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Ilana Bar - One of the best experts on this subject based on the ideXlab platform.
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Vibrational overtone spectroscopy and Intramolecular Dynamics of ethene.
The journal of physical chemistry. A, 2007Co-Authors: Alexander Portnov, Evgeny Bespechansky, Ilana BarAbstract:The first through fourth C-H stretching overtone regions of ethene were measured by photoacoustic spectroscopy of room-temperature molecules and action spectroscopy of jet-cooled molecules. The rotational cooling led to improved resolution in the action spectra, turning these spectra into key players in determining the multiple band appearance in each region, their types, and origins. These manifolds arise from strong couplings of the C-H stretches to doorway states and were analyzed in terms of a simplified joint local-mode/normal-mode (LM)/(NM) model and an equivalent NM model, accounting for principal resonances. The diagonalization of the LM/NM and NM vibrational Hamiltonians and the least-square fittings revealed model parameters, enabling assignment of A- and B-type bands. These bands behave differently through the V = 2-4 manifolds, showing coupling to doorway states for the former but not for the latter. The energy flow out of the fourth C-H overtone is governed by the interaction with bath states due to the increase in the density of states.
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Intramolecular Dynamics from frequency domain spectroscopy
Vibrational Spectroscopy, 2006Co-Authors: Alexander Portnov, Yuval Ganot, Evgeny Bespachiansky, Salman Rosenwaks, Ilana BarAbstract:Abstract Vibrationally mediated photodissociation is emerging as a useful tool for studies of Intramolecular Dynamics in polyatomic molecules since it is a sensitive indicator of both the vibrational and electronic Dynamics. The method involves energy deposition in skeletal motions of molecules, their subsequent promotion to excited electronic states and dissociation. Jet-cooled action spectra, reflecting the yield of the ensuing atomic fragments as a function of vibrational excitation, are compared to simultaneously measured room temperature photoacoustic spectra and simulated spectra. The narrowed action spectra expose resonance splitting and enable estimating the homogeneous broadening and thus time scales for Intramolecular vibrational energy redistribution to close resonating states and to bath states. Overtone spectra of the acetylenic and alkyl C H stretches of the acetylene homologues, propyne and 1-butyne, demonstrate how the nature of rovibrationally excited states is highlighted by photolysis of pre-excited molecules.
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Vibrational spectroscopy and Intramolecular Dynamics of 1-butyne.
The Journal of chemical physics, 2004Co-Authors: Alexander Portnov, Salman Rosenwaks, Ilana BarAbstract:Photodissociation of jet-cooled vibrationally excited 1-butyne, C2H5C≡C–H, coupled with mass spectrometric detection of H photofragments, facilitated measurements of action spectra and Doppler profiles, expressing the yield of the ensuing fragments versus the vibrational excitation and UV probe lasers, respectively. Both the action spectra and the simultaneously measured room temperature photoacoustic spectra in the 2ν1, 3ν1, and 4ν1 C–H acetylenic stretch regions exhibit unresolved rotational envelopes with significant narrowing of the former due to temperature-related change in the rotational structure. The narrowing of the action spectrum in the 3ν1 region exposed a resonance splitting, implying Intramolecular vibrational energy redistribution (IVR) time of ≈1 ps. Asymmetric rotor simulation of the band contours provided the rotational constants and estimates for the homogeneous broadening arising from IVR to the bath vibrational states. The homogenous linewidth of 4ν1 is anomalously narrower than that...
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Intramolecular Dynamics in the photofragmentation of initially vibrationally excited CH2Cl2
The Journal of Physical Chemistry A, 2004Co-Authors: Ran Marom, Salman Rosenwaks, Amir Golan, Ilana BarAbstract:The Intramolecular Dynamics of dichloromethane was studied by applying vibrationally mediated photodissociation and photoacoustic spectroscopy. The parent species were initially excited to the second, third, and fourth C-H stretch overtone regions and subsequently photodissociated by ∼235 nm photons that also tagged the ground, Cl( 2 P 3 / 2 ) [Cl], and spin-orbit-excited, Cl( 2 P 1 / 2 ) [Cl*], state photofragments via resonantly enhanced multiphoton ionization. The Cl and Cl* action spectra revealed enhancement of their yield as a result of rovibrational excitation with a Cl*/Cl ratio of about ½. The action and photoacoustic spectra manifested a multiple-peak structure, which in terms of normal- and local-mode models is shown to be related to overtones of C-H stretches or combination bands of C-H stretches and bends. The measured time-of-flight profiles together with the determined Cl*/Cl branching ratios suggest fast dissociation and involvement of upper states of A' and A" symmetry, mixing via curve crossing and releasing both Cl and Cl*. The determined Cl*/Cl ratios in photodissociation of vibrationally excited CH 2 Cl 2 are higher than those obtained previously in 193 nm photodissociation of the vibrationless ground state, implying higher nonadiabaticity for the former.
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Photodissociation and Intramolecular Dynamics of vibrationally excited CHF2Cl
The Journal of Chemical Physics, 2002Co-Authors: Gabriela Dorfman, Salman Rosenwaks, A. Melchior, Ilana BarAbstract:Photodissociation of jet-cooled, vibrationally excited CHF2Cl molecules was studied in a time-of-flight mass spectrometer to elucidate bond rupture and Intramolecular Dynamics. The molecules were first excited with infrared photons to the N=3, N=7/2, and N=4 C–H stretch-bend polyad components, representing stretch-bend mixed states. They were then dissociated via promotion to excited electronic states by ∼235 or 243.135 nm photons, which also tagged 35Cl(2Pj) and 37Cl(2Pj) or H photofragments, respectively, by (2+1) resonantly enhanced multiphoton ionization. Comparison of the photofragment yield spectra to the simultaneously measured room-temperature infrared absorption spectra revealed significant narrowing of the former due to the reduction of rotational inhomogeneous structure. These spectra, and particularly the band contraction, afforded observation of resonance splitting in the vicinity of the 31, 34, 41, and 44 components, reflecting redistribution times in the range of 1–18 ps. These times manife...
Salman Rosenwaks - One of the best experts on this subject based on the ideXlab platform.
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Intramolecular Dynamics from frequency domain spectroscopy
Vibrational Spectroscopy, 2006Co-Authors: Alexander Portnov, Yuval Ganot, Evgeny Bespachiansky, Salman Rosenwaks, Ilana BarAbstract:Abstract Vibrationally mediated photodissociation is emerging as a useful tool for studies of Intramolecular Dynamics in polyatomic molecules since it is a sensitive indicator of both the vibrational and electronic Dynamics. The method involves energy deposition in skeletal motions of molecules, their subsequent promotion to excited electronic states and dissociation. Jet-cooled action spectra, reflecting the yield of the ensuing atomic fragments as a function of vibrational excitation, are compared to simultaneously measured room temperature photoacoustic spectra and simulated spectra. The narrowed action spectra expose resonance splitting and enable estimating the homogeneous broadening and thus time scales for Intramolecular vibrational energy redistribution to close resonating states and to bath states. Overtone spectra of the acetylenic and alkyl C H stretches of the acetylene homologues, propyne and 1-butyne, demonstrate how the nature of rovibrationally excited states is highlighted by photolysis of pre-excited molecules.
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Vibrational spectroscopy and Intramolecular Dynamics of 1-butyne.
The Journal of chemical physics, 2004Co-Authors: Alexander Portnov, Salman Rosenwaks, Ilana BarAbstract:Photodissociation of jet-cooled vibrationally excited 1-butyne, C2H5C≡C–H, coupled with mass spectrometric detection of H photofragments, facilitated measurements of action spectra and Doppler profiles, expressing the yield of the ensuing fragments versus the vibrational excitation and UV probe lasers, respectively. Both the action spectra and the simultaneously measured room temperature photoacoustic spectra in the 2ν1, 3ν1, and 4ν1 C–H acetylenic stretch regions exhibit unresolved rotational envelopes with significant narrowing of the former due to temperature-related change in the rotational structure. The narrowing of the action spectrum in the 3ν1 region exposed a resonance splitting, implying Intramolecular vibrational energy redistribution (IVR) time of ≈1 ps. Asymmetric rotor simulation of the band contours provided the rotational constants and estimates for the homogeneous broadening arising from IVR to the bath vibrational states. The homogenous linewidth of 4ν1 is anomalously narrower than that...
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Intramolecular Dynamics in the photofragmentation of initially vibrationally excited CH2Cl2
The Journal of Physical Chemistry A, 2004Co-Authors: Ran Marom, Salman Rosenwaks, Amir Golan, Ilana BarAbstract:The Intramolecular Dynamics of dichloromethane was studied by applying vibrationally mediated photodissociation and photoacoustic spectroscopy. The parent species were initially excited to the second, third, and fourth C-H stretch overtone regions and subsequently photodissociated by ∼235 nm photons that also tagged the ground, Cl( 2 P 3 / 2 ) [Cl], and spin-orbit-excited, Cl( 2 P 1 / 2 ) [Cl*], state photofragments via resonantly enhanced multiphoton ionization. The Cl and Cl* action spectra revealed enhancement of their yield as a result of rovibrational excitation with a Cl*/Cl ratio of about ½. The action and photoacoustic spectra manifested a multiple-peak structure, which in terms of normal- and local-mode models is shown to be related to overtones of C-H stretches or combination bands of C-H stretches and bends. The measured time-of-flight profiles together with the determined Cl*/Cl branching ratios suggest fast dissociation and involvement of upper states of A' and A" symmetry, mixing via curve crossing and releasing both Cl and Cl*. The determined Cl*/Cl ratios in photodissociation of vibrationally excited CH 2 Cl 2 are higher than those obtained previously in 193 nm photodissociation of the vibrationless ground state, implying higher nonadiabaticity for the former.
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Photodissociation and Intramolecular Dynamics of vibrationally excited CHF2Cl
The Journal of Chemical Physics, 2002Co-Authors: Gabriela Dorfman, Salman Rosenwaks, A. Melchior, Ilana BarAbstract:Photodissociation of jet-cooled, vibrationally excited CHF2Cl molecules was studied in a time-of-flight mass spectrometer to elucidate bond rupture and Intramolecular Dynamics. The molecules were first excited with infrared photons to the N=3, N=7/2, and N=4 C–H stretch-bend polyad components, representing stretch-bend mixed states. They were then dissociated via promotion to excited electronic states by ∼235 or 243.135 nm photons, which also tagged 35Cl(2Pj) and 37Cl(2Pj) or H photofragments, respectively, by (2+1) resonantly enhanced multiphoton ionization. Comparison of the photofragment yield spectra to the simultaneously measured room-temperature infrared absorption spectra revealed significant narrowing of the former due to the reduction of rotational inhomogeneous structure. These spectra, and particularly the band contraction, afforded observation of resonance splitting in the vicinity of the 31, 34, 41, and 44 components, reflecting redistribution times in the range of 1–18 ps. These times manife...
Donald L. Thompson - One of the best experts on this subject based on the ideXlab platform.
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Intramolecular Dynamics diffusion theory approach to complex unimolecular reactions
The Journal of Chemical Physics, 1999Co-Authors: Yin Guo, Dmitrii V. Shalashilin, Justin A. Krouse, Donald L. ThompsonAbstract:A further development of the Intramolecular Dynamics diffusion theory (IDDT) [J. Chem. Phys. 107, 6204 (1997)] for computing unimolecular reaction rate constants in the IVR-controlled regime is described. The approach is based on Kramers’ energy diffusion theory, with the reaction coordinate taken as the subsystem and the rest of the vibrational modes as the bath. The method provides a practical means of obtaining the rate constants in the IVR-controlled regime at considerable savings of computer time compared to the usual classical trajectory simulations. Its accuracy has been demonstrated in our earlier applications to some simple bond-fission reactions. In the study described here the idea of intrinsic reaction coordinate (IRC) is used to extend the IDDT approach to more complicated systems for which simple reaction coordinates are not easily identifiable. The basic idea is to take the IRC as the subsystem and the transverse vibrational modes as the bath. The method is applied to the unimolecular disso...
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CLASSICAL TRAJECTORY METHODS FOR POLYATOMIC MOLECULES
International Journal of Modern Physics B, 1997Co-Authors: Thomas D. Sewell, Donald L. ThompsonAbstract:Monte Carlo classical trajectory methods for simulating Intramolecular Dynamics, including chemical reactions, in large polyatomic molecules are described. Methods for performing calculations corresponding to various kinds of experiments are discussed. Some approaches for formulating potential-energy surfaces are described.
Alexander Portnov - One of the best experts on this subject based on the ideXlab platform.
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Vibrational overtone spectroscopy and Intramolecular Dynamics of ethene.
The journal of physical chemistry. A, 2007Co-Authors: Alexander Portnov, Evgeny Bespechansky, Ilana BarAbstract:The first through fourth C-H stretching overtone regions of ethene were measured by photoacoustic spectroscopy of room-temperature molecules and action spectroscopy of jet-cooled molecules. The rotational cooling led to improved resolution in the action spectra, turning these spectra into key players in determining the multiple band appearance in each region, their types, and origins. These manifolds arise from strong couplings of the C-H stretches to doorway states and were analyzed in terms of a simplified joint local-mode/normal-mode (LM)/(NM) model and an equivalent NM model, accounting for principal resonances. The diagonalization of the LM/NM and NM vibrational Hamiltonians and the least-square fittings revealed model parameters, enabling assignment of A- and B-type bands. These bands behave differently through the V = 2-4 manifolds, showing coupling to doorway states for the former but not for the latter. The energy flow out of the fourth C-H overtone is governed by the interaction with bath states due to the increase in the density of states.
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Intramolecular Dynamics from frequency domain spectroscopy
Vibrational Spectroscopy, 2006Co-Authors: Alexander Portnov, Yuval Ganot, Evgeny Bespachiansky, Salman Rosenwaks, Ilana BarAbstract:Abstract Vibrationally mediated photodissociation is emerging as a useful tool for studies of Intramolecular Dynamics in polyatomic molecules since it is a sensitive indicator of both the vibrational and electronic Dynamics. The method involves energy deposition in skeletal motions of molecules, their subsequent promotion to excited electronic states and dissociation. Jet-cooled action spectra, reflecting the yield of the ensuing atomic fragments as a function of vibrational excitation, are compared to simultaneously measured room temperature photoacoustic spectra and simulated spectra. The narrowed action spectra expose resonance splitting and enable estimating the homogeneous broadening and thus time scales for Intramolecular vibrational energy redistribution to close resonating states and to bath states. Overtone spectra of the acetylenic and alkyl C H stretches of the acetylene homologues, propyne and 1-butyne, demonstrate how the nature of rovibrationally excited states is highlighted by photolysis of pre-excited molecules.
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Vibrational spectroscopy and Intramolecular Dynamics of 1-butyne.
The Journal of chemical physics, 2004Co-Authors: Alexander Portnov, Salman Rosenwaks, Ilana BarAbstract:Photodissociation of jet-cooled vibrationally excited 1-butyne, C2H5C≡C–H, coupled with mass spectrometric detection of H photofragments, facilitated measurements of action spectra and Doppler profiles, expressing the yield of the ensuing fragments versus the vibrational excitation and UV probe lasers, respectively. Both the action spectra and the simultaneously measured room temperature photoacoustic spectra in the 2ν1, 3ν1, and 4ν1 C–H acetylenic stretch regions exhibit unresolved rotational envelopes with significant narrowing of the former due to temperature-related change in the rotational structure. The narrowing of the action spectrum in the 3ν1 region exposed a resonance splitting, implying Intramolecular vibrational energy redistribution (IVR) time of ≈1 ps. Asymmetric rotor simulation of the band contours provided the rotational constants and estimates for the homogeneous broadening arising from IVR to the bath vibrational states. The homogenous linewidth of 4ν1 is anomalously narrower than that...
Michał Kurzyński - One of the best experts on this subject based on the ideXlab platform.
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A synthetic picture of Intramolecular Dynamics of proteins. Towards a contemporary statistical theory of biochemical processes
Progress in biophysics and molecular biology, 1998Co-Authors: Michał KurzyńskiAbstract:Abstract An increasing body of experimental evidence indicates the slow character of internal Dynamics of native proteins. The important consequence of this is that theories of chemical reactions, used hitherto, appear inadequate for description of most biochemical reactions. Construction of a contemporary, truly advanced statistical theory of biochemical processes will need simple but realistic models of microscopic Dynamics of biomolecules. In this review, intended to be a contribution towards this direction, three topics are considered. First, an intentionally simplified picture of Dynamics of native proteins which emerges from recent investigations is presented. Fast vibrational modes of motion, of periods varying from 10 −14 to 10 −11 s, are contrasted with purely stochastic conformational transitions. Significant evidence is adduced that the relaxation time spectrum of the latter spreads in the whole range from 10 −11 to 10 5 s or longer, and up to 10 −7 s it is practically quasi-continuous. Next, the essential ideas of the theory of reaction rates based on stochastic models of Intramolecular Dynamics are outlined. Special attention is paid to reactions involving molecules in the initial conformational substrates confirmed to the transition state, which is realized in actual experimental situations. And finally, the two best experimentally justified classes of models of conformational transition Dynamics, symbolically referred to as “protein glass” and “protein machine”, are described and applied to the interpretation of a few simple biochemical processes. perhaps the most important result reported is the demonstration of the possibility of predominance of the short initial condition-dependent stage of protein involved reactions over the main stage described by the standard kinetics. This initial stage, and not the latter, is expected to be responsible for the coupling of component reactions in the complete enzymatic cycles as well as more complex processes of biological free energy transduction.