ATOMIC AND MOLECULAR DATA AND THEIR APPLICATIONS: 5th International Conference on Atomic and Molecular Data and Their Applications (ICAMDATA)
901(2007); http://dx.doi.org/10.1063/1.2727350View Description Hide Description
We present results from our enhanced statistical equilibrium and time‐step codes for atmospheric modeling. In particular we use these results to illustrate the role of electron‐driven processes in atmospheric phenomena and the sensitivity of the model results to data inputs such as integral cross sections, dissociative recombination rates and chemical reaction rates.
901(2007); http://dx.doi.org/10.1063/1.2727351View Description Hide Description
This article provides an overview of current spectroscopic needs for measurements of atmospheric pollution from Earth satellites. This is now a sizable field of research, with some dozen satellites now performing measurements or being planned or prepared for launch. Measurements of tropospheric chemical constituents, their sources, sinks, transport, and transformation, provide crucial information on tropospheric oxidation chemistry and pollution of the lower atmosphere, and are now being employed to improve global emission inventories of odd nitrogen (NOx) and volatile organic compounds (VOCs).
Pollution measurements include: formaldehyde (HCHO), the m ajor proxy for VOCs; glyoxal (CHOCHO) a recent additional proxy for VOC emissions; NO2, the major proxy for NOx; tropospheric ozone (O3); carbon monoxide (CO); sulfur dioxide (SO2), from volcanoes and from anthropogenic pollution; and enhanced BrO over the polar ice shelves in spring. The needs for improved laboratory Spectroscopic measurements for the various pollutants will be presented.
901(2007); http://dx.doi.org/10.1063/1.2727352View Description Hide Description
This paper presents a brief description of collisional‐radiative model benchmarking experiments performed on tokamak plasmas. The relevance of such experiments for astrophysical research is exemplified with the case of M‐shel iron emission in the soft X‐ray range.
901(2007); http://dx.doi.org/10.1063/1.2727353View Description Hide Description
Across a wide range of wavelengths and encompassing a rich menagerie of astrophysical objects and environments, the need for atomic and molecular data to advance forefront astrophysical research has never been greater. Over the last decade, astronomical discoveries, such as the detection of brown dwarfs and extra‐solar planets, and the observation of new phenomena, such as x‐rays from comets, have created a demand for more and different kinds of data. The next generation of ground‐ and space‐based instruments with greater sensitivities and higher spectroscopic resolution will expand our windows on the Universe, increasing the pressure for atomic and molecular data of higher accuracy and greater completeness. Examples of recent successes as well as future opportunities for research in this area will be discussed.
901(2007); http://dx.doi.org/10.1063/1.2727354View Description Hide Description
Soft X‐ray emission due to charge exchange (CX) between solar wind highly charged ions and atoms and molecules has recently been recognized to occur in a number of solar system objects. Here I present measurements and modelling of CX X‐ray emission around comets, planets, and within the heliosphere (the cavity carved by the solar wind in the interstellar medium). This latter omni‐directionnel emission is due to the interaction between solar wind ions and the flow of interstellar neutrals. It has now been found to be responsible for a large fraction of (if not all) the emission previously attributed to the Local Interstellar Hot Bubble (a 100 parsecs cavity around the Sun supposed to be filled with one million K gas). I also argue for me existence of CX X‐ray emission in galaxies. Because new X‐ray satellites have sufficient sensitivity and spectral resolution to detect the signatures of the CX lines, there is a strong need for theoretical work on CX state‐selective population cross‐sections and ion radiative transition probabilities, their dependence on the interacting species and the collisional energy.
901(2007); http://dx.doi.org/10.1063/1.2727355View Description Hide Description
I present a brief overview of atomic and molecular processes that occur in interstellar clouds exposed to ultraviolet and Xray radiation. I emphasize the crucial role that fundamental atomic and molecular data play in quantitative modelling and interpretation of astronomical observations.
901(2007); http://dx.doi.org/10.1063/1.2727356View Description Hide Description
An emission line of neutral helium λ667.8 nm (21P‐31D) is observed with a set of line of sights which covers an entire poloidal cross section of LHD, a heliotron‐type fusion experimental device. From the observed Zeeman splittings and the well‐known magnetic field structure in the plasma, the emission locations on the line of sight are precisely determined. The distribution of line emissions over the observed poloidal cross section is derived from the results of all the line of sights through a tomographic analysis.
Balmer series lines of neutral hydrogen are measured for the rotating radiation body in the Serpens mode [J. Miyazawa et al., Nucl. Fusion 46, 532 (2006)]. The electron temperature and density are derived from the observed spectra with the help of calculations with the collisional‐radiative (CR) model. The derived electron density is confirmed with the Stark broadening of several lines from n = 7 to 16 levels, where n is the principal quantum number.
We have developed a CR model code for neutral helium based on recently calculated cross section data of electron impact. Six emission lines of neutral helium for the transitions from n = 3 to n = 2 levels are measured for various discharges in LHD and an estimation of the electron temperature and density is attempted from the intensity ratios among three lines, λ667.7 nm (21P‐31D), λ706.5 nm (23P‐33S), and λ728.1 nm (21P‐31S), out of the six lines. Intensities of other three lines, λ388.9 nm (23S‐33P), λ501.6 nm (21S‐31P), and λ587.6 nm (23P‐33D), are calculated with the derived plasma parameters and the agreement with the measured line intensities is found satisfactory.
901(2007); http://dx.doi.org/10.1063/1.2727357View Description Hide Description
High intensity discharge (HID) lamps are low temperature (∼0.5eV), weakly ionized plasmas sustained in a refractory but light transmissive envelope for the purpose of converting electrical power into visible radiation. For commercial applications this conversion must occur with good efficiency and with sufficient spectral content throughout the visible (380–780nm) to permit the light so generated to render colors in a fashion comparable to natural sunlight. These goals are often achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, chemical compounds containing the desired metals, and having higher vapor pressures are used to introduce the material into the basic discharge. Complexing agents which further improve the vapor pressure are used to enhance the amount of metals in the discharge. The metal compound and complexes are usually polyatomic species which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Under the approximation of local thermodynamic equilibrium (LTE) the particles are in equilibrium, but not with the radiation Held. Strong thermal (106K/m) and density gradients are sustained in the discharge. Atomic and molecular radiation produced in the high temperature core transits through colder gas regions before exiting the lamp. In these regions where the complex molecular species exists in an undissociated state, bound‐free transitions can result in energy being effectively converted from light radiation into heat in the mantle. Bound‐bound transitions In Identifiable molecules can result in modification of the spectral output in unpredictable and counter‐intuitive ways. Examples of completing agents and their effect on the spectral output of typical rare‐earth containing HID lamps will be given. The melt composition and the complexing agents themselves may change with time, as chemical reactions in the lamp occur, and their benefit is accordingly altered. Optical absorption and emission data, molecular structure and electron Impact and attachment cross section data on these molecular components is sparse but necessary to understand lamp performance in the lamps re‐ignition phase and during steady state operation. More data are needed.
901(2007); http://dx.doi.org/10.1063/1.2727358View Description Hide Description
Recent research has revealed that it is possible to influence the excitation and dissociation of molecules through the manipulation of electron interactions. Since electrons are ubiquitous in nature electron induced reactions initiate and drive the basic physical‐chemical processes in many areas of science and technology from industrial plasmas to living tissues. Our ability to control electron interactions therefore provides exciting new opportunities that can be exploited by both the research and technological communities. In this brief review we demonstrate the rapid advances being made in this research fields and explore the need for a detailed database of electron‐molecule interactions. We examine the current status of such a database and identify the most important needs in future electron‐molecule research.
901(2007); http://dx.doi.org/10.1063/1.2727359View Description Hide Description
Tungsten is one of very few candidate materials for plasma facing components in future fusion devices. Therefore, investigations have been started at fusion devices and EBITs to provide atomic data for W in fusion plasmas. Usually the influx of impurities is deduced from the intensity of spectral lines from neutrals or ions in a low ionisation state. For this purpose the appropriate ionisation rates and excitation rates have to be known. At the moment, a WI transition (7 S‐7 P) at 400.9 nm is used, but an extension of the method to other lines is under investigation. In the core of present day plasmas ionisation states up to W56+ can be reached and in a reactor states up to around W68+ will be present. In order to extract information on the local W concentrations over the whole plasma radius atomic data (wavelength, excitation, ionisation, recombination) for all the charge states up to the maximum ionisation state are necessary. Similarly, a high sensitivity has to be achieved since the central W concentrations should stay below 10−4. For an unambiguous identification of the transitions EBIT measurements are of great advantage, but due to the lower electron density compared to fusion plasmas, investigations there are indispensable.
901(2007); http://dx.doi.org/10.1063/1.2727360View Description Hide Description
ITER represents the next step towards practical magnetic confinement fusion power. Its primary physics objective is to study plasmas in which the fusion power exceeds the external heating power by a factor of 5 to 10; its technological objectives include the use of superconducting magnets and remote maintenance. We will describe the ITER experiment and then detail the fundamental roles that will be played by atomic physics processes in facilitating the achievement of ITER’s objectives. First, atoms and molecules generated by the interaction of the ITER plasma with surrounding material surfaces will impact and, in some respects, dominate the particle, momentum, and energy balances in both the adjacent and confined, core plasmas. Second, impurity radiation in the edge plasma, either from intrinsic or extrinsic species, will ensure that heat coming out from the core is spread more uniformly over the surrounding material surfaces than it would otherwise. Third, many of the diagnostics used to monitor the dense (ne ∼ 1020 m−3), hot (∼ 1 × 108 K) core plasma leverage off of atomic physics effects.
Improved techniques of measuring accurate electron ‐ molecule cross sections near threshold and over a large angular range901(2007); http://dx.doi.org/10.1063/1.2727361View Description Hide Description
Methods to measure absolute differential elastic and vibrational excitation cross sections using an electron spectrometer with a magnetic angle changer are discussed. Emphasized are the need to by‐pass drifts and to properly correct for the instrumental response function when angle of detection or electron energy are varied. The results are illustrated with cross sections in nitrogen, methane and neopentane. The good agreement of the results with the experimental data from other leading groups (taken mostly without the angle changer) and with some theories indicate that the measurements are reliable. The angle‐integrated data agrees well with the results of electron‐transport experiments. Good agreement with theory is obtained for nitrogen, even in the difficult low‐energy region. Electronic excitation in rare gases is also briefly mentioned.
901(2007); http://dx.doi.org/10.1063/1.2727362View Description Hide Description
We describe a recently developed B‐spline R‐matrix method for electron and photon collisions with atoms and ions. Using non‐orthogonal sets of orbitals to construct the target description and to represent the scattering functions, this implementation of the close‐coupling approach allows us to employ highly correlated target wavefunctions with relatively small configuration expansions. Example results from recent applications of the method for accurate calculations of low‐energy electron scattering from He, Zn, Ne, Ar, Xe, and Fe+ are presented.
Resonant Dissociative Attachment, Vibrational Excitation and Recombination of Molecules and Molecular Ions901(2007); http://dx.doi.org/10.1063/1.2727363View Description Hide Description
In a number of physical environments, electron collisions with molecules and molecular ions initiate and drive the chemistry of the system. In general due to the large mass difference between the electron and target, the cross section is dominated by resonant processes, where the electron can temporarily attach to the molecule and change the forces felt between its atoms for a period of time comparable to a vibrational period. This can lead to resonant vibrational excitation and dissociative attachment, for neutral targets, or dissociative recombination in the case of ions. We outline the basic theory that underlies these processes, and our approach to study them. We then illustrate the method with the study of dissociative recombination for the , , and molecular ions and dissociative attachment of C2H2.
Dissociative Electron Attachment to Thymine: Bond and Site Selectivity in Different Molecular Environments901(2007); http://dx.doi.org/10.1063/1.2727364View Description Hide Description
Low energy electrons effectively decompose thymine via dissociative electron attachment inducing H loss below 3 eV and H− loss above 5 eV. Experiments with partially deuterated or methylated thymine show that the site of dehydrogenation can be precisely controlled by the incident electron energy. Such bond and site selectivity also remains in more complex environments when thymine is a moiety of thymidine (base+sugar unit) and of a thymine cluster embedded in a superfluid helium droplet. Implications for the interpretation of strand breaks in plasmid DNA induced by low energy electrons are discussed.
901(2007); http://dx.doi.org/10.1063/1.2727365View Description Hide Description
The existence of long‐lived states (of the order of microseconds) of the molecular hydrogen anion is discussed both from theoretical and experimental points of view. The history of experimental search for these states is briefly reviewed and a theoretical explanation based on the use of the nonlocal resonance model offered. Final unambiguous confirmation of the existence by means of the accelerator mass spectrometry and mass spectrometry and the measurement of their lifetimes in electrostatic ion‐beam trap is described.
901(2007); http://dx.doi.org/10.1063/1.2727366View Description Hide Description
The recent start‐up of large intense laser facilities such as the Ligne d’Intégration Laser (LIL) or the LULI2000 and the arrival in the near future of the Laser Megajoule (LMJ) gives a great perspective for laboratory astrophysics, dense matter studies and inertial fusion. To make the most of these opportunities, several teams have set up a program which aims at satisfying simulation needs in the fields of Astrophysics, Hot Dense Matter and Inertial Confinement Fusion. A large part of the scientific production in these fields relies upon simulations of complex unsteady hydro flows, coupled to non equilibrium transport and chemical kinetics. As the characteristic time scales of transport may be much shorter than the fluid time scale, implicit numerical methods are often required. Atomics physics data, and in particular equation of states and opacities, are a key and critical ingredients for the simulations done in stellar physics, laboratory astrophysics and in many other fields of astrophysics. We will show the different codes used in the various fields of the project and the different methods used to capture the desired physics. We will also present ODALISC, a new opacity database aiming at providing the community with spectral opacities and numerical tools to use them efficiently in radiation‐hydrodynamics codes.
901(2007); http://dx.doi.org/10.1063/1.2727367View Description Hide Description
Equilibrium rate constants of inelastic processes in dense media have been studied with taking account the quantum corrections to the particle momentum distribution function (PMDF). These corrections arise at high medium pressure and relatively low temperature and can be treated as a manifestation of the time‐energy uncertainty relation for particles colliding elastically at a high rate ν, so that the characteristic energy ℏν becomes comparable with the temperature. The main problem in evaluation of the rate constants of inelastic processes as well as PMDF relates to finding the scattering amplitude out of the energy shell. This problem is resolved within the frame of the approach developed based on the asymptotic representation of the wave function of scattering particles. The explicit solution has been obtained for the problem of vibrational relaxation of diatomic molecules. The specific calculations performed for low temperature atmospheric pressure relaxation of nitrogen result in a reasonable agreement with existing experimental data.
901(2007); http://dx.doi.org/10.1063/1.2727368View Description Hide Description
Future extreme ultraviolet (EUV) lithography will require very high radiation intensities in a narrow wavelength range around 13.5 nm, which is most efficiently emitted as line radiation by highly ionized heavy particles. Currently the most intense EUV sources are based on Xenon or Tin discharges. After having investigated the limits of a hollow cathode triggered Xenon pinch discharge a Laser triggered Tin vacuum spark discharge is favored by Philips Extreme UV.
Plasma and radiation properties of these highly transient discharges will be compared. Besides simple MHD‐models the ADAS software package has been used to generate important atomic and spectral data of the relevant ion stages. To compute excitation and radiation properties, collisional radiative equilibria of individual ion stages are computed. For many lines opacity effects cannot be neglected. The optical depths, however, allow for a treatment based on escape factors. Due to the rapid change of plasma parameters the abundances of the different ionization stages must be computed dynamically. This requires effective ionization and recombination rates, which can also be supplied by ADAS.