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Fabrizia Negri - One of the best experts on this subject based on the ideXlab platform.
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evidence of dynamical jahn teller effect on triphenylene radical cation Resonance Raman Spectrum and ab initio quantum chemical calculations
Journal of Physical Chemistry A, 2000Co-Authors: Tamas Keszthelyi, Robert Wilbrandt, Gurusamy Balakrishnan, Atom W Yee, Fabrizia NegriAbstract:We report Resonance Raman Spectrum of the triphenylene radical cation generated by γ-irradiation in a Freon glass at 77 K. Raman spectra were obtained using excitation in Resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree−Fock, B-LYP, and B3-LYP, all with 6-31G basis set) were performed to obtain the equilibrium structures and vibrational force fields of triphenylene neutral and radical cation species. In addition, semiempirical calculations were carried out to identify the state in Resonance with the excitation light and to simulate the vibronic structure of the Resonance Raman Spectrum. From these experimental and theoretical results, it is concluded that the bands observed in the Resonance Raman Spectrum of the radical cation contain the signatures of the Jahn−Teller effect on the cation which, similarly to benzene cation, is dynamical in nature.
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Evidence of Dynamical Jahn−Teller Effect on Triphenylene Radical Cation: Resonance Raman Spectrum and ab Initio Quantum-Chemical Calculations
The Journal of Physical Chemistry A, 2000Co-Authors: Tamas Keszthelyi, Robert Wilbrandt, And Gurusamy Balakrishnan, W. Atom Yee, Fabrizia NegriAbstract:We report Resonance Raman Spectrum of the triphenylene radical cation generated by γ-irradiation in a Freon glass at 77 K. Raman spectra were obtained using excitation in Resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree−Fock, B-LYP, and B3-LYP, all with 6-31G basis set) were performed to obtain the equilibrium structures and vibrational force fields of triphenylene neutral and radical cation species. In addition, semiempirical calculations were carried out to identify the state in Resonance with the excitation light and to simulate the vibronic structure of the Resonance Raman Spectrum. From these experimental and theoretical results, it is concluded that the bands observed in the Resonance Raman Spectrum of the radical cation contain the signatures of the Jahn−Teller effect on the cation which, similarly to benzene cation, is dynamical in nature.
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The Resonance Raman Spectrum of cyclobutene
The Journal of Chemical Physics, 1995Co-Authors: Fabrizia Negri, Giorgio Orlandi, Francesco Zerbetto, Marek Z. ZgierskiAbstract:The vibronic pattern of the Resonance Raman Spectrum of cyclobutene is simulated by ab initio molecular orbital and by density functional theory calculations. Both Franck–Condon and Herzberg–Teller contributions are included in the analysis of the Spectrum. The results suggest an initial dynamics of cyclobutene in the S1 excited state in which the molecule attempts a cis–trans isomerization of the ethylene moiety.
John N. Moore - One of the best experts on this subject based on the ideXlab platform.
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The anti-Stokes Resonance Raman Spectrum of photoexcited S1 trans-stilbene
Chemical Physics Letters, 1995Co-Authors: Pavel Matousek, Ronald E. Hester, W. T. Toner, Michael Towrie, Anthony W. Parker, D.l.a. De Faria, John N. MooreAbstract:Abstract Anti-Stokes Resonance Raman spectra of S1 trans-stilbene have been measured for vibrational wavenumbers up to 1570 cm−1. Trans-stilbene in n-hexane was excited at 290–310 nm and probed at 580–620 nm, respectively, with 8 ps resolution. All the dominant bands seen in the Stokes Spectrum of the S1 state are also seen in the anti-Stokes Spectrum. Some anti-Stokes bands, notably those at 1570, 1240, 1180, 980, 720 and 285 cm−1, decrease markedly in relative intensity on a 2~ 10 ps timescale, displaying dynamics similar to those observed for the changes in the band position and bandwidth of several features in the Stokes Spectrum.
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Mode-Specific Temperature Dependence of the Resonance-Raman Spectrum of Trans-Stilbene in the Ground State
Springer Proceedings in Physics, 1994Co-Authors: W. T. Toner, Ronald E. Hester, Pavel Matousek, John N. Moore, A. W. Parker, Michael TowrieAbstract:New data on the steady state (cw) Resonance Raman Spectrum of So transstilbene are presented which show temperature dependent shifts of lines whose analogues in S1 trans-stilbene show similar but larger effects and also exhibit transient shifts and width changes [1,2].
David Lee Phillips - One of the best experts on this subject based on the ideXlab platform.
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Time-Resolved Resonance Raman and Density Functional Study of the Radical Cation of Chlorpromazine
The Journal of Physical Chemistry A, 2000Co-Authors: Duohai Pan, Lian C. T. Shoute, David Lee PhillipsAbstract:We have obtained a Resonance Raman Spectrum of the radical cation of promazine. We have also carried out density functional theory calculations to find the structures, hyperfme coupling constants (hfcc's), spin densities, and vibrational frequencies for the ground electronic states of the neutral chlorpromazine molecule and its radical cation. Preliminary vibrational assignments were made for all of the observed bands in the Resonance Raman Spectrum of the radical cation of chlorpromazine and in the FT-Raman Spectrum of the neutral chlorpromazine molecule. Our results indicate that the radical cation of chlorpromazine has a nonplanar structure similar to that of the radical cation of promazine. However, the chlorine atom at the 2 position in chlorpromazine appears to noticeably change the hfcc's and spin densities of the radical cation compared to the radical cation of promazine. This is possibly due to conjugation and/or through-bond interactions of the chlorine atom with the central-ring heterocycle.link_to_subscribed_fulltex
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time resolved Resonance Raman and density functional study of the radical cation of promazine
Journal of Physical Chemistry A, 1999Co-Authors: Lian C. T. Shoute, David Lee PhillipsAbstract:We have obtained a Resonance Raman Spectrum of the radical cation of promazine. We have also carried out density functional theory calculations to find the structures, hyperfine coupling constants (hfcc's), spin densities, and vibrational frequencies for the ground electronic states of the neutral chlorpromazine molecule and its radical cation. Preliminary vibrational assignments were made for all of the observed bands in the Resonance Raman Spectrum of the radical cation of chlorpromazine and in the FT-Raman Spectrum of the neutral chlorpromazine molecule. Our results indicate that the radical cation of chlorpromazine has a nonplanar structure similar to that of the radical cation of promazine. However, the chlorine atom at the 2 position in chlorpromazine appears to noticeably change the hfcc's and spin densities of the radical cation compared to the radical cation of promazine. This is possibly due to conjugation and/or through-bond interactions of the chlorine atom with the central-ring heterocycle.
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Time-Resolved Resonance Raman and Density Functional Study of the Radical Cation of Chlorpromazine
Journal of Physical Chemistry A, 1999Co-Authors: Duohai Pan, Lian C. T. Shoute, David Lee PhillipsAbstract:We have obtained a Resonance Raman Spectrum of the radical cation of promazine. We have also carried out density functional theory calculations to find the structures, hyperfine coupling constants (hfcc's), spin densities, and vibrational frequencies for the ground electronic states of the neutral chlorpromazine molecule and its radical cation. Preliminary vibrational assignments were made for all of the observed bands in the Resonance Raman Spectrum of the radical cation of chlorpromazine and in the FT-Raman Spectrum of the neutral chlorpromazine molecule. Our results indicate that the radical cation of chlorpromazine has a nonplanar structure similar to that of the radical cation of promazine. However, the chlorine atom at the 2 position in chlorpromazine appears to noticeably change the hfcc's and spin densities of the radical cation compared to the radical cation of promazine. This is possibly due to conjugation and/or through-bond interactions of the chlorine atom with the central-ring heterocycle.
Anthony W. Parker - One of the best experts on this subject based on the ideXlab platform.
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Radicals from One-Electron Oxidation of 4-Aminoresorcinol: Models for the Active Site Radical Intermediate in Copper Amine Oxidases
The Journal of Physical Chemistry B, 2000Co-Authors: Roger H. Bisby And, Steven A. Johnson, Anthony W. ParkerAbstract:Pulse radiolysis, laser flash photolysis, and time-resolved Resonance Raman spectroscopy have been used to study radicals derived by one-electron oxidation of 4-aminoresorcinol as models for the active site free-radical intermediate in the catalytic cycle of copper amine oxidases containing the trihydroxyphenylalanine (TOPA) quinone cofactor. The 4-aminoresorcinol radical at neutral pH has an absorption maximum at 450 nm, which is similar to that of the enzyme radical. At pH 5 the Resonance Raman Spectrum of the radical from one-electron oxidation of 4-aminoresorcinol resembles that in the enzyme. The radical protonates at lower pH values with a pKa of 3.4 to give a species with a blue shifted absorption and different Resonance Raman Spectrum. Time-resolved Resonance Raman spectroscopy shows that above pH 6.4 the radical from 4-aminoresorcinol deprotonates again to give a species that has a Resonance Raman Spectrum quite different from that of the enzyme radical. This second deprotonation is not immediate...
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Time-resolved Resonance Raman spectroscopy of the carbonate radical
Journal of the Chemical Society Faraday Transactions, 1998Co-Authors: Roger H. Bisby, Steven A. Johnson, Anthony W. Parker, Susan M. TavenderAbstract:The literature contains conflicting evidence regarding the protonation state of the carbonate radical, a species which now appears to be of biological significance. The time-resolved Resonance Raman Spectrum of CO3- has been observed. The radical was produced by oxidation of bicarbonate and carbonate using sulfate radicals at pH values from 7.5 to 12.3. The Resonance Raman Spectrum was found to be invariant with pH and contains a strongly polarised and intense band at 1062 cm-1. The Spectrum is consistent with the radical having C2v symmetry, indicating some distortion from the predicted D3h structure. The data suggest that the carbonate radical (CO3-) formed by one-electron oxidation of bicarbonate and carbonate does not undergo protonation to the conjugate acid, HCO3, as previously suggested with a pKa of 9.6. Some biochemical consequences of this are discussed.
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The anti-Stokes Resonance Raman Spectrum of photoexcited S1 trans-stilbene
Chemical Physics Letters, 1995Co-Authors: Pavel Matousek, Ronald E. Hester, W. T. Toner, Michael Towrie, Anthony W. Parker, D.l.a. De Faria, John N. MooreAbstract:Abstract Anti-Stokes Resonance Raman spectra of S1 trans-stilbene have been measured for vibrational wavenumbers up to 1570 cm−1. Trans-stilbene in n-hexane was excited at 290–310 nm and probed at 580–620 nm, respectively, with 8 ps resolution. All the dominant bands seen in the Stokes Spectrum of the S1 state are also seen in the anti-Stokes Spectrum. Some anti-Stokes bands, notably those at 1570, 1240, 1180, 980, 720 and 285 cm−1, decrease markedly in relative intensity on a 2~ 10 ps timescale, displaying dynamics similar to those observed for the changes in the band position and bandwidth of several features in the Stokes Spectrum.
Tamas Keszthelyi - One of the best experts on this subject based on the ideXlab platform.
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evidence of dynamical jahn teller effect on triphenylene radical cation Resonance Raman Spectrum and ab initio quantum chemical calculations
Journal of Physical Chemistry A, 2000Co-Authors: Tamas Keszthelyi, Robert Wilbrandt, Gurusamy Balakrishnan, Atom W Yee, Fabrizia NegriAbstract:We report Resonance Raman Spectrum of the triphenylene radical cation generated by γ-irradiation in a Freon glass at 77 K. Raman spectra were obtained using excitation in Resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree−Fock, B-LYP, and B3-LYP, all with 6-31G basis set) were performed to obtain the equilibrium structures and vibrational force fields of triphenylene neutral and radical cation species. In addition, semiempirical calculations were carried out to identify the state in Resonance with the excitation light and to simulate the vibronic structure of the Resonance Raman Spectrum. From these experimental and theoretical results, it is concluded that the bands observed in the Resonance Raman Spectrum of the radical cation contain the signatures of the Jahn−Teller effect on the cation which, similarly to benzene cation, is dynamical in nature.
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Evidence of Dynamical Jahn−Teller Effect on Triphenylene Radical Cation: Resonance Raman Spectrum and ab Initio Quantum-Chemical Calculations
The Journal of Physical Chemistry A, 2000Co-Authors: Tamas Keszthelyi, Robert Wilbrandt, And Gurusamy Balakrishnan, W. Atom Yee, Fabrizia NegriAbstract:We report Resonance Raman Spectrum of the triphenylene radical cation generated by γ-irradiation in a Freon glass at 77 K. Raman spectra were obtained using excitation in Resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree−Fock, B-LYP, and B3-LYP, all with 6-31G basis set) were performed to obtain the equilibrium structures and vibrational force fields of triphenylene neutral and radical cation species. In addition, semiempirical calculations were carried out to identify the state in Resonance with the excitation light and to simulate the vibronic structure of the Resonance Raman Spectrum. From these experimental and theoretical results, it is concluded that the bands observed in the Resonance Raman Spectrum of the radical cation contain the signatures of the Jahn−Teller effect on the cation which, similarly to benzene cation, is dynamical in nature.
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The radical cation of trans-1,3-pentadiene: Resonance Raman Spectrum and ab initio calculations
Journal of Molecular Structure, 1996Co-Authors: Tamas Keszthelyi, Robert WilbrandtAbstract:Abstract The Resonance Raman Spectrum of the trans -1,3-pentadiene radical cation generated by γ-irradiation in a Freon glass is reported. The Spectrum is excited at 532 nm in Resonance with the first absorption band. The Spectrum, which is interpreted with the help of density functional theory calculations, indicates the presence of both the s-trans and the s-cis rotamers of the trans -1,3-pentadiene radical cation.
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Radical Cation of 1,3-Butadiene: Resonance Raman Spectrum of the h6 Isotopomer
The Journal of Physical Chemistry, 1996Co-Authors: Tamas Keszthelyi, R. Wilbrandt, Thomas BallyAbstract:We report the Resonance Raman Spectrum of the 1,3-butadiene radical cation generated by γ-irradiation in a Freon glass. The Spectrum is excited at 550 nm in Resonance with the first absorption band. The Spectrum, which is interpreted with the help of density functional theory calculations and a recently published scaled quantum mechanical force field, indicates the presence of both the s-trans and the s-cis rotamers of the butadiene radical cation.