sub>I* </sub>= [I<sup>*</sup>]/([I] + [I<sup>*</sup>]) = 0.28 ± 0.04) and at 266 nm (φ<sub>I*</sub> = 0.32 ± 0.05). The complementary high-level, spin-orbit resolved ab initio calculations of sections (along the C-I bond coordinate) through the ground and first 19 excited state potential energy surfaces (PESs) reveal numerous excited states in the energy range of current interest. Except at the very shortest wavelength, however, all of the observed I and I<sup>*</sup> products display limiting or near limiting parallel recoil anisotropy. This encourages discussion of the fragmentation dynamics in terms of excitation to states of A<sub>1</sub> total symmetry and dissociation on the 2A, and 4A, (σ<sup>*</sup> ← n/π) PESs to yield, respectively, I and I<sup>*</sup> products, or via non-adiabatic coupling to other σ<sup>*</sup> ← n/π PESs that correlate to these respective limits. Similarities (and differences) with the available UV photochemical data for the other aryl halides, and with the simpler (and more thoroughly studied) iodides HI and CH<sub>3</sub>I, are summarised.</div></front></TEI><affiliations><list><country><li>Royaume-Uni</li></country></list><tree><noCountry><name sortKey="Crow, Martin B" sort="Crow, Martin B" uniqKey="Crow M" first="Martin B." last="Crow">Martin B. Crow</name><name sortKey="Ritchie, Grant A D" sort="Ritchie, Grant A D" uniqKey="Ritchie G" first="Grant A. D." last="Ritchie">Grant A. D. Ritchie</name></noCountry><country name="Royaume-Uni"><noRegion><name sortKey="Sage, Alan G" sort="Sage, Alan G" uniqKey="Sage A" first="Alan G." last="Sage">Alan G. Sage</name></noRegion><name sortKey="Ashfold, Michael N R" sort="Ashfold, Michael N R" uniqKey="Ashfold M" first="Michael N. R." last="Ashfold">Michael N. R. Ashfold</name><name sortKey="Harvey, Jeremy N" sort="Harvey, Jeremy N" uniqKey="Harvey J" first="Jeremy N." last="Harvey">Jeremy N. Harvey</name><name sortKey="Murdock, Daniel" sort="Murdock, Daniel" uniqKey="Murdock D" first="Daniel" last="Murdock">Daniel Murdock</name><name sortKey="Oliver, Thomas A A" sort="Oliver, Thomas A A" uniqKey="Oliver T" first="Thomas A. A." last="Oliver">Thomas A. A. Oliver</name></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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