Imaging the dynamics of gas phase reactions

Ashfold, Michael N. R.; Nahler, N. Hendrik; Orr-Ewing, Andrew J.; Vieuxmaire, Olivier P. J.; Toomes, Rachel L.; Kitsopoulos, Theofanis N.; Garcia, Ivan Anton; Chestakov, Dmitri A.; Wu, Shiou-Min; Parker, David H.

doi:10.1039/b509304j

Cited by 279 publications

(256 citation statements)

References 343 publications

(275 reference statements)

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“…With the traditional velocity mapping technique, 48 an inversion method is needed to process the raw crushed images in order to recover the three-dimensional ͑3D͒ product speed distribution from the two-dimensional ͑2D͒ projection. In contrast with the slice imaging technique, the 3D distribution is directly obtained from the sliced images, 49 without the artificial noise introduced by the transform methods and an enhanced energy resolution in relation to that achieved with the velocity mapping technique. We used delayed pulsed extraction slicing 50 in the single field configuration developed by Kitsopoulos and Papadakis and described in detail in Ref.…”

Section: Methodsmentioning

confidence: 99%

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

Rubio-Lago

Garcı́a-Vela

Arregui

et al. 2009

The Journal of Chemical Physics

110

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The photodissociation of methyl iodide at different wavelengths in the red edge of the A-band ͑286-333 nm͒ has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the methyl fragment in the vibrational ground state ͑ =0͒. The kinetic energy distributions ͑KED͒ of the produced CH 3 ͑ =0͒ fragments show a vibrational structure, both in the I͑ 2 P 3/2 ͒ and I ‫ء‬ ͑ 2 P 1/2 ͒ channels, due to the contribution to the overall process of initial vibrational excitation in the 3 ͑C-I͒ mode of the parent CH 3 I. The structures observed in the KEDs shift toward upper vibrational excited levels of CH 3 I when the photolysis wavelength is increased. The I͑ 2 P 3/2 ͒ / I ‫ء‬ ͑ 2 P 1/2 ͒ branching ratios, photofragment anisotropies, and the contribution of vibrational excitation of the parent CH 3 I are explained in terms of the contribution of the three excited surfaces involved in the photodissociation process, 3 Q 0 , 1 Q 1 , and 3 Q 1 , as well as the probability of nonadiabatic curve crossing 1 Q 1 ← 3 Q 0 . The experimental results are compared with multisurface wave packet calculations carried out using the available ab initio potential energy surfaces, transition moments, and nonadiabatic couplings, employing a reduced dimensionality ͑pseudotriatomic͒ model. A general qualitative good agreement has been found between theory and experiment, the most important discrepancies being in the I͑ 2 P 3/2 ͒ / ͓I͑ 2 P 3/2 ͒ +I ‫ء‬ ͑ 2 P 1/2 ͔͒ branching ratios. Inaccuracies of the available potential energy surfaces are the main reason for the discrepancies.

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Section: Methodsmentioning

confidence: 99%

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

Rubio-Lago

Garcı́a-Vela

Arregui

et al. 2009

The Journal of Chemical Physics

110

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“…When the wave packet is mapped onto the accessible neutral surfaces, the evolution of the resulting different kinetic energy electrons directly reflects the dissociation dynamics of the anion. More recently, velocity map imaging 17,18 used in combination with pump-probe femtosecond laser pulses has demonstrated to be a powerful technique to study the real time dynamics of complex systems. 3,8,[19][20][21] Femtosecond imaging experiments include photoelectron 3,22 and photoionphotoelectron coincidence detection.…”

Section: Introductionmentioning

confidence: 99%

A detailed experimental and theoretical study of the femtosecond A-band photodissociation of CH3I

Nalda

Durá

Garcı́a-Vela

et al. 2008

The Journal of Chemical Physics

100

184

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The real time photodissociation dynamics of CH 3 I from the A band has been studied experimentally and theoretically. Femtosecond pump-probe experiments in combination with velocity map imaging have been carried out to measure the reaction times ͑clocking͒ of the different ͑nonadiabatic͒ channels of this photodissociation reaction yielding ground and spin-orbit excited states of the I fragment and vibrationless and vibrationally excited ͑symmetric stretch and umbrella modes͒ CH 3 fragments. The measured reaction times have been rationalized by means of a wave packet calculation on the available ab initio potential energy surfaces for the system using a reduced dimensionality model. A 40 fs delay time has been found experimentally between the channels yielding vibrationless CH 3 ͑ =0͒ and I͑ 2 P 3/2 ͒ and I * ͑ 2 P 1/2 ͒ that is well reproduced by the calculations. However, the observed reduction in delay time between the I and I * channels when the CH 3 fragment appears with one or two quanta of vibrational excitation in the umbrella mode is not well accounted for by the theoretical model.

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“…VMI is an indispensable experimental tool and has been used in a wide variety of applications. 4 In addition to the measurement of both speed and angular distributions of photofragments, a major advantage of charged-particle imaging is its 4 steradian collection of charged particles and the overall detection efficiency is only limited by the efficiency of the detector. However, under low signal level conditions, the effective efficiency in terms of obtaining a speed or angular distribution is much less.…”

Section: Introductionmentioning

confidence: 99%

Toward real-time charged-particle image reconstruction using polar onion-peeling

Roberts

Nixon

Lecointre

et al. 2009

Review of Scientific Instruments

244

236

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. A method to reconstruct full three-dimensional photofragment distributions from their two-dimensional ͑2D͒ projection onto a detection plane is presented, for processes in which the expanding Newton sphere has cylindrical symmetry around an axis parallel to the projection plane. The method is based on: ͑1͒ onion-peeling in polar coordinates ͓Zhao et al., Rev. Sci. Instrum. 73, 3044 ͑2002͔͒ in which the contribution to the 2D projection from events outside the plane bisecting the Newton sphere are subtracted in polar coordinates at incrementally decreasing radii; and ͑2͒ ideas borrowed from the basis set expansion ͑pBASEX͒ method in polar coordinates ͓Garcia et al., Rev. Sci. Instrum. 75, 4989 ͑2004͔͒, which we use to generate 2D projections at each incremental radius for the subtraction. Our method is as good as the pBASEX method in terms of accuracy, is devoid of centerline noise common to reconstruction methods employing Cartesian coordinates; and it is computationally cheap allowing images to be reconstructed as they are being acquired in a typical imaging experiment.

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Imaging the dynamics of gas phase reactions

Cited by 279 publications

References 343 publications

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

A detailed experimental and theoretical study of the femtosecond A-band photodissociation of CH3I

Toward real-time charged-particle image reconstruction using polar onion-peeling

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