| 1. |
- Jenkins, Andrew J., et al.
(author)
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The Ehrenfest method with fully quantum nuclear motion (Qu-Eh) : Application to charge migration in radical cations
- 2018
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:9
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Journal article (peer-reviewed)abstract
- An algorithm is described for quantum dynamics where an Ehrenfest potential is combined with fully quantum nuclear motion (Quantum-Ehrenfest, Qu-Eh). The method is related to the single-set variational multi-configuration Gaussian approach (vMCG) but has the advantage that only a single quantum chemistry computation is required at each time step since there is only a single time-dependent potential surface. Also shown is the close relationship to the “exact factorization method.” The quantum Ehrenfest method is compared with vMCG for study of electron dynamics in a modified bismethylene-adamantane cation system. Illustrative examples of electron-nuclear dynamics are presented for a distorted allene system and for HCCI+ where one has a degenerate Π system.
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| 2. |
- Wu, Guorong, et al.
(author)
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Excited state non-adiabatic dynamics of N-methylpyrrole : A time-resolved photoelectron spectroscopy and quantum dynamics study
- 2016
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:1
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Journal article (peer-reviewed)abstract
- The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A(2)(pi sigma*) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B-1(pi 3p(y)) Rydberg state, followed by prompt internal conversion to the A(2)(pi sigma*) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A(2)(pi sigma*) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A(2)(pi sigma*) state, facilitating wavepacket motion around the potential barrier in the N-CH3 dissociation coordinate.
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| 3. |
- Wu, Guorong, et al.
(author)
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Excited state non-adiabatic dynamics of pyrrole : A time-resolved photoelectron spectroscopy and quantum dynamics study
- 2015
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 142:7
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Journal article (peer-reviewed)abstract
- The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole's electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A(2)(pi sigma*) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A(1)(pi pi*) and B-2(pi pi*) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole's electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B-1(pi sigma*) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B-1(pi sigma*) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A(2)(pi sigma*) state.
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