Fixed-molecule photoelectron angular distributions

Dill, Dan

doi:10.1063/1.433187

Cited by 255 publications

(189 citation statements)

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“…can be expanded into spherical harmonics [11]. However, due to the nonspherical molecular potential the dipole selection rules do not restrict the expansion as in atoms.…”

Section: Methodsmentioning

confidence: 99%

Analysis of recombination in high-order harmonic generation in molecules

2005

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We show that the dependence of high-order harmonic generation (HHG) on the molecular orientation can be understood within a theoretical treatment that does not involve the strong field of the laser. The results for H2 show excellent agreement with time-dependent strong field calculations for model molecules, and this motivates a prediction for the orientation dependence of HHG from the N2 3σg valence orbital. For both molecules, we find that the polarization of recombination photons is influenced by the molecular orientation. The variations are particularly pronounced for the N2 valence orbital, which can be explained by the presence of atomic p-orbitals.

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“…can be expanded into spherical harmonics [11]. However, due to the nonspherical molecular potential the dipole selection rules do not restrict the expansion as in atoms.…”

Section: Methodsmentioning

confidence: 99%

Analysis of recombination in high-order harmonic generation in molecules

2005

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“…The free electron, e , is a scattering wavefunction expressed as an expansion, with amplitudes and phases, in spherical scattering waves 24,27 . Although TRPES measurements are in principle sensitive to both the electronic and vibrational components of i (t ) through their dependence on d(t ), the angle-averaging implicit in TRPES obscures the details of e .…”

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confidence: 99%

Time-resolved imaging of purely valence-electron dynamics during a chemical reaction

et al. 2011

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Chemical reactions are manifestations of the dynamics of molecular valence electrons and their couplings to atomic motions. Emerging methods in attosecond science can probe purely electronic dynamics in atomic and molecular systems [1][2][3][4][5][6] . By contrast, time-resolved structural-dynamics methods such as electron 7-10 or X-ray diffraction 11 and X-ray absorption 12 yield complementary information about the atomic motions. Time-resolved methods that are directly sensitive to both valence-electron dynamics and atomic motions include photoelectron spectroscopy 13-15 and high-harmonic generation 16,17 : in both cases, this sensitivity derives from the ionization-matrix element 18,19 . Here we demonstrate a time-resolved molecularframe photoelectron-angular-distribution (TRMFPAD) method for imaging the purely valence-electron dynamics during a chemical reaction. Specifically, the TRMFPADs measured during the non-adiabatic photodissociation of carbon disulphide demonstrate how the purely electronic rearrangements of the valence electrons can be projected from inherently coupled electronic-vibrational dynamics. Combined with ongoing efforts in molecular frame alignment 20 and orientation 21,22 , TRMFPADs offer the promise of directly imaging valenceelectron dynamics during molecular processes without involving the use of strong, highly perturbing laser fields 23 . Figure 1 provides a conceptual overview of our method. Carbon disulphide, CS 2 , is a molecule that exhibits all the features generic to polyatomic dynamics: vibrational mode coupling, conical intersections, spin conversion and photodissociation. As such, its non-adiabatic photodissociation reaction CS 2 (X ) Fig. 1, provides an excellent test. In this work we combine experimental measurements with theory to demonstrate how the TRMFPAD images the evolution of the valence-electronic structure of an excited-state wavepacket during the complex, coupled electronnuclear processes inherent to chemical reactions. TRMFPADs probe both nuclear and electronic degrees of freedom through the photoionization matrix elements, d(t ) = + ; e |μ ·E| i (t ) . These matrix elements describe how the initial wavepacket, and its subsequent evolution in time ( i (t )), is projected onto the ionization continuum, consisting of the cation ( + ) and photoelectron ( e ) states, through dipole coupling (μ) with the laser field (E; refs 18,24). In the case of polyatomic molecules, i (t ) and + are composed of coupled electronic and vibrational components (see Supplementary Information). The significance of the TRMFPAD can be understood by considering the intimate relationship between e and the electronic part of i (t ). For example, under the well-known Born (plane-wave) approximation, 1 Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada, 2 Department of Chemistry, University of Copenhagen, Copenhagen DK-2100, Denmark, 3 Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada. *e-mail: alb...

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“…These data can provide much more details on the molecule than PAD from isotropically distributed molecules [193]. Since field-free molecular alignment can only be achieved by an IR laser, PAD from aligned molecules can be measured only at strong-field IR laser facili-ties.…”

Section: Resultsmentioning

confidence: 99%

“…Until recently, however, almost all experimental measurements have been performed from an ensemble of randomly distributed molecules. Thus the rich dynamical structure of photoelectron angular distributions (PADs) for fixed-in-space molecules predicted nearly 30 years ago still remains largely unexplored [193]. Molecular frame photoelectron angular distribution (MF-PAD) has been investigated with X-ray or extreme ultraviolet (XUV) photons if the molecular cation dissociates immediately after the absorption of the photon.…”

Section: Introductionmentioning

confidence: 99%

Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium

Jin

2013

Springer Theses

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In this thesis, we establish the theoretical tools to investigate high-order harmonic generation (HHG) by intense infrared lasers in a gaseous medium. The macroscopic propagation of both the fundamental and the harmonic fields is taken into account by solving Maxwell's wave equations, while the single-atom (or single-molecule) response is obtained by quantitative rescattering theory. The initial spatial mode of the fundamental laser is assumed either a Gaussian or a truncated Bessel beam. On the examples of Ar, N 2 and CO 2 , we demonstrate that the available experimental HHG spectra with isotropic and aligned target media can be accurately reproduced theoretically even though the HHG spectra are sensitive to the experimental conditions. We show that the macroscopic HHG can be expressed as a product of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser and experimental conditions while the latter is the property of the target only. The factorization makes it possible to retrieve the single-atom or single-molecule structure information from experimental HHG spectra. As for the multiple molecular orbital contribution in HHG, it causes the disappearance of the minimum in the HHG spectrum of aligned N 2 with the increase of laser intensity, and the position of minimum in HHG spectrum of aligned CO 2 depending on many factors is also attributed to it, which could explain why the minima observed in different laboratories may differ. For an important application of HHG as ultrashort light source, we show that measured continuous harmonic spectrum of Xe due to the reshaping of the fundamental laser field can be used to produce an isolated attosecond pulse by spectral and spatial filtering in the far field. For on-going application of using HHG to ionize aligned molecules, we present the photoelectron angular distribution from aligned N 2 and CO 2 in the laboratory frame, which can be compared directly with future experiments. demonstrate that the available experimental HHG spectra with isotropic and aligned target media can be accurately reproduced theoretically even though the HHG spectra are sensitive to the experimental conditions. We show that the macroscopic HHG can be expressed as a product of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser and experimental conditions while the latter is the property of the target only. The factorization makes it possible to retrieve the single-atom or single-molecule structure information from experimental HHG spectra. As for the multiple molecular orbital contribution in HHG, it causes the disappearance of the minimum in the HHG spectrum of aligned N 2 with the increase of laser intensity, and the position of minimum in HHG spectrum of aligned CO 2 depending on many factors is also attributed to it, which could explain why the minima observed in different laboratories may differ. For an important application of HHG as ultrashort light source, we show that measured continu...

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Fixed-molecule photoelectron angular distributions

Cited by 255 publications

References 4 publications

Analysis of recombination in high-order harmonic generation in molecules

Analysis of recombination in high-order harmonic generation in molecules

Time-resolved imaging of purely valence-electron dynamics during a chemical reaction

Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium

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