UV Photodissociation of Pyrroles: Symmetry and Substituent Effects

Karsili, Tolga N. V.; Marchetti, Barbara; Moca, Roberta; Ashfold, Michael N. R.

doi:10.1021/jp404580v

Cited by 26 publications

(59 citation statements)

References 28 publications

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“…This is a direct result of DMP r being populated in only a limited set of vibrational states, predominately in v = 0. This result is in excellent agreement with the H Rydberg atom photofragment translational spectroscopy (HRA-PTS) studies of Karsili et al 14 Through consideration of the above energetics, we can determine the TKER for dissociation into DMP r and H atom photofragments according to the relationship…”

Section: Resultssupporting

confidence: 88%

Ultrafast Excited-State Dynamics of 2,4-Dimethylpyrrole

et al. 2014

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The dynamics of photoexcited 2,4-dimethylpyrrole (DMP) were studied using time-resolved velocity map imaging spectroscopy over a range of photoexcitation wavelengths (276-238 nm). Two dominant H atom elimination channels were inferred from the time-resolved total kinetic energy release spectra, one which occurs with a time constant of ∼120 fs producing H atoms with high kinetic energies centered around 5000-7000 cm(-1) and a second channel with a time constant of ∼3.5 ps producing H atoms with low kinetic energies centered around 2500-3000 cm(-1). The first of these channels is attributed to direct excitation from the ground electronic state (S0) to the dissociative 1(1)πσ* state (S1) and subsequent N-H bond fission, moderated by a reaction barrier in the N-H stretch coordinate. In contrast to analogous measurements in pyrrole (Roberts et al. Faraday Discuss. 2013, 163, 95-116), the N-H dissociation times are invariant with photoexcitation wavelength, implying a relatively flatter potential in the vertical Franck-Condon region of the 1(1)πσ* state of DMP. The origins of the second channel are less clear-cut, but given the picosecond time constant for this process, we posit that this channel is indirect and is likely a consequence of populating higher-lying electronic states [e.g., 2(1)πσ* (S2)] which, following vibronic coupling into lower-lying intermediary states (namely, S1 or S0), leads to prompt N-H bond fission.

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Section: Resultssupporting

confidence: 88%

Ultrafast Excited-State Dynamics of 2,4-Dimethylpyrrole

et al. 2014

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“…Since the ex-tremely low oscillator strength of the πσ * state seems to place the observation of its dynamics below the sensitivity of the applied experimental technique, the study of pyrrole methylated derivatives as 2-5dimethylpyrrole and N-methylpyrrole, which retaining the same relevant electronic structure, permits a more efficient photoexcitation 44,55,56 that could provide highly relevant dynamical data. Experiments on these species are being run in our lab at the present time.…”

Section: Discussionmentioning

confidence: 99%

Revisiting the relaxation dynamics of isolated pyrrole

Montero

Ovejas

Fernández-Fernández

et al. 2014

The Journal of Chemical Physics

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Herein, the interpretation of the femtosecond-scale temporal evolution of the pyrrole ion signal, after excitation in the 267-217 nm interval, recently published by our group [R. Montero, A. Peralta Conde, V. Ovejas, M. Fernández-Fernández, F. Castaño, J. R. Vázquez de Aldana, and A. Longarte, J. Chem. Phys. 137, 064317 (2012)] is re-visited. The observation of a shift in the pyrrole(+) transient respect to zero delay reference, initially attributed to ultrafast dynamics on the πσ* type state (3s a1 ← π 1a2), is demonstrated to be caused by the existence of pump + probe populated states, along the ionization process. The influence of these resonances in pump-prone ionization experiments, when multi-photon probes are used, and the significance of a proper zero-time reference, is discussed. The possibility of preparing the πσ* state by direct excitation is investigated by collecting 1 + 1 photoelectron spectra, at excitation wavelengths ranging from 255 to 219 nm. No conclusive evidences of ionization through this state are found.

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“…Using photofragment translational spectroscopy (PTS), Blank et al found upon excitation at 193 and 248 nm that the H elimination channel is the main dissociation channel. 1 Later, higher energy-resolution experiments [4][5][6][7][8]15 in the wavelength range 193.3-254.0 nm observed two components in the H product translational energy distributions: a "fast" component with a higher, sharp kinetic energy distribution and a "slow" component with a lower, broad kinetic energy distribution. A picture was proposed as follows: upon the approach of the wavepacket to the conical intersection (CI) between the πσ * and ground states, the wavepacket either evolves to the ground state and results in a statistical dissociation of the hot ground state, leading to nascent H-atoms with lower kinetic energies, or evolves diabatically leading to a direct cleavage of the N-H bond to yield H-atoms with higher kinetic energies.…”

Section: Introductionmentioning

confidence: 99%

Excited state non-adiabatic dynamics of pyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

Neville

Schalk

et al. 2015

The Journal of Chemical Physics

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Coherent polyatomic dynamics studied by femtosecond time-resolved photoelectron spectroscopy: Dissociation of vibrationally excited C S 2 in the 6 s and 4 d Rydberg states J. Chem. Phys. 125, 174314 (2006) 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 (πσ * ) 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 (ππ * ) and B 2 (ππ * ) 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 (πσ * ) 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 (πσ * ) 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 (πσ * ) state. C 2015 AIP Publishing LLC. [http://dx

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UV Photodissociation of Pyrroles: Symmetry and Substituent Effects

Cited by 26 publications

References 28 publications

Ultrafast Excited-State Dynamics of 2,4-Dimethylpyrrole

Ultrafast Excited-State Dynamics of 2,4-Dimethylpyrrole

Revisiting the relaxation dynamics of isolated pyrrole

Excited state non-adiabatic dynamics of pyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

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