Showing papers on "Photoionization published in 1972"
TL;DR: In this article, the photoelectron spectra of some 40 transition metal compounds have been measured using AlKα(1487 eV) and MgKα (1254 eV), and the chemical shifts of the core electrons and related these results to a calculated charge based on Pauling's electronegativities.
Abstract: The photoelectron spectra of some 40 transition metal compounds have been measured using AlKα(1487 eV) and MgKα(1254 eV) x‐rays. The compounds included both simple salts (halides and chalcogenides) and hexacoordinated complexes (cyano‐ and fluoro‐) of Cr(III), Mn(II, III), Fe(II, III), and Co(III). From these data we have determined the chemical shifts of the core electrons and related these results to a calculated charge based on Pauling's electronegativities. In addition, multiplet splitting has been obtained for photoionization in the 3s shell and is discussed in terms of the exchange interaction between the partially filled 3s and 3d orbitals. To help in this explanation, calculations were made using both (1) Hartree‐Fock solutions of the wavefunctions for free ions and (2) a qualitative evaluation of the behavior of the exchange integral. The value of using x‐ray photoelectron spectroscopy for studying chemical bonding for transition metal compounds is amply illustrated.
575 citations
TL;DR: In this article, the authors examined the effect of photoionization of a small population of neutral atoms (hydrogen or helium) in interplanetary space, and found that even if the density of the newly ionized particles is only a very small fraction of that of the solar wind, these particles can efficiently excite electromagnetic waves by means of a new collective instability.
Abstract: This article examines the consequence of the ionization (e.g., photoionization) of a small population of neutral atoms (hydrogen or helium) in interplanetary space. It is found that, even if the density of the newly ionized particles is only a very small fraction of that of the solar wind, these particles can efficiently excite electromagnetic waves by means of a new collective instability. The instability is driven by an anisotropy in kinetic energy of the newly ionized particles. The typical linear growth rate is γ ≃ (ωin/2½) (υ0⊥/c) where ωin is the plasma frequency of the newly ionized ions, and υ0⊥ is the characteristic speed of the newly ionized ions perpendicular to the ambient magnetic field in the frame of the solar wind.
358 citations
326 citations
TL;DR: Experimental results are given for the photoionization of rubidium vapor using a ruby-laser-pumped dye laser and a doubled ruby laser radiation, and photodissociation of HCl using the Raman-shifted output and the fourth harmonic output of a tunable Nd-glass laser.
Abstract: The general considerations for two-step photoionization of atoms and photodissociation of molecules using tunable laser sources are discussed. Experimental results are given for the (1) photoionization of rubidium vapor using a ruby-laser-pumped dye laser and a doubled ruby laser radiation, and (2) photodissociation of HCl using the Raman-shifted output and the fourth harmonic output of a tunable Nd-glass laser. The possibilities for other laser systems are also discussed.
182 citations
TL;DR: In this article, principal series oscillator strengths and ground-state photoionization cross sections are computed for sodium, potassium, rubidium, and cesium, and the degree of polarization of the photoelectrons is also predicted for each atom.
Abstract: Principal-series oscillator strengths and ground-state photoionization cross sections are computed for sodium, potassium, rubidium, and cesium The degree of polarization of the photoelectrons is also predicted for each atom The core-polarization correction to the dipole transition moment is included in all of the calculations, and the spin-orbit perturbation of valence-p-electron orbitals is included in the calculations of the Rb and Cs oscillator strengths and of all the photoionization cross sections The results are compared with recent measurements
148 citations
TL;DR: In this article, it was shown that the photoionization process of inner-shell electrons by unpolarized radiation leads to an alignment of the ionized atoms by using the nonisotropic angular distribution of the following Auger electrons.
Abstract: It is shown that the photoionization process of inner-shell electrons by unpolarized radiation leads to an alignment of the ionized atoms. From the nonisotropic angular distribution of the following Auger electrons the relative partial photoionization cross sections can be determined.
127 citations
TL;DR: In this paper, the theory of photoionization measurements for a general atomic system is developed in terms of a density matrix which determines the ejected electron and residual ion polarizations as a function of the target atom and incident photon polarization states.
Abstract: The theory of photoionization measurements for a general atomic system is developed in terms of a density matrix which determines the ejected electron and residual ion polarizations as a function of the target atom and incident photon polarization states. Expressions are derived which relate the photoelectron angular distribution and spin polarization parameters to the reduced matrix elements for the photoelectric transition. These expressions incorporate the fine structure of the atomic levels and the complete interaction between the residual ion and the ejected electron. The polarization of the residual ions which are formed in excited states is treated in terms of the subsequently emitted decay radiation.
118 citations
TL;DR: In this paper, the angular distribution of direct photoionization is quite different depending on whether or not the ionization is accompanied by a rotational transition, and the results are compared with available experimental data, which may serve as a basis for extensions to electronic and vibrational autoionization processes.
Abstract: Fano's theory of photoabsorption by ${\mathrm{H}}_{2}$ near the ionization threshold is extended to yield photoelectron angular distributions above as well as between the ionization thresholds for alternative rotational states of the ${\mathrm{H}}_{2}^{+}$ ion. In accordance with recent measurements, the angular distribution of direct photoionization is quite different depending on whether or not the ionization is accompanied by a rotational transition. In the autoionization range between rotational thresholds the angular distribution oscillates along each Rydberg line of the rotational autoionization spectrum, resulting in Beutler-Fano resonance profiles which depend strongly on angle of observation. The results are compared with available experimental data. Angular distributions provide very sensitive tests of the theory. The calculation may serve as a basis for extensions to electronic and vibrational autoionization processes.
89 citations
TL;DR: In this article, it was shown that a major primary photochemical process of CS2 in the vacuum ultraviolet is the reaction, CS2→ lim hνCSA 1Π +S3P2, in apparent violation of the spin conservation rule.
Abstract: It has been shown that a major primary photochemical process of CS2 in the vacuum ultraviolet is the reaction, CS2→ lim hνCSA 1Π +S3P2, in apparent violation of the spin conservation rule. From the threshold energy of incident photons required to produce the fluorescence, CS A 1Π ‐X 1Σ, D0° (SC—S) = 4.463± 0.014 eV or 102.9 ± 0.32 kcal/mole has been obtained in excellent agreement with the value derived previously from the photoionization of CS2. Other related thermochemical data are derived and are compared with those obtained by various methods. The fluorescence excitation spectrum shows peaks corresponding to Rydberg series I and II, indicating that the above reaction is mainly the result of predissociation from Rydberg states. The fluorescence efficiencies became quite small above incident photon energies corresponding to the first ionization potential of CS2. The CS A 1Π fluorescence spectrum produced by the 1236 A line photolysis shows vibrational levels populated up to v′=5. The absorption coeffici...
88 citations
TL;DR: A strong influence of ns2np6 → ns 2np5 ϵd transition on the outer ns subshell photoionization cross section of noble gas atoms is demonstrated in this paper.
86 citations
TL;DR: In this article, a photoionization technique for detection of vibrationally-excited nitrogen (N * 2 ) has been applied to study the quenching of N * 2 by O at 300°K.
TL;DR: In this paper, the gases and cathode of a TEA CO2 laser are irradiated with uv radiation, and the resulting photoionization and photoemission initiate and assist in sustaining a high energy low field strength discharge.
Abstract: The gases and cathode of a TEA CO2 laser are irradiated with uv radiation. The resulting photoionization and photoemission initiate and assist in sustaining a high‐energy low‐field‐strength discharge. Output energy of 50 J/liter at an efficiency of 15% has been obtained in an initial demonstration.
TL;DR: In this article, the information conveyed by relative emission-line intensities in QSO spectra was examined, and it was found that the elemental abundances cannot be estimated with any assurance; but if conventional values are assumed, then certain restrictions may be placed on the ionizing spectra and gas densities.
Abstract: Detailed photoionization calculations are used to examine the information conveyed by relative emission-line intensities in QSO spectra. It is found that the elemental abundances cannot be estimated with any assurance; but if ?conventional' values are assumed, then certain restrictions may be placed on the ionizing spectra and gas densities. In particular, the ratio between radiation density and gas density is determined. Narrow filaments or sheets of ionized gas seem to be indicated; these may be compressed regions behind shock fronts.
TL;DR: In this paper, a new method for the simulation of electrical-breakdown phenomena, and plasma phenomena where both binary electron-neutral-gas-molecule collisions and collective interactions among charged particles are important is presented.
Abstract: This paper presents a new method for the simulation of electrical-breakdown phenomena, and plasma phenomena where both binary electron-neutral-gas-molecule collisions and collective interactions among charged particles are important. Elastic, exciting, and ionizing electron-neutral-gas-molecule collisions are included using a Monte Carlo technique. Electron-ion pairs are released in ionizing collisions. The simulation also includes the release of electron-ion pairs by photoionization. Collective interactions (space-charge effects) are included using a one-dimensional-plasma model which regards the charged particles as charge sheets. Poisson's equation is solved in one dimension based on the positions of the charge sheets to find the accelerating forces on the sheets. The method is used to simulate the growth of electron avalanches and anode- and cathode-directed streamers in nitrogen-filled parallel-plane gaps. Avalanche-simulation results are used to calculate values for the drift velocity and the ionization coefficient in nitrogen. The calculated values for these quantities agree with experimental values over a wide range of $\frac{E}{p}$, the applied electric field divided by the pressure. Velocities for anode- and cathode-directed streamers are calculated based on the streamer-simulation results. The calculated streamer velocities agree with available experimentally measured streamer velocities. The streamer-simulation results also show that photoionization is the essential mechanism for streamer formation and growth.
TL;DR: In this paper, the authors interpreted the data in terms of a model that presumes the magnitude of the rate constant is directly related to the degree of the Franck-Condon factor connecting the molecular neutral and ion.
TL;DR: In this paper, a specially designed mass spectrometer has been used to study the fragment ions following x-ray photoionization of several simple gaseous molecules, containing only first-row elements.
Abstract: A specially designed mass spectrometer has been used to study the fragment ions following x‐ray photoionization of several simple gaseous molecules, containing only first‐row elements. Two photon sources were used: CuLα (930 eV) and CKα (280 eV). The higher‐energy x‐ray source produced initial vacancies primarily in the K shells of the different elements, while the lower‐energy radiation produced ionization entirely in the valence shells. Data were obtained as a function of collection voltage, and relative abundances of the fragment ions were evaluated under conditions of equal collection efficiency. From the shape of the collection efficiency curve the average recoil energies were estimated. The results are briefly discussed in terms of the effect of the KLL Auger processes and multiple ionization.
TL;DR: The angular distribution of electrons in the noble gas photoionization was calculated with many-electron correlations taken into account in the random phase approximation with exchange in this article, where the correlation between the electron correlations was considered.
TL;DR: In this paper, the results of new calculations of partial (i.e., subshell) photoionization cross sections of elements are approximated by analytical approximations to results of previous calculations of the same cross-sections.
Abstract: Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2
TL;DR: In this article, an analysis of Hall-effect and optical measurements showed that Ni, Co, and Mn form relatively deep and compact acceptors in GaAs, with activation energies of 0.20, 0.16, and 0.09 eV, respectively.
Abstract: An analysis of Hall‐effect and optical measurements shows that Ni, Co, and Mn form relatively deep and compact acceptors in GaAs, with activation energies of 0.20, 0.16, and 0.09 eV, respectively. Conduction by free valence‐band holes is augmented at low temperatures by impurity conduction in crystals with heavy doping and strong compensation. The photoabsorption cross section for manganese (which we find to be smaller than hitherto reported) and for cobalt can be viewed as the sum of a Lucovsky‐like δ‐function potential model for photoionization, and smaller but recognizable contributions due to transitions of holes into the V3 ``split‐off'' band, 0.35 eV below the upper valence bands. We have observed the spectral dependence of photoconductivity in these three doped GaAs systems from the intrinsic peak down to the extrinsic threshold.
TL;DR: In this article, photoelectron spectra have been obtained for NO, N2O, CO, CO2 and NH3 over a wide range of photon wavelengths using a dispersed light source.
Abstract: Photoelectron spectra have been obtained for NO, N2O, CO, CO2 and NH3 over a wide range of photon wavelengths using a dispersed light source. The observations cover the wavelength range 584 to 890 A and photoelectron spectra have, in general, been recorded at 5 A intervals in order to survey broad variations in the different photodisintegration processes. Partial photoionization cross sections have been measured for all these gases for processes involving transitions to the ground states and the various excited electronic states of the residual ions; in the case of ammonia, cross sections for dissociative photoionization have also been determined.
TL;DR: In this article, the production of uniform large-volume laser plasmas with electron-ion densities on the order of 1012/cm3 or larger by means of photoionization is investigated.
Abstract: The production of uniform large-volume laser plasmas with electron-ion densities on the order of 1012/cm3or larger by means of photoionization is investigated. An externally applied electric field heats the electron gas to the optimal temperature for excitation of laser levels. Photoionization by intense UV light may take place in a low partial pressure gas of low ionization potential species dispersed throughout the host laser medium, or the laser medium itself may serve as the photoionized species. Both single-photon ionization and two-photon two-step ionization are shown to be applicable.
TL;DR: Oscillator-strength spectra are reported for the formulation of the charge states one to four following N and M ionization in Kr and O and N ionisation in Xe.
TL;DR: In this article, partial photoionization cross sections and angular distribution asymmetry parameter for photoelectrons ejected from helium in the transitions to the n=2 states of the He+ ion are calculated for incident photon energies from just above the threshold to 160.6 eV.
Abstract: The partial photoionization cross sections and the angular distribution asymmetry parameter for photoelectrons ejected from helium in the transitions to the n=2 states of the He+ ion are calculated for incident photon energies from just above the threshold to 160.6 eV. Good agreement is obtained with experiment.
TL;DR: Theoretical and experimental values for the relative band intensities in the Hel-photoelectron spectra of eighteen linear molecules are compared in this article, where qualitative rules concerning band intensity are discussed.