Structural kinetics by time-resolved gas electron diffraction: coherent nuclear dynamics in laser excited spatially anisotropic molecular ensembles

Ischenko, A. A.; Schäfer, Lothar; Ewbank, John D.

doi:10.1016/0022-2860(95)09073-8

Cited by 22 publications

(23 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[4] Specifically, the distribution of molecular transition-dipole-moment vectors of excited molecules at the instant of excitation is determined by a cosine-squared dependence of the absorption strength on the angle between each such vector and the laser polarization vector of a linearly polarized laser pulse. Theoretical calculations of electron diffraction scattering patterns for samples frozen at this initial configuration have been presented for a variety of assumptions for linear [4,5] as well as nonlinear [4] molecules, demonstrating pronounced deviations from isotropic theory. In gas-phase, collisionless samples, this initial anisotropy will decay due to rotation of the individual molecules of the sample on a timescale dictated by the molecular moments of inertia, the direction of the transition dipole in the molecular frame, and the sample rotational temperature, and this timescale has been within the time resolution of several picoseconds employed for many of the already completed UED studies.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Electron Diffraction: Oriented Molecular Structures in Space and Time

Baskin

Zewail

2005

ChemPhysChem

View full text Add to dashboard Cite

The technique of ultrafast electron diffraction allows direct measurement of changes which occur in the molecular structures of isolated molecules upon excitation by femtosecond laser pulses. The vectorial nature of the molecule-radiation interaction also ensures that the orientation of the transient populations created by the laser excitation is not isotropic. Here, we examine the influence on electron diffraction measurements--on the femtosecond and picosecond timescales--of this induced initial anisotropy and subsequent inertial (collision-free) molecular reorientation, accounting for the geometry and dynamics of a laser-induced reaction (dissociation). The orientations of both the residual ground-state population and the excited- or product-state populations evolve in time, with different characteristic rotational dephasing and recurrence times due to differing moments of inertia. This purely orientational evolution imposes a corresponding evolution on the electron scattering pattern, which we show may be similar to evolution due to intrinsic structural changes in the molecule, and thus potentially subject to misinterpretation. The contribution of each internuclear separation is shown to depend on its orientation in the molecular frame relative to the transition dipole for the photoexcitation; thus not only bond lengths, but also bond angles leave a characteristic imprint on the diffraction. Of particular note is the fact that the influence of anisotropy persists at all times, producing distinct differences between the asymptotic "static" diffraction image and the predictions of isotropic diffraction theory.

show abstract

Section: Introductionmentioning

confidence: 99%

Ultrafast Electron Diffraction: Oriented Molecular Structures in Space and Time

Baskin

Zewail

2005

ChemPhysChem

View full text Add to dashboard Cite

show abstract

“…This conclusion is supported by the results of quantum chemical calculations, which show a significant effect of the fluorine atoms. A large number of photodissociation reactions of free molecules were studied (see review articles [17,32,36,38,155]. However, it should be noted that the solution of the inverse scattering problem in the determination of intermediate products of both the photo-excitation and the photo-dissociation in the most of the studies carried out to date was conducted using the theoretical counterpart of the scattering intensity of the electrons in the assumption of an equilibrium distribution of the vibrational and rotational degrees of freedom of the molecules.…”

Section: Structural Dynamics Of Iodine Cleavage Reaction In C 2 H 4 Imentioning

confidence: 99%

“…The introduction of time resolved diffraction techniques [5,6,11,35,36] and the development of the principles of investigation of coherent nuclear motions of isolated molecules also aided the observations of molecular dynamics in condensed phases (please, see, e.g. reviews [37,38]). On the whole, this led to the development of a new way to study matter -coherent structural dynamics [17,31,32,36,39,40] or coherent chemistry [41].…”

Section: Introductionmentioning

confidence: 99%

STRUCTURAL DYNAMICS OF FREE MOLECULES AND CONDENSED STATE OF MATTER. Part II. TRANSIENT STRUCTURES IN CHEMICAL REACTIONS

2017

View full text Add to dashboard Cite

Basic knowledge of mankind so far relates to the description of electrons and atoms in the material in a state of equilibrium, where the behavior changes slowly over time. The electron diffraction with a high temporal and space resolution has opened the possibility of direct observation of the processes occurring in the transient state of the substance (molecular movie). Here it is necessary to provide a temporary resolution of the order of 100 fs, which corresponds to the transition of the system through the energy barrier of the potential surface, which describes the chemical reaction - the process of the breaking and the formation of new bonds between the interacting agents. Thus, the possibility of the investigation of the coherent nuclear dynamics of molecular systems and the condensed matter can be opened. In the past two decades, it has been possible to observe the nuclear motion in the temporal interval corresponding to the period of the nuclear oscillation. The observed coherent changes in the nuclear system at such temporal intervals determine the fundamental shift from the standard kinetics of chemical reactions to the dynamics of the phase trajectory of a single molecule, the molecular quantum state tomography.

show abstract

“…13,14 A new type of GED measurements was developed in 1992 by Schäfer et al 15 and Zewail et al 16 This is the method of pulsed gas electron diffraction ͑pulsed-GED͒, 17,18 in which a laser-based photoelectric pulsed electron beam 19 is introduced in place of the conventional continuous electron beam. 24,25 More recently, we applied pulsed-GED method to investigation of molecules in intense nanosecond laser fields, and succeeded to observe molecular alignment of CS 2 using nanosecond electron pulses, and demonstrated that the pulsed gas electron diffraction method is one of the efficient tools for direct observation of the geometric structure of molecules interacting with intense laser fields. 20 This approach was applied to probe photoisomerization 20,21 and sequential dissociation 22,23 processes of polyatomic molecules.…”

Section: Introductionmentioning

confidence: 99%

Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

Hoshina

Yamanouchi

Ohshima

et al. 2003

The Journal of Chemical Physics

View full text Add to dashboard Cite

A pulsed gas electron diffraction apparatus was developed and applied to investigate an alignment process of molecules in intense laser fields. A two-dimensional ͑2D͒ electron diffraction pattern of jet-cooled CS 2 in intense nanosecond laser fields ͑1064 nm, ϳ0.64 TW/cm 2 , 10 ns͒ was measured using short-pulsed 25 keV electron beam packets ͑ϳ7 ns͒ generated by irradiating a tantalum photocathode with the 4th harmonics of pulsed YAG laser light. The observed anisotropic 2D diffraction pattern was analyzed quantitatively by taking into account the spatio-temporal distributions of the laser pulses, the electron beam packets, and the molecular beam through a numerical simulation of the observed diffraction pattern. The anisotropy of the spatial distribution of molecular axes of CS 2 in the laser polarization direction is accounted for by the effect of the intense laser fields. Considering the spatio-temporal averaging effect, the temporal pulse width of an electron packet required for real-time probing of the alignment process of molecules in intense nanosecond laser fields is discussed. A numerical simulation of temporal and spatial profiles of an electron packet is also performed to examine conditions for generating sub-picosecond ultrashort electron pulse for real-time probing of ultrafast molecular dynamics by the pulsed gas electron diffraction method.

show abstract

Structural kinetics by time-resolved gas electron diffraction: coherent nuclear dynamics in laser excited spatially anisotropic molecular ensembles

Cited by 22 publications

References 47 publications

Ultrafast Electron Diffraction: Oriented Molecular Structures in Space and Time

Ultrafast Electron Diffraction: Oriented Molecular Structures in Space and Time

STRUCTURAL DYNAMICS OF FREE MOLECULES AND CONDENSED STATE OF MATTER. Part II. TRANSIENT STRUCTURES IN CHEMICAL REACTIONS

Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

Contact Info

Product

Resources

About