Measuring photoionization cross-sections of excited atomic states

A new method of photoionization cross-section measurement based on the observation of saturation in the ion yield as a function of radiation intensity has been proposed. The photoionization cross-sections for the 6²P_1/2 and 6²P_3/2 levels of Rb atoms of the fundamental and second harmonics of ruby laser radiation are measured, with a tunable pulsed dye laser used for excitation. The following values of cross-sections are obtained: (1.7±0.4)·10⁻¹⁷ cm² and (1.5±0.4)·10⁻¹⁷ cm² for the levels 6²P_3/2 and 6²P_1/2, respectively, ionized by radiation of v₂=14403 cm⁻¹, and (1.9±0.5)·10⁻¹⁷ cm² for the 6²P_3/2 level ionized by v₂=28806 cm⁻¹ radiation.     

Theoretical studies on the photoionization cross-sections of solid silver

An alternative expression for photoionization cross-section of atoms or molecules and a dielectric influence function （DIF） in a high-density system proposed recently are used to study the photoionization cross-sections of solid silver. It is suggested that a density turning point （DTP） of a photoionized system may be viewed as the critical point where the photoionization properties of atoms in a real system may have a notable change. The results show that the present theoretical photoionization cross-sections are in good agreement with the experimental results of a silver crystal both in structure and in magnitude.     

Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV

The results of calculations of photoelectric cross-sections for the Kα lines of magnesium at 1254 eV and of aluminum at 1487 eV are presented. All of the subshell cross-sections are given for Z values up to 96. The calculations were carried out relativistically using the single-potential Hartree-Slater atomic model.     

Relative partial photoionization cross-sections and photoelectron branching ratios of ethylene

Relative partial photoionization cross-sections and photoelectron branching ratios of the valence bands (~10–25 eV binding energy) of ethylene are reported over the photon energy ranges 18–100 eV and 21–100 eV, respectively. The four lowest ionization energy bands (1b⁻¹_1u, 1b⁻¹_1g, 3a⁻¹_g, and 1b⁻¹_2u) show monotonic cross-section decreases with photon energy from 33 eV, the 1b⁻¹_1u CC π band showing the least rapid decline. In contrast, the 2b⁻¹_3u and 2a⁻¹_g bands show almost constant cross-sections up to ~50 eV photon energy, followed by similar, although slower, monotonic decreases. This is attributed to the substantial carbon 2s character of the 2b_3u and 2a_g orbitais. The cross-section behaviour of all bands is interpreted with the aid of SCF-LCAO-MO calculations on the neutral molecule using the Gaussian-80 series of programs.     

The energy dependence of the 4d photoionization cross-section of In and Sb

The energy dependence of 4d partial photoionization cross-section for In and Sb has been determined experimentally using the photoemission technique. It exhibits a pronounced Cooper minima and compares favorably with the one-electron Hartree Fock calculation for atomic Xe by Kennedy and Manson.     

Total photoionization cross-sections of Ar and Xe in the energy range of 2.1–6.0 keV

Total photoionization cross-sections of Ar and Xe have been accurately measured in the photon energy region of 2.1–6.0 keV, using a four-electrode ion chamber with monochromatized synchrotron radiation. Experimental data are presented in both graphical and tabular forms and compared with previous data reported in the literatures.     

Determination of photoionization cross-sections of chlorofluoro derivatives of aliphatic hydrocarbons

Absolute photoionization cross-sections of a series of chlorofluoroalkanes have been determined by measuring relative band-intensities in the UP spectra of binary gaseous mixtures. Each mixture (of known composition) contained a chlorofluoroalkane and a standard gas having known partial cross-sections. The experimental results are compared with theoretical data obtained from calculated atomic absolute photoionization cross-sections, adopting the Gelius—Siegbahn model. The agreement between the experimental and theoretical data is satisfactory in reproducing trends and variations.     

Subshell photoionization cross-sections,electron mean free paths and quantitative X-ray photoelectron spectroscopy

Subshell photoionization cross-sections (SPC) for elements of atomic number in the range 3?, z ? 82 have been determined from measurement of relative photoelectron intensities at a photon energy of 1486.6 eV (Al Kα). A correction procedure has been developed which permits such determinations even when sample surfaces are not atomically clean. The results obtained suggest that Scofield's SPC calculations [2] are reasonably reliable for 1s, 2p and 3d subshells but that the present, experimentally derived data are to be preferred for quantitative use. As a result of this work, a rapid method of quantitative surface-constituent analysis, accurate to ± 20%, has also been developed, which is expected to be of value particularly in industrial situations. A semi-empirical method of extracting electron mean free paths from measurements of relative photoelectron intensities is also illustrated.     

Partial photoionization cross-sections and branching ratios of CO from 750 to 304 Å

The absolute values of the partial photoionization cross-sections and branching ratios for producing carbon monoxide ions in their X²Σ⁺, A²Π, B²Σ⁺ and ²Σ⁺(σ2s) states have been obtained as a function of wavelength from the A²Π ionization threshold to 304 Å. Results have been obtained within autoionizing resonances as well as within the photoionization continuum.     

Mid-infrared absorption cross-sections and temperature dependence of CFC-113

The temperature dependence of the infrared absorption cross-sections of CFC-113 (1,1,2-trichlorotrifluoroethane) in a pure vapor phase has been recorded in the 600-1250 cm⁻¹ spectral region using Fourier transform spectroscopy. Spectra at 0.05 cm⁻¹ resolution have been used to derive the integrated band strengths of the five main absorption bands over a range of temperatures from 223 to 283 K. Our results show good agreement with previously published data. The new cross-sections will allow more accurate retrieval of atmospheric CFC-113 concentrations using infrared spectroscopic techniques.     

Intensity dependence of laser-assisted attosecond photoionization spectra

We study experimentally the influence of the intensity of the infrared (IR) probe field on attosecond pulse train (APT) phase measurements performed with the RABITT method (Reconstruction of Attosecond Beating by Interference in Two-Photon Transitions). We find that if a strong IR field is applied, the attosecond pulses will appear to have lower-than-actual chirp rates. We also observe the onset of the streaking regime in the breakdown of the weak-field RABITT conditions. We perform a Fourier-analysis of harmonic and sideband continuum states and show that the mutual phase relation of the harmonics can be extracted from higher Fourier components.     

Energy dependence of topological cross-sections at nal energies

We calculate the normalized cross-sections $\text{σ}{}^1\text{= σ ·}\text{FLUX/LIPS}$ using recent data on topological cross-sections. We confirm the power law behaviour $\text{σ}{}^1\text{= AP}{}^{\mathrm{?n}}{}_{\mathrm{<mtext>lab</mtext>}}$ for energies up to 400 GeV. The exponent n appears to satisfy, approxima tely, the relation n ≈ m ?2 for multiplicities m up to 20.     

The determination of subshell photoionization cross-sections in some solids and gases using photoelectron spectroscopy

Relative subshell photoionization cross-sections have been measured directly for solid samples of Sodium Fluoride and Sodium Chloride by the technique     

Isotopic dependence of fusion cross-sections – linear relationships

A systematic study of isotopic dependence of fusion cross-section is carried out by adding neutrons gradually to N=Z colliding nuclei. We find that fusion barrier position increases and height decreases, both linearly with the increase of N/Z ratio of the compound system. The increase in barrier position is larger compared to decrease in barrier height. In terms of these linear relationships, a parameterized form of fusion cross-sections is given for the neutron-rich colliding nuclei. The fusion cross-sections are also enhanced linearly with the N/Z ratio, and this enhancement is larger for lower incident centre-of-mass energies and independent of the choice of reaction partners. Experimental data and other theoretical studies are called for to verify these results. Received: 27 February 1998 / Revised version: 22 May 1998