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Warren D. Lawrance - One of the best experts on this subject based on the ideXlab platform.
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Bound orbiting states of benzene–Ar and evidence for reversible intramolecular Vibrational Energy Redistribution within the complex
Chemical Physics Letters, 2005Co-Authors: Rebecca K Sampson, Warren D. LawranceAbstract:Abstract We have explored the proposition that emission from bound orbiting states of aromatic van der Waals complexes occurs where the free aromatic emits. Pumping 6 1 ¯ in benzene–Ar is predicted to lead, via intramolecular Vibrational Energy Redistribution (IVR), to excitation in van der Waals modes associated with 16 1 ¯ that are above the barrier to bound orbital motion. The 6 1 ¯ dispersed fluorescence spectrum shows a red-shaded, broad band with a maximum 21 cm −1 to the blue of the expected 6 1 0 16 1 1 ¯ transition, where the 6 1 0 16 1 1 band of free benzene occurs. The time dependence of the parent and growth bands in the 6 1 ¯ spectrum suggests that IVR from this level is reversible.
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The S1–S0(1B2–1A1) transition of jet‐cooled toluene: Excitation and dispersed fluorescence spectra, fluorescence lifetimes, and intramolecular Vibrational Energy Redistribution
Journal of Chemical Physics, 1996Co-Authors: Christopher G. Hickman, Jason R. Gascooke, Warren D. LawranceAbstract:The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet‐cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional Energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular Vibrational Energy Redistribution (IVR) at low S1 Vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 Vibrational Energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for ot...
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the s1 s0 1b2 1a1 transition of jet cooled toluene excitation and dispersed fluorescence spectra fluorescence lifetimes and intramolecular Vibrational Energy Redistribution
Journal of Chemical Physics, 1996Co-Authors: Christopher G. Hickman, Jason R. Gascooke, Warren D. LawranceAbstract:The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet‐cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional Energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular Vibrational Energy Redistribution (IVR) at low S1 Vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 Vibrational Energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for ot...
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Intramolecular Vibrational Energy Redistribution in S0 benzene at low Vibrational energies
Chemical Physics Letters, 1992Co-Authors: Narrelle T. Whetton, Warren D. LawranceAbstract:Abstract Rotationally resolved dispersed fluorescene spectra from the 6 1 level of benzene have been used to probe intramolecular Vibrational Energy Redistribution in the ground electronic state. The level 1 2 ( E vib =1986 cm −1 ) and 1 3 ( E vib =2979 cm −1 ) are observed to be each coupled to a single close-lying level. We propose that the pertubing levels are 5 2 in the case of 1 2 and 5 2 1 1 in the case of 1 3 . The coupling constant k 1155 has been determined to be 1.4 cm −1 .
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Calculations of Vibrational state mixing leading to intramolecular Vibrational Energy Redistribution in S1 anthracene: Comparison with quantum beat experiments
Journal of Chemical Physics, 1990Co-Authors: W. J. Bullock, D. K. Adams, Warren D. LawranceAbstract:A simple model for the anharmonic coupling constants has been used to calculate Vibrational state mixing in S1 anthracene. The aim of the calculations is to provide insight into the Vibrational state mixing responsible for intramolecular Vibrational Energy Redistribution (IVR). The calculations include all vibrations of the appropriate symmetry within a 100 cm−1 interval centered about the state of interest. The calculations are compared with experimental measurements of quantum beats in S1 anthracene [P. M. Felker and A. H. Zewail, J. Chem. Phys. 82, 2975 (1985)]. These experiments involved an investigation of rotational effects that established the coupling to be anharmonic in origin. We show that in order for the experimental data to be explained by anharmonic coupling alone, the high‐order anharmonic terms must be reasonably large. This implies that the anharmonic expansion converges quite slowly for EVIB≲2000 cm−1 in anthracene, in contrast with spectroscopic data for small molecules. Anthracene does...
Yanqiang Yang - One of the best experts on this subject based on the ideXlab platform.
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Elucidating the Coupling Mechanisms of Rapid Intramolecular Vibrational Energy Redistribution in Nitromethane: Ab Initio Molecular Dynamics Simulation.
Journal of Physical Chemistry A, 2020Co-Authors: Zhaoyang Zheng, Gangbei Zhu, Yuxiao Wang, Yanqiang YangAbstract:Ab initio molecular dynamics simulations are presented to investigate the intramolecular Vibrational Energy Redistribution (IVR) of an isolated nitromethane molecule. A number of IVR processes are ...
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ab initio molecular dynamics simulation of Vibrational Energy Redistribution of selective excitation of c h stretching vibrations for solid nitromethane
Physical Chemistry Chemical Physics, 2019Co-Authors: Zhaoyang Zheng, Gangbei Zhu, Yunfei Song, Yanqiang YangAbstract:Vibrational Energy Redistribution (VER) of energetic materials plays an important role in transferring the injected Energy to the hot spots, but it is extremely challenging to understand the mechanism of VER from experimental or theoretical studies. Here, we combined nonequilibrium molecular dynamics with density functional theory to study the processes of VER for solid nitromethane after the selective excitation of the C–H stretching vibration. The VER processes are traced by monitoring the normal-mode kinetic energies of both excited and unexcited vibrations. To explore the underlying VER mechanism, we also analyzed the spectral Energy density for the normal mode, obtained from the squared modulus of the short-time Fourier transition of their normal mode momentum. The results showed that the simulated VER progress was reproduced well compared with the previous 3D IR-Raman experiments of liquid nitromethane. Interestingly, the symmetric dependence of the coupling mechanism between the normal modes has been found.
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Ab initio molecular dynamics simulation of Vibrational Energy Redistribution of selective excitation of C–H stretching vibrations for solid nitromethane
Physical Chemistry Chemical Physics, 2019Co-Authors: Zhaoyang Zheng, Gangbei Zhu, Yunfei Song, Yanqiang YangAbstract:Vibrational Energy Redistribution (VER) of energetic materials plays an important role in transferring the injected Energy to the hot spots, but it is extremely challenging to understand the mechanism of VER from experimental or theoretical studies. Here, we combined nonequilibrium molecular dynamics with density functional theory to study the processes of VER for solid nitromethane after the selective excitation of the C–H stretching vibration. The VER processes are traced by monitoring the normal-mode kinetic energies of both excited and unexcited vibrations. To explore the underlying VER mechanism, we also analyzed the spectral Energy density for the normal mode, obtained from the squared modulus of the short-time Fourier transition of their normal mode momentum. The results showed that the simulated VER progress was reproduced well compared with the previous 3D IR-Raman experiments of liquid nitromethane. Interestingly, the symmetric dependence of the coupling mechanism between the normal modes has been found.
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Role of electron in intramolecular Vibrational Energy Redistribution: a simulation of time- and frequency-resolved CARS spectrum
RSC Advances, 2019Co-Authors: Zanhao Wang, Yunfei Song, Xiaosong Liu, Yanqiang YangAbstract:A coupled oscillator model with special attention to the electron is employed to simulate the time- and frequency-resolved coherent anti-Stokes Raman scattering (TFR-CARS) spectrum of benzene, where the electronic contribution is introduced as an oscillator as well as molecular vibration, and both the coupling between molecular vibrations and the coupling between electron and molecular vibration are involved. Through the simulation, the intramolecular Vibrational Energy Redistribution (IVR) process is confirmed to occur more readily between the molecular vibrations with the same Vibrational symmetry. Moreover, it is found that the electron plays a mediator role in the IVR process, and the coupling between electron and molecular vibration significantly increases the intramolecular Vibrational Energy transfer efficiency.
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Tracking intra-molecular electron and Vibrational Energy Redistribution by time and frequency resolved transient grating spectroscopy
Chemical Physics Letters, 2018Co-Authors: Wei Zhang, Xiaosong Liu, Yunfei Song, Lin Yan, Zanhao Wang, Yanqiang YangAbstract:Abstract Theoretical calculation results show that electron flow occurs from xanthene to phenyl ring within the Rh101 + after its electronic transition from ground state (S 0 ) to first excited state (S 1 ). Time and frequency resolved transient grating (TG) spectroscopy is then conducted to seek the experimental evidence. Through Fourier analysis at different wavelengths of TG signal and their specific value spectra, Vibrational enhancement corresponding to electron acceptor chromophore (phenyl ring) is observed. So the ultrafast Vibrational Energy Redistribution process is detected experimentally and the direction of electron flow is confirmed.
Christopher G. Hickman - One of the best experts on this subject based on the ideXlab platform.
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The S1–S0(1B2–1A1) transition of jet‐cooled toluene: Excitation and dispersed fluorescence spectra, fluorescence lifetimes, and intramolecular Vibrational Energy Redistribution
Journal of Chemical Physics, 1996Co-Authors: Christopher G. Hickman, Jason R. Gascooke, Warren D. LawranceAbstract:The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet‐cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional Energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular Vibrational Energy Redistribution (IVR) at low S1 Vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 Vibrational Energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for ot...
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the s1 s0 1b2 1a1 transition of jet cooled toluene excitation and dispersed fluorescence spectra fluorescence lifetimes and intramolecular Vibrational Energy Redistribution
Journal of Chemical Physics, 1996Co-Authors: Christopher G. Hickman, Jason R. Gascooke, Warren D. LawranceAbstract:The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet‐cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional Energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular Vibrational Energy Redistribution (IVR) at low S1 Vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 Vibrational Energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for ot...
John R. Barker - One of the best experts on this subject based on the ideXlab platform.
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On modeling the pressure-dependent photoisomerization of trans-stilbene by including slow intramolecular Vibrational Energy Redistribution.
Journal of Physical Chemistry A, 2006Co-Authors: Ralph E. Weston, John R. BarkerAbstract:Experimental data for the photoisomerization of trans-stilbene (S 1 ) in thermal bath gases at pressures up to 20 bar obtained previously by Meyer, Schroeder, and Troe (J. Phys. Chem. A 1999, 103, 10528-10539) are modeled by using a full collisional-reaction master equation that includes non-RRKM (Rice-Ramsperger-Kassel-Marcus) effects due to slow intramolecular Vibrational Energy Redistribution (IVR). The slow IVR effects are modeled by incorporating the theoretical results obtained recently by Leitner et al. (J. Phys. Chem. A 2003, 107, 10706-10716), who used the local random matrix theory. The present results show that the experimental rate constants of Meyer et al. are described to within about a factor of 2 over much of the experimental pressure range. However, a number of assumptions and areas of disagreement will require further investigation. These include a discrepancy between the calculated and experimental thermal rate constants near zero pressure, a leveling off of the experimental rate constants that is not predicted by theory and which depends on the identity of the collider gas, the need to use rate constants for collision-induced IVR that are larger than the estimated total collision rate constants, and the choice of barrier-crossing frequency. Despite these unsettled issues, the theory of Leitner et al. shows great promise for accounting for possible non-RRKM effects in an important class of reactions.
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Intramolecular Vibrational Energy Redistribution involving the torsion in CF3CH3: a molecular dynamics study.
Journal of Physical Chemistry A, 2006Co-Authors: Philip J. Stimac, John R. BarkerAbstract:Classical trajectory calculations on intramolecular Vibrational Energy Redistribution (IVR) involving the torsion in 1,1,1-trifluoroethane (TFE) are reported. Two potential Energy functions (PEFs) are used to describe the potential Energy surface. The “full” PEF gives excellent agreement with the experimental Vibrational frequencies. The “simple” PEF omits nondiagonal interaction terms, but still gives very good agreement with the experimental frequencies. The “simple” PEF is intended to minimize mode−mode coupling. Neither PEF includes the HF elimination reaction. Calculations are carried out both with nominal microcanonical selection of initial coordinates and momenta, and with a modified selection method that places controlled amounts of Energy in the torsion. Total (classical) Vibrational energies from 0.005 to 140 kcal mol-1 are investigated. The calculated time constants describing Energy flow out of the torsional mode are
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intramolecular Vibrational Energy Redistribution involving the torsion in cf3ch3 a molecular dynamics study
Journal of Physical Chemistry A, 2006Co-Authors: Philip J. Stimac, John R. BarkerAbstract:Classical trajectory calculations on intramolecular Vibrational Energy Redistribution (IVR) involving the torsion in 1,1,1-trifluoroethane (TFE) are reported. Two potential Energy functions (PEFs) are used to describe the potential Energy surface. The “full” PEF gives excellent agreement with the experimental Vibrational frequencies. The “simple” PEF omits nondiagonal interaction terms, but still gives very good agreement with the experimental frequencies. The “simple” PEF is intended to minimize mode−mode coupling. Neither PEF includes the HF elimination reaction. Calculations are carried out both with nominal microcanonical selection of initial coordinates and momenta, and with a modified selection method that places controlled amounts of Energy in the torsion. Total (classical) Vibrational energies from 0.005 to 140 kcal mol-1 are investigated. The calculated time constants describing Energy flow out of the torsional mode are <10 ps for classical Vibrational energies near the classical reaction thresho...
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Quasi-classical trajectory simulations of intramolecular Vibrational Energy Redistribution in HONO2 and DONO2.
Journal of Physical Chemistry B, 2005Co-Authors: Yong Liu, Lawrence L. Lohr, John R. BarkerAbstract:By use of an analytic potential Energy surface developed in this work for nitric acid, the quasi-classical trajectory method was used to simulate intramolecular Vibrational Energy Redistribution (IVR). A method was developed for monitoring the average Vibrational Energy in the OH (or OD) mode that uses the mean-square displacement of the bond length calculated during the trajectories. This method is effective for both rotating and nonrotating molecules. The calculated IVR time constant for HONO2 decreases exponentially with increasing excitation Energy, is almost independent of rotational temperature, and is in excellent agreement with the experimental determination (Bingemann, D.; Gorman, M. P.; King, A. M.; Crim, F. F. J. Chem. Phys. 1997, 107, 661). In DONO2, the IVR time constants show more complicated behavior with increasing excitation Energy, apparently due to 2:1 Fermi-resonance coupling with lower frequency modes. This effect should be measurable in experiments.
Hans-dieter Meyer - One of the best experts on this subject based on the ideXlab platform.
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Theoretical investigation of intramolecular Vibrational Energy Redistribution in HFCO and DFCO induced by an external field.
Journal of Chemical Physics, 2008Co-Authors: Gauthier Pasin, Christophe Iung, Fabien Gatti, Falk Richter, Céline Léonard, Hans-dieter MeyerAbstract:The present paper is devoted to a full quantum mechanical study of the intramolecular Vibrational Energy Redistribution in HFCO and DFCO. In contrast to our previous studies [Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007)], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state.
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Theoretical investigation of highly excited Vibrational states in DFCO: calculation of the out-of-plane bending states and simulation of the intramolecular Vibrational Energy Redistribution.
Journal of Chemical Physics, 2007Co-Authors: Gauthier Pasin, Christophe Iung, Fabien Gatti, Hans-dieter MeyerAbstract:A previously developed modified Davidson scheme [C. Iung and F. Ribeiro, J. Chem. Phys. 121, 174105 (2005)] is applied to compute and analyze highly excited (nu2,nu6) eigenstates in DFCO. The present paper is also devoted to the simulations of the intramolecular Vibrational Energy Redistribution (IVR) initiated by an excitation of the out-of-plane bending vibration (nnu6, n=2,4,6, . . . ,18, and 20). The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. A comprehensive comparison with experimental data as well as with previous simulations of IVR in HFCO [G. Pasin et al. J. Chem. Phys. 124, 194304 (2006)] is presented.
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Theoretical investigation of intramolecular Vibrational Energy Redistribution in highly excited HFCO.
Journal of Chemical Physics, 2006Co-Authors: Gauthier Pasin, Christophe Iung, Fabien Gatti, Hans-dieter MeyerAbstract:The present paper is devoted to the simulations of the intramolecular Vibrational Energy Redistribution (IVR) in HFCO initiated by an excitation of the out-of-plane bending vibration [nν6=2,4,6,…,18,20]. Using a full six-dimensional ab initio potential Energy, the multiconfiguration time-dependent Hartree (MCTDH) method was exploited to propagate the corresponding six-dimensional wave packets. This study emphasizes the stability of highly excited states of the out-of-plane bending mode which exist even above the dissociation threshold. More strikingly, the structure of the IVR during the first step of the dynamics is very stable for initial excitations ranging from 2ν6 to 20ν6. This latter result is consistent with the analysis of the eigenstates obtained, up to 10ν6, with the aid of the Davidson algorithm in a foregoing paper [Iung and Ribeiro, J. Chem. Phys. 121, 174105 (2005)]. The present study can be considered as complementary to this previous investigation. This paper also shows how MCTDH can be us...
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Theoretical investigation of intramolecular Vibrational Energy Redistribution in highly excited HFCO
Journal of Chemical Physics, 2006Co-Authors: Gauthier Pasin, Christophe Iung, Fabien Gatti, Hans-dieter MeyerAbstract:The present paper is devoted to the simulations of the intramolecular Vibrational Energy Redistribution IVR in HFCO initiated by an excitation of the out-of-plane bending vibration n 6=2,4,6, . . . ,18,20 . Using a full six-dimensional ab initio potential Energy, the multiconfiguration time-dependent Hartree MCTDH method was exploited to propagate the corresponding six-dimensional wave packets. This study emphasizes the stability of highly excited states of the out-of-plane bending mode which exist even above the dissociation threshold. More strikingly, the structure of the IVR during the first step of the dynamics is very stable for initial excitations ranging from 2 6 to 20 6. This latter result is consistent with the analysis of the eigenstates obtained, up to 10 6, with the aid of the Davidson algorithm in a foregoing paper Iung and Ribeiro, J. Chem. Phys. 121, 174105 2005 . The present study can be considered as complementary to this previous investigation. This paper also shows how MCTDH can be used to predict the dynamical behavior of a strongly excited system and to determine the energies of the corresponding highly excited states.
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Intramolecular Vibrational Energy Redistribution in toluene: a nine-dimensional quantum mechanical study using the MCTDH algorithm
Chemical Physics, 2004Co-Authors: Fabien Gatti, Hans-dieter MeyerAbstract:Abstract The intramolecular Vibrational Energy Redistribution within the methyl group of toluene is investigated. A nine-dimensional model potential Energy surface in curvilinear coordinates, derived by Cavagnat and Lespade, is adopted along with an exact nine-dimensional kinetic operator in polyspherical coordinates. The quantum calculations are performed with the multiconfiguration time-dependent Hartree (MCTDH) method. MCTDH and some recent extensions of the algorithm are briefly reviewed. We investigate the Vibrational Energy transfer which is initiated by a local CH-stretch excitation of 1–5 quanta. The Redistribution of Vibrational Energy strongly depends on the initial excitation, being most efficient for the v CH =3 excitation. Selected Energy levels are also computed, using a recently developed relaxation scheme as well as the filter-diagonalisation approach.
