Femtosecond Time‐Resolved Hydrogen‐Atom Elimination from Photoexcited Pyrrole Molecules

Lippert, H.; Ritze, H.‐H.; Hertel, I. V.; Radloff, W.

doi:10.1002/cphc.200400079

Cited by 114 publications

(181 citation statements)

References 14 publications

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“…Therefore we found no evidence for a fast excitedstate dissociation channel. As a more sensitive method to investigate the possible existence or absence of this pathway, we suggest resonant ionization of H atoms 36 or ethene 37 as the probe step, because otherwise small product yields might remain undetected.…”

Section: Resultsmentioning

confidence: 99%

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

Zierhut

Noller

Schultz

et al. 2005

The Journal of Chemical Physics

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The excited state decay of the hydrocarbon radicals ethyl, C 2 H 5 ; propargyl, C 3 H 3 ; and benzyl, C 7 H 7 was investigated by femtosecond time-resolved photoionization. Radicals were generated by flash pyrolysis of n-propyl nitrite, propargyl bromide, and toluene, respectively. It is shown that the 2 2 AЈ ͑3s͒ Rydberg state of ethyl excited at 250 nm decays with a time constant of 20 fs. No residual signal was observed at longer delay times. For the 3 2 B 1 state of propargyl excited at 255 nm a slower decay with a time constant 50± 10 fs was determined. The 4 2 B 2 state of benzyl excited at 255 nm decays within 150± 30 fs.

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Section: Resultsmentioning

confidence: 99%

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

Zierhut

Noller

Schultz

et al. 2005

The Journal of Chemical Physics

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“…We note that this lifetime is somewhat longer than might be expected, given that a system such as pyrrole exhibits a 1 πσ* lifetime of <100 fs. 65 A relatively long lifetime for the indole 1 πσ* state might also, however, potentially be suggested by the data of Ashfold and co-workers 30 who noted that the shape and intensity of the H atom kinetic energy release spectra they obtained were insensitive to the relative alignment of the photolysis laser polarization, implying an essentially isotropic distribution of fragment recoil velocities. At excitation wavelengths shorter than 263 nm, this includes those fast fragments arising from direct N-H dissociation on the 1 πσ* surface.…”

Section: A Indole At 249 Nmmentioning

confidence: 96%

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Livingstone¹,

Schalk²,

Boguslavskiy³

et al. 2011

The Journal of Chemical Physics

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Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright 1 L a and 1 L b electronic states of 1 ππ* character and spectroscopically dark and dissociative 1 πσ* states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited 1 L a state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived 1 L b state or the 1 πσ* state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the 1 πσ* state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.

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“…The product energy disposals and recoil anisotropies have been rationalised in terms of vibronically induced S 1 S 0 excitation, followed by prompt N-H bond fission -a view confirmed in a number of ultrafast pump-probe studies. [17][18][19] The skeletal motions that promote vibronic coupling with the off-resonant excited electronic state (or states) are orthogonal to the dissociation coordinate and thus act as 'spectators' to the bond fission process, mapping through relatively unchanged into the corresponding vibrational motion in the eventual radical fragment. The formation of v = 0 products implies that at least one of the parent modes lost on N-H bond fission (e.g.…”

Section: -8mentioning

confidence: 99%

UV Photodissociation of Pyrroles: Symmetry and Substituent Effects

et al. 2013

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H (Rydberg) atom photofragment translational spectroscopy and ab initio electronic structure calculations are used to explore ways in which ring substituents affect the photofragmentation dynamics of gas phase pyrroles. S 1 S 0 (*π) excitation in bare pyrrole is electric dipole forbidden, but gains transition probability by vibronic mixing with higher electronic states.The S 1 state is dissociative with respect to N-H bond extension, and the resulting pyrrolyl radicals are formed in a limited number of (non-totally symmetric) vibrational levels (Cronin et al. Phys. Chem. Chem. Phys. 2004, 6, 5031-5041). Introducing -perturbing groups (e.g. an ethyl group in the 2-position, or methyl groups in the 2-and 4-positions) lowers the molecular symmetry (to C s ), renders the S 1 -S 0 transition (weakly) allowed and causes some reduction in N-H bond strength; the radical products are again formed in a select sub-set of the many possible vibrational levels, but all involve in-plane (a) ring-breathing motions as expected (by Franck-Condon arguments) given the changes in equilibrium geometry upon *π excitation. The effects of π-perturbers are explored computationally only. Relative to bare pyrrole, introducing an electron donating group like methoxy (at the 3-or, particularly, the 2-position) is calculated to cause a ~10% reduction in N-H bond strength, while CN substitution (in either position) is predicted to cause a substantial (~3000 cm -1 ) increase in the S 1 -S 0 energy separation but only a modest (~2%) increase in N-H bond strength.3

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Femtosecond Time‐Resolved Hydrogen‐Atom Elimination from Photoexcited Pyrrole Molecules

Cited by 114 publications

References 14 publications

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

UV Photodissociation of Pyrroles: Symmetry and Substituent Effects

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