Photoelectron angular distribution of simple molecules at 30.4 nm photons

The asymmetry parameter (β) of angular distribution of photoelectrons has been obtained with He(I) (58.4 nm) and He(II) (30.4 nm) resonance radiation for several simple compounds (N₂, O₂, H₂O, CO₂ and CS₂), in order to examine how the β value depends on the excitation energy. It has been found that on going from He(I) to He(II) radiation the energy dependence of β for the nonbonding orbitals of triatomic molecules is similar to that obtained theoretically by Manson for the corresponding atomic p shells. For N₂ it has also been found that there is essentially no difference in β values between two vibrational peaks (υ′= 0 and 1) of the first ionisation band in the He(II) spectrum, whereas in the He(I) spectrum an anomalous variation is observed in the β values between the two peaks as originally indicated by Carlson. These results support the interpretation of the autoionisation mechanism suggested by Mintz and Kuppermann.     

Photoelectron angular distribution measurements of 1,3,5-triazine and 1,3,5,7-cyclooctatetraene

He(I) photoelectron angular distributions of 1,3,5-triazine and 1,3,5,7-cyclooctatetraene were measured. These compounds were found to be typical examples which support the former prediction about the extensibility of the new rule of photoelectron angular distributions presented recently.     

Photoelectron angular distributions and energy spectra of atomic hydrogen in above threshold ionization

Abstract

We extend our model for two-color above threshold ionization to include an infinite number of continua, which are labeled by their angular momenta. Results are presented for the photoelectron spectra and the angular photoelectron distributions.     

线偏振激光场中原子的多光子电离的光电子角分布研究

非微扰量子电动力学的发展使我们可以利用精确的波函数和非微扰的散射理论来研究多光子电离问题.文章作者及其合作者发展了光电子角分布的处理方法,利用复合相位Bessel函数来表征光电子的跃迁几率幅,将光电子的角分布与复合相位Bessel函数直接联系起来.研究发现,复合相位Bessel函数的性质决定了光电子角分布的主要特点及其随激光强度、频率以及光电子能量的演化.该理论不但证实了实验上已经观测到的各种光电子角分布,而且还预言了实验上尚未观测到的光电子角分布,确立了光电子角分布的标度定律.     

线偏振激光场中原子的多光子电离的光电子角分布研究

非微扰量子电动力学的发展使我们可以利用精确的波函数和非微扰的散射理论来研究多光子电离问题.文章作者及其合作者发展了光电子角分布的处理方法,利用复合相位Bessel函数来表征光电子的跃迁几率幅,将光电子的角分布与复合相位Bessel函数直接联系起来.研究发现,复合相位Bessel函数的性质决定了光电子角分布的主要特点及其随激光强度、频率以及光电子能量的演化.该理论不但证实了实验上已经观测到的各种光电子角分布,而且还预言了实验上尚未观测到的光电子角分布,确立了光电子角分布的标度定律.     

Photoelectron angular distributions from gold

Angular distributions of electrons photoemitted from evaporated gold have been measured for 21.2 eV and 40.8 eV photons by varying the acceptance angle of a spherical, electrostatic, electron energy analyzer. The results for primary (unscattered) electrons are shown to be consistent with the three-step model of photoelectron emission.     

Angular distributions of s-subshell electrons in open-shell atoms: 3s photoionization of atomic chlorine

A determination of the angular distribution parameter beta of the atomic chlorine 3s photoelectrons over the photon-energy range from 29 to 70 eV has been carried out using electron spectrometry in conjunction with synchrotron radiation. Our results confirm the basic theoretical predictions that beta, for s-subshell photoionization in open-shell atoms, is in general term and photon-energy dependent, in contrast to closed-shell atoms where beta is always 2 nonrelativistically. However, our measurements of beta for the Cl+ 3s((1,3)P) channels demonstrate that significant details are not handled well by simple Hartree-Fock theory.     

Photoelectron angular distributions from fixed-in-space molecules

Since the fixed-molecule photoelectron angular distribution experiment started in the middle of 1990s, its potential in helping to solve in detail problems in the photoionization dynamics of gas-phase molecules has been recognized. In this review, which is aimed at experimentalists, general expressions of photoelectron angular distributions from fixed-in-space molecules are given for arbitrary polarization, special expressions of them are presented for practical uses, and their applications are explained along our progress on relevant studies with emphasis on the photoionization dynamics exhibited by molecular shape resonances.     

Influence of nondipolar effects on the photoelectron angular distribution upon photoionization of 2p and 3d atomic shells

Relativistic calculations of the angular distribution of photoelectrons upon photoionization of 2p and 3d shells in the range of photoelectron energies from 1 to 10 keV are carried out for unpolarized and linearly polarized radiation. An exact expression for the angular distribution of photoelectrons that takes into account nondipolar terms of the order of O[(kr)²] (k is the photon energy and r is the radius of the ionized shell) is obtained in the case of unpolarized radiation. It is shown that the contribution of the O[(kr)²] terms to the differential cross section can be considerable, reaching 24% at the maximum energy considered. Accounting for such terms in the calculation of the ratio of differential cross sections, which is experimentally measured at a certain geometry of angles in the case of linearly polarized radiation, can change this ratio twofold. The parameters of the angular distribution, which are necessary for the conduction of a quantitative x-ray photoelectron analysis, are given for the 2p _1/2 and 2p _3/2 shells of elements with 11≤Z≤29 and for the 3d _3/2 and 3d _5/2 shells of elements with 30≤Z≤54.     

Photoelectron angular distributions from strong-field coherent electronic excitation

Photoelectron Angular Distributions (PADs) resulting from nonperturbative excitation of potassium atoms using shaped femtosecond laser pulses are presented. We study control exerted by (1) the polarization of an unshaped, i.e., a bandwidth-limited light pulse, (2) shaped linearly polarized light, and (3) a combination of both degrees of freedom, i.e., polarization-shaped laser pulses. A theoretical approach to describe PADs from nonperturbative Resonance Enhanced Multi-Photon Ionization (REMPI) with ultrashort polarization-shaped laser pulses is presented and compared to experimental results. Applications of this technique to the generation and observation of atomic ring currents are discussed.     

Photoelectron angular distributions in resonant multiphonon ionization of atoms

Conclusions It has been demonstrated that photoelectron angular distributions in resonant multiphoton ionization depend critically on the angular momentum quantum numbers of the intermediate state. This should help to interpret the spectra of atoms more complex than alkalies. In addition, information about the matrix elements for the bound-free transition can be obtained which is not available if the angle-integrated ionization cross section is measured. Reliable cross sections for photoionization out of excited atomic states are very important for astrophysics, but so far only a few laboratory data are available. The interpretation of some of these data is not straightforward, however, because of lack of knowledge about the degree of alignment of the atoms in the excited state. This problem can be solved either by optically pumping the atom into only one magnetic sublevel [24] or by measuring the photoelectron angular distribution in addition to the absolute cross section.Sektion Physik der Universitat München, D-8046 Garching, FRG. JILA Visiting Fellow, 1980–1981. Joint Institute for Laboratory Astrophysics, National Bureau of Standards and University of Colorado, Boulder, Colorado 80309. Published in Primenenie Lazerov v Atomnoi, Molekulyarnoi i Yadernoi Fiziki-Trudy II Vsesoyuznoi Shkoly, pp. 12–23, 1981.     

Photoelectron spectroscopy of atomic oxygen using the Elettra synchrotron source

Atomic oxygen has been studied using angle resolved photoelectron spectroscopy (PES) and constant-ionic-state (CIS) measurements using radiation from the Elettra synchrotron as the photon source. Relative partial photoionization cross-sections and angular distributions for the O⁺(⁴S) ← O(³P) and O⁺(²D) ← O(³P) ionizations have been measured as a function of photon energy from threshold (13.6 eV) to 19.0 eV. Comparison of the results obtained with recent experimental work performed at lower resolution reveals a number of differences and comparison with results of recent calculations shows the need for the inclusion of coupling intermediate between the j-j and L-S limits in future calculations of photoionization cross-sections and angular distributions. This work has demonstrated the feasibility of and results to be expected from angle resolved PES and CIS measurements on reactive intermediates at Elettra, a third-generation synchrotron source, and further studies on small molecular radicals are proposed.     

Photoelectron angular distributions from two-photon ionization of atoms near ionization threshold

Photoelectron angular distributions(PADs) from two-photon ionization of atoms in linearly polarized strong laser fields are obtained in accordance with the nonperturbative quantum scattering theory.We also study the influence of laser wavelength on PADs.For two-photon ionization very close to the ionization threshold,most of the ionized electrons are vertically ejected to the laser polarization.PADs from twophoton ionization of atoms are determined by the second order generalized phased Bessel function at which the ponderomotive parameter plays a key role.In terms of dependence of PADs on laser wavelength,corresponding variations for the ponderomotive parameter are demonstrated.     

Photoelectron angular distributions at the ionization of atoms by intense sub-one-cycle laser pulses

The phase sensitivity of the photoelectron angular distributions by intense sub-one-cycle linearly polarized laser pulses has been discussed within the analytic Landau-Dykhne approximation. In both cases of sine and cosine laser pulses most of the electrons are ejected along the polarization axis of the laser field. Nevertheless the electron yield and the electron kinetic energies are much larger for the cosine waveform pulse.     

简单金属Al原子链的磁性

使用密度泛函理论下的第一性原理方法,研究了纳米尺度下简单金属Al原子链的磁性．计算结果显示,一维的Al原子链无论是在线性链还是锯齿形的结构下都有可能表现出磁性,但是这些磁性都是在原子键长被拉伸的情况下才会出现．通过原子轨道相互作用的图像,配合电子状态密度的计算和Stoner判据,解释了一维Al原子链磁性产生的原因． 关键词： 磁性 Al原子链 第一性原理计算     

Photoelectron angular distributions: developments in applications to isolated molecular systems

The last decade has seen photoelectron angular distributions from isolated molecules used for an increasing variety of purposes, including examining details of electron correlation, demonstrating electron diffraction as a structural probe of single molecules, and probing photochemical processes. In this article these developments are reviewed and it is shown that the stage is set for another decade of innovation in which we can expect to see exciting results from pump–probe experiments using the emerging XUV and X-ray free-electron laser sources.     

Photoelectron angular distributions of molecules in bichromatic laser fields of circular polarization

Photoelectron angular distributions (PADs) from above-threshold ionization of O₂ and N₂ molecules irradiated by a bichromatic laser field of circular polarization are studied. The bichromatic laser field is specially modulated such that it can be used to mimic a sequence of one-cycle laser pulses. The PADs are greatly affected by the molecular alignment, the symmetry of the initial electronic distribution, and the carrier-envelope phase of the laser pulses. Generally, the PADs do not show any symmetry, and become symmetric about an axis only when the symmetric axis of laser field coincides with the symmetric axis of molecules. This study shows that the few-cycle laser pulses can be used to steer the photoelectrons and perform the selective ionization of molecules.