Narrow Results

Mass selected fullerene ions are exposed to synchrotron radiation in the 17–300 eV energy range. Selected absolute cross-sections for single and multiple ionization as well as fragmentation were measured for ions of C₆₀, C₇₀, C₈₀, C₈₂, and C₈₄. More recently, the first ever experiments with endohedral and fullerene ions have been conducted.

The following sections are included:

• Introduction

• Experimental

• Photochemistry
  • Dimethyl Sulfoxide
  • Substituted Ethylenes
    • Acrylonitrile
    • Vinyl Chloride
  • Oxalyl Chloride
  • Propyne and Allene

• Reactive Scattering
  • Crossed-Beam Reaction Dynamics: Cl + Propane
  • CI + n-Pentane

• Conclusion

• Acknowledgments

• References

The objective of the present study was to better understand the photophysics of explosives and chemical warfare simulants in order to develop better performing analytical tools. Photoionization mass spectra were taken using three optical schemes. The first was resonance-enhanced multiphoton ionization (REMPI) using few-ns duration 248 or 266 nm laser pulses. The second scheme was nonresonant multiphoton ionization (MPI) using 100 fs duration laser pulses at wavelengths between 325 and 795. The third approach was single photon ionization (SPI) using few-ns duration 118 nm laser pulses. For all the molecules investigated, mass spectra resulting exposure to ns-duration 248 or 266 nm laser pulses consisted of only low molecular weight fragments. Using fs-duration laser pulses produced more complicated, potentially analyzable, fragmentation patterns, usually with some parent peak. Single photon ionization gave the best results, with mass spectra consisting of almost only parent peak, except for the case of TATP.

Two methods of laser isotope separation in atomic vapour are compared. The first of them is a well developed Photo-ionization method. The other method is based on isotope-selective excitation of long-living atomic states and subsequent chemical reaction of excited atom with special reagents. It is shown that this method has some principal advantages compared to Photo-ionization method.

Astronomical objects, such as, stars, galaxies, blackhole environments, etc are studied through their spectra produced by various atomic processes in their plasmas. The positions, shifts, and strengths of the spectral lines provide information on physical processes with elements in all ionization states, and various diagnostics for temperature, density, distance, etc of these objects. With presence of a radiative source, such as a star, the astrophysical plasma is dominated by radiative atomic processes such as photoionization, electron-ion recombination, bound-bound transitions or photo-excitations and de-excitations. The relevant atomic parameters, such as photoionization cross sections, electron-ion recombination rate coefficients, oscillator strengths, radiative transition rates, rates for dielectronic satellite lines etc are needed to be highly accurate for precise diagnostics of physical conditions as well as accurate modeling, such as, for opacities of astrophysical plasmas. for opacities of astrophysical plasmas.

This report illustrates detailed features of radiative atomic processes obtained from accurate ab initio methods of the latest developments in theoretical quantum mechanical calculations, especially under the international collaborations known as the Iron Project (IP) and the Opacity Project (OP). These projects aim in accurate study of radiative and collsional atomic processes of all astrophysically abundant atoms and ions, from hydrogen to nickel, and calculate stellar opacities and have resulted in a large number of atomic parameters for photoionization and radiative transition probabilities. The unified method, which is an extension of the OP and the IP, is a self-consistent treatment for the total electron-ion recombination and photoionization. It incorporates both the radiative and the dielectronic recombination processes and provides total recombination rates and level-specific recombination rates for hundreds of levels for a wide range of temperature of an ion. The recombination features are demonstrated. Calculations are carried out using the accurate and powerful R-matrix method in the close-coupling approximation. The relativistic fine structure effects are included in the Breit-Pauli approximation. The atomic data and opacities are available on-line from databases at CDS in France and at the Ohio Supercomputer Center in the USA. Some astrophysical applications of the results of the OP and IP from the Ohio State atomic-astrophysics group are also presented. These same studies, however with different elements, can be extended for bio-medical applications for treatments. This will also be explained with some preliminary findings.

Opacity gives a measure of radiation transport in a medium such that higher or lower opacity indicates more or less attenuation of radiation. As the radiation propagates, opacity is caused by the absorption and emission of radiation by the constituent elements in the medium, such as astrophysical plasmas. It is also affected by photon scatterings. Hence opacity depends mainly on the intrinsic atomic processes, photo-excitation in a bound-bound transition, photoionization in a bound-free transition, and photon-electron scattering. Monochromatic opacity at a particular frequency, κ(ν), is obtained mainly from oscillator strengths (f) and photoionization cross sections (σ_PI). However, the total monochromatic opacity is obtained from summed contributions of all possible transitions from all ionization stages of all elements in the source. Calculation of accurate parameters for such a large number of transitions has been the main problem for obtaining accurate opacities. The overal mean opacity, such as Rosseland mean opacity (κ_R), depends also on the physical conditions, such as temperature and density, elemental abundances and equation of state such as local thermodynaic equilibrium (LTE) of the plasmas. For plasmas under HED (high energy density) conditions, fluid dynamics may be considered for shock waves such as in a supernova explosion.

In this report, I will exemplify the necessity for high precision atomic calculations for the radiative processes of photoexcitation and photoionization in order to resolve some perplexing astrophysical problems relevant to elemental abundances and hence opacities. In particular I will present results on oscillator strengths of Fe XVIII and photoionization cross sections of Fe XVII which are abundant in high temperature plasmas, such as solar corona, and photoionization and recombination of O II which is abundant in low temperature plasmas, such as in a planetary nebula. Sophisticated atomic calculations under the Iron Project are revealing important and dominant features not included in the current opacities. Opacities with these new results are expected to resolve the longstanding problems on abundances in the sun, orion nebula etc.