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The National Institute of Standards and Technology (NIST) operates three data centers on atomic spectroscopy. These centers compile three principal quantities characterizing spectral lines: (1) Wavelengths and Energy Levels, (2) Atomic Transition Probabilities, and (3) Line Shape and Shift parameters. (AIP)

In order to test the validity of the [ital LS]-coupling approximation for light elements, the line-intensity ratios of the 3[ital s]-3[ital p] and 3[ital p]-3[ital d] multiplets in C II through FV and C II through Ne VI, respectively, have been investigated experimentally with emission sources. Also, calculations with multiconfiguration Dirac-Fock wave functions have been performed. Within the errors of the experimental procedure, no significant violations of the [ital LS]-coupling approximation were found for the lines of the 3[ital s]-3[ital p] and 3[ital p]-3[ital d] multiplets in C II through F V . However, in the case of Ne VI, small deviations of measured intensities from those obtained by applying the [ital LS]-coupling approximation were observed.

Accurate atomic collision and structure data are an essential ingredient for a wide range of research fields as well as for major technological applications. Areas from laboratory physics to quantum processing, from plasma research applications in nuclear fusion to lighting research, as well as astrophysics and cosmology, depend critically on such data. But many data still exhibit inconsistencies and inaccuracies, so that significant efforts are continuing to improve the data quality. Additionally, a substantial body of much-needed data is absent from the published literature and from databases. Appreciable progress is being made, aided by greatly improved, or even entirely new, laboratory equipment and by vastly expanded computer power, which has made possible the development of greatly refined atomic structure codes. Thus in recent years, atomic data have not only become more accurate, but the body of data has also greatly increased, highly ionized species and complex heavy atoms have been addressed, fully relativistic treatments have been developed, and new energy and frequency ranges have been explored. This special issue focuses on many of these new sophisticated theoretical and experimental approaches that have made high precision atomic physics a reality. On the experimental side, several contributions cover the area of highly charged ions, where accurate measurements have become possible mainly due to the availability of electron beam ion traps (EBITs) and the utilization of storage rings. Studies of QED effects in Li-like ions, determinations of atomic lifetimes and precision wavelength measurements of highly charged ions are discussed. Furthermore, two contributions illustrate the extremely high precision of spectroscopic measurements for heavy ions and atoms, and two fundamental investigations address a new search for the electric dipole moment of the electron and measurements of the anapole moment in Fr and Rb. On the theoretical side, the contributions demonstrate that new, expanded and refined atomic structure and electron-impact collision codes are successfully applied to complex atomic systems, such as highly charged ions and heavy atoms, using increasingly full relativistic treatments.

Two data centers at the National Institute of Standards and Technology (NIST) are engaged in the critical compilation of atomic spectroscopic data including those for highly ionized atoms-- the Atomic Energy Levels Data Center and the Data Center on Atomic Transition Probabilities. Several major compilations have been recently completed, centered on the iron-group elements.

The branching ratio technique for radiometric calibrations in the vacuum ultraviolet is reviewed. Some examples of recent applications are given, and extensions of the method to enlarge its range are discussed. This method is based on the availability of transition probability data for pairs of suitable atomic transitions, and its success depends critically on the quality of these data; furthermore, the ratio of the two transition probabilities should not be extremely large or small. Early uses of the branching ratio technique often suffered from rather inaccurate transition probability data. It is shown that with the recent arrival of powerful comprehensive atomic structure calculations and some very accurate new experimental emission and lifetime data, the availability of highly accurate transition probability data has greatly increased. Especially for helium-, lithium-, beryllium-, boron-, and carbonlike ions many available data are now of an accuracy that permits applications of this technique that are precise to with 5–10%.

For the first time since its inaugural meeting in Lund in 1983, the triennial international conference on Atomic Spectroscopy and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS) returned to Lund, Sweden. Lund has been a home to atomic spectroscopy since the time of Janne Rydberg, and included the pioneering work in laboratory and solar spectroscopy of Bengt Edlen, who presented the initial ASOS talk in 1983. The ninth ASOS was hosted by the Lund Observatory and the Physics Department of Lund University during from 8 to 10 August 2007 and was attended by nearly 100 registrants. An encouraging sign for the field was the number of young researchers in attendance. This volume contains the submitted contributions from the poster presentations of the conference, and represents approximately forty percent of the presented posters. A complementary volume of Physica Scripta provides the written transactions of the ASOS9 invited presentations. With these two volumes the character of ASOS9 is more fully evident, and they serve as a review of the state of atomic spectroscopy for spectrum analysis and the determination of oscillator strengths and their applications. The goal of ASOS is to be a forum for atomic spectroscopy where both the providers and users of atomic data, which includes wavelengths, energy levels, lifetimes, oscillator strengths, and line shape parameters, can meet to discuss recent advances in experimental and theoretical techniques and their application to understanding the physical processes that are responsible for producing observed spectra. The applications mainly originate from the fields of astrophysics and plasma physics, the latter including fusion energy and lighting research. As a part of ASOS9 we were honored to celebrate the retirement of Professor Sveneric Johansson. At a special session on the spectroscopy of iron, which was conducted in his honor, he presented his insights into the Fe II term system and his most recent work with astrophysical applications. Professor Johansson was also honored with heart-felt acknowledgements at the conference dinner on an unusually warm Lund summer evening. Prior to the publication of these proceedings, we were extremely saddened to learn of Sveneric's passing on 10 October 2008. Sveneric Johansson, a founding father of the ASOS conference series, was widely known for his pioneering work on the atomic structure of heavy elements as a well as for his leadership of the international FERRUM Project, which successfully determined a definitive set of spectroscopic data for Fe II. His knowledge of spectroscopy, leadership qualities, and friendship will be dearly missed. Acknowledgements: The spirit of ASOS has been maintained by the dedication of the organizing committees who have kept a tight focus on the nature of the conference, yet allowed for the incorporation of new areas of research in the field. The International Program Committee for ASOS9 is to be commended for their efforts in providing an interesting program. They have also served as the primary source of referees, which along with other referees have performed a valuable service. Many thanks must be given to the local organizing committee, who made the return of ASOS to Lund a memorable experience through both the many opportunities for social gatherings during the conference and a post-conference outing through Skane. We would also like to express our appreciation to the Royal Swedish Academy of Sciences, the Royal Physiographic Society in Lund, the Wenner-Gren Foundation, and the Lund Laser Centre and Department of Physics for their generous support in making ASOS9 possible. Glenn M Wahlgren Wolfgang L Wiese Peter Beiersdorfer Editors

These proceedings contain the written versions of invited talks presented at the Sixth International Colloquium on Atomic Spectra and Oscillator Strengths (ASOS 6), which was held at the University of Victoria, British Columbia, Canada, from August 9 through August 13, 1998. A separate volume, to be published as a technical report of the University of Victoria, will contain the extended abstracts of the poster papers given at this conference. The colloquium was attended by about 80 registered participants, and twenty-four invited talks and 60 contributed papers (mostly as posters) were presented. This meeting was smaller than the last two of this conference series at Meudon, France, in 1995 and at Gaithersburg, MD USA, in 1992, mainly because many Eastern European scientists, usually a strong presence, were unable to come. The invited talks covered seven main subject areas: laboratory studies of complex spectra and measurements of oscillator strengths; advances in atomic structure theory; precision calculations and experiments on neutral helium; astrophysical spectroscopy, both with ground-based observations as well as with the on-going and upcoming space missions; scientific and technological utilizations of atomic and ionic spectra, mainly for diagnostics and modeling purposes; and reviews of new and extended spectroscopic databases. This series of triennial international conferences started fifteen years ago with a meeting at Lund University, Sweden. It has considerably changed and evolved since then, featuring major new trends in spectroscopic research as well as covering the ever larger and more demanding applications and needs of spectroscopic data users. But its main objective, to provide a forum for discussions and a dialogue between data producers and users, has remained essentially unchanged. This international colloquium series has indeed been quite successful at this goal, and has attracted changing groups of producers and users as new topics and new applications have come to the forefront. At the Victoria meeting, some of the 'hot' topics have been the ultra-high precision spectroscopy of neutral helium, further advances in sophisticated atomic structure theory, the rapid shift of laboratory work to the powerful Fourier Transform Spectroscopy, new space astronomy applications which are increasingly shifting to the VUV and X-ray regions; new high-technology applications; and vastly expanded spectroscopic databases utilizing the convenience of the internet. The two sessions on 'precision spectroscopy of helium' and 'laboratory spectroscopy of complex spectra' were dedicated to William C Martin of the National Institute of Standards and Technology, Gaithersburg, MD, USA (formerly the National Bureau of Standards) on the occasion of his retirement after 41 years of outstanding service to atomic spectroscopy. Bill has led the Atomic Spectroscopy group at NIST/NBS for the last 36 years and has made major contributions to the subjects of the two above named sessions. His work on the helium spectrum and his data volume on the energy levels of rare-earth elements are sure to have major impact on atomic spectroscopy for a long time to come. Furthermore, he has contributed greatly to the design and development of the new NIST atomic spectra database on the Internet. Finally, we like to emphasize that no less than half the invited speakers are from a new generation of producers and users, and we therefore feel confident about the future of this International Colloquium which is scheduled to take place again in 2001 at the Queen's University in Belfast. Acknowledgements: We would like to thank the members of the International Program and the Organizing Committees for their many valuable suggestions and assistance in the preparation of the conference. We especially want to express our deep gratitude to Professor Jeremy Tatum of the University of Victoria, who has tirelessly and imaginatively responded to and accommodated numerous special requests of conference participants and has thus contributed greatly to the smooth running of the meeting. We also gratefully acknowledge the competent assistance of Patricia McGuire and the University of Victoria conference management team for their expert organizational skills. We thank Arlene Robey, Sharon Reeves and Suzanne Sullivan, all of the National Institute of Standards and Technology (NIST), Gaithersburg, MD for their competent assistance in editing these proceedings. Finally we thank the sponsors for their financial support of the conference.

The new Atomic Spectra Database (ASD), Version 2.0, of the National Institute of Standards and Technology (NIST) contains significantly more data and covers a wider range of atomic and ionic transitions and energy levels than earlier versions. All data are integrated. It also has a new user interface and search engine. ASD contains spectral reference data which have been critically evaluated and compiled by NIST. Version 2.0 contains data on 900 spectra, with about 70000 energy levels and 91000 lines ranging from about 1 Angstrom to 200 micrometers, roughly half of which have transition probabilities with estimated uncertainties. References to the NIST compilations and original data sources are listed in the ASD bibliography. A detailed "Help" file serves as a user's manual, and full search and filter capabilities are provided.

Branching fractions for electric dipole transitions from 2p4 3p,2p4 3d, and 2p4 4s upper levels in singly ionized neon atoms excited in a high-current hollow-cathode lamp were measured. Transition probabilities for many weak intercombination lines were determined for the first time to the authors’ knowledge. The measurements were carried out with two different techniques to minimize the effect of systematic errors, first in an experiment with a 2-m grating monochromator and then with a Fourier transform spectrometer. The uncertainty of the branching fraction data is 4%(1σ) for lines corresponding to LS-allowed transitions and 30%(1σ) for weak intercombination lines. For 14 upper levels complete sets of transitions could be measured that enabled us to determine absolute transition probabilities when lifetime data for the upper levels were available.

Calculations of the Stark broadening of hydrogen lines treat the radiating atoms and the perturbing ions as quasistatic. The present experiment represents an attempt to determine whether the possible breakdown of this approximation near the center of the line can account, at least partially, for the existing discrepancies between theoretical and experimental profiles in the core of the Balmer lines. The central regions of ${H}_{\ensuremath{\alpha}}$, ${H}_{\ensuremath{\beta}}$, ${H}_{\ensuremath{\gamma}}$, and ${H}_{\ensuremath{\delta}}$ profiles have been measured in a wall-stabilized arc over a range of atom-ion relative velocities by varying the atom-ion reduced mass. The cores of all four lines exhibit a significant dependence on the reduced mass. With increasing reduced mass, the experimental profiles gradually show more structure, but still less than the theories predict. Extrapolation of the results for ${H}_{\ensuremath{\alpha}}$ and ${H}_{\ensuremath{\beta}}$ to infinite reduced mass, i.e., to the static case, gives results that agree quite well with recent calculations.

We have measured the profiles of plasma-broadened and slightly red- or blue-shifted spectral lines of neutral argon and nitrogen in a wall-stabilized arc and have performed a detailed line-shape analysis with a computerized data acquisition and processing system. According to Stark broadening theory, isolated lines of neutral atoms in dense plasmas are mostly broadened by electron impact resulting in symmetrical Lorentzian profiles, and are also broadened by the plasma ions, which produce a small additional contribution to the width as well as asymmetries in the line profile. As in two earlier experimental studies, we have utilized this difference in symmetries to study the effects of ion broadening. In this paper we have extended our work to some unusual cases where lines exhibit relatively rare ``blue'' shifts and where we study spectral transitions which are appreciably broadened because they originate from high-lying atomic levels. Our results are again in close agreement with the quasistatic theory of ion broadening which predicts that the asymmetry pattern has a characteristic minimum and maximum near the central part of the lines, but this pattern is reversed for the blue-shifted lines. We have also utilized the asymmetries for a check on plasma homogene- ity. By deliberately including nonhomogeneous areas of emission into the line of sight, we found drastic, readily observable distortions in the asymmetry patterns.

A systematic study of the influence of cascades on heavy-ion beam-foil decay curves has been made. Using theoretical data for the lifetimes and initial populations of excited states, decay curves simulating beam-foil excitation conditions have been constructed for the resonance transition of three ions in the copper isoelectronic sequence. Various models for the initial population distribution were tested by comparison with a detailed beam-foil decay curve available for Krviii. We found that customary exponential-fitting methods were not able to extract the primary lifetimes from the simulated curves used in constructing them, although the replenishment ratios were close to zero. General implications of this subtle masking of the primary lifetime by numerous cascades for the accuracy of experimental beam-foil data are discussed, especially for $\ensuremath{\Delta}n=0$ transitions in heavy ions.

Determinations of the atomic transition probabilities for prominent spectral lines of Ar I and II are classical cases for testing the capabilities of the emission spectroscopy method. Despite numerous attempts to measure these data accurately, differences of about 30–40% remain in the numerical results, and the available material actually suggests two scales for the transition probabilities, differing by about 30%, as has been pointed out repeatedly. A critical analysis of all emission experiments undertaken in this study is able to remove these differences satisfactorily. A single transition probability value with an error estimated of only ±5% is established for a typical Ar I transition; however, discrepancies for the Ar II data are not removed and remain as a challenge to future experiments.

A critical review of all available data on the Stark widths and shifts for lines of non‐hydrogenic ionized spectra has been carried out. The relevant literature compiled by the NBS Data Center on Atomic Line Shapes and Shifts was critically evaluated, and from this evaluation 54 papers were found to satisfy all requirements and thus selected for this review. The most important factors determining the quality of plasma sources, diagnostic techniques, and line profile and shift determinations are discussed in detail in the first part of this review. In the second part the data tables containing the selected experimental Stark broadening parameters are presented. The data are arranged according to spectra and elements, and these are presented in alphabetical order. The accuracy of the experimental data is estimated on the basis of guidelines developed during the review, and comparisons with theoretical results are made whenever possible.

Wavelengths, energy levels, level classifications, oscillator strengths, and radiative transition probabilities for the nickel ions Ni IX to Ni XXVIII are critically reviewed and tabulated. Grotrian diagrams are also presented to provide graphical overviews. The literature has been surveyed to mid-1986.

The branching-ratio technique for calibrations in the VUV is reviewed in detail. The basic method is described, followed by extensions and applications. Lists of transitions suitable for the technique are given for H-, He-, Li-, and Be-like ions, along with pertinent data for their application.

Regularities and similarities in plasma broadened line widths have been studied by a comprehensive analysis of existing experimental data. Regularities are expected on the basis of general atomic structure considerations, and should be evident for spectral series, for corresponding transitions in homologous atoms and in isoelectronic sequences. Furthermore, similarities of line widths are expected for multiplets, supermultiplets and, to a lesser degree, for transition arrays. A comprehensive examination of literature data has been undertaken, which shows generally a close adherence of the measured data to the expected regularities. A few notable exceptions are also given.

The decay of the $4s4p^{1}P_{1}^{o}$ level in Krvii following beam-foil excitation has been simulated using theoretical initial-state populations and calculated transition probabilities. It was found that the decay curve was substantially influenced by cascading from higher levels and that such cascades dominate the decay in the region beyond three times the lifetime of the $4s4p^{1}P_{1}^{o}$ level. The simulation is in good agreement with an experimental decay curve at short decay times, but is unable to reproduce the long-time behavior of the experimental data. However, recent spectroscopic evidence indicates that line blending is responsible for this aspect. Complications due to core-excited states and other complex cascade mechanisms are discussed.

Based on comparisons with recent theoretical data, it is shown that the effective Gaunt factor for Δn = 0 transitions in alkali-like ions is within 25% of unity in most cases and is a slowly varying function of energy. A more complex energy dependence is noted for some non-alkali-like spectra, and especially for Δn ≠ 0 excitations. A method for the approximation of important correlation effects in the target is discussed for transitions of the type ns21S-nsnp 1P0.

We have measured the profiles of plasma-broadened, slightly red-shifted spectral lines of neutral argon with a wall-stabilized arc and performed a detailed line-shape analysis with a computerized data acquisition and processing system. According to Stark broadening theory, isolated lines of neutral atoms in dense plasmas are broadened mostly by electron impact, which results in symmetric Lorentzian profiles. An additional small broadening contribution, which is asymmetric in nature, is due to the plasma ions. This difference in symmetries provides the possibility of separating ion broadening effects from the electron broadening. In full agreement with the quasistatic theory of ion broadening, our experiment shows asymmetry patterns with characteristic minima and maxima near the central part of the lines. While the positions of these extrema---as well as the zero crossing point---stay essentially constant for all lines when compared on a reduced wavelength scale, the amplitudes of the extrema vary from line to line. Measurements of the amplitudes thus allow, by comparison with theoretical asymmetry patterns, the determination of ion broadening parameters.

Atomic transition probabilities for about 1500 allowed spectral lines of the elements scandium and titanium through all stages of ionization have been critically evaluated and compiled. All available literature sources have been utilized. The data are presented in separable tables for each element and stage of ionization and are arranged according to multiplets and, when appropriate, also to transition arrays and increasing quantum numbers. For each line the transition probability for spontaneous emission, the absorption oscillator strength, and the line strength are given along with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels (when available) of the upper and lower atomic states. In addition the estimated accuracy and the literature reference is indicated. In short introduction, which precede the tables for each spectrum, the main justifications for the choice of the adopted data and for the accuracy rating are discussed. A general introduction contains s...

Relative transition probabilities of 13 transitions between the 3p54s and 3p54p configurations in Ar I have been measured in emission with a wall-stabilized arc. These data have been combined to yield relative lifetimes which are compared with recent direct lifetime measurements. An important consideration in our experiment was to minimize effects of radiation imprisonment since this effect may have played an important role in lifetime measurements by other methods. Our results agree well with most previously published lifetime data and emission measurements.

A new critical review of the available experimental data on the Stark widths and shifts for lines of non‐hydrogenic ionized spectra has been carried out which covers the period from 1976 to the present and represents a continuation of an earlier critical review. The relevant literature, compiled by the NBS Data Center on Atomic Lines Shapes and Shifts as well as by the present authors, was critically evaluated, and data tables containing the selected experimental Stark broadening parameters have been assembled. The data are arranged according to spectra and elements and these are presented in alphabetical order. The accuracy of the experimental data is estimated on the basis of guidelines developed during the previous review. Comparisons with theoretical results are made whenever possible since the comparison with theory has often been a principal motivation for the experiments.

We have measured detailed profiles of plasma-broadened neutral-carbon lines, utilizing a wall-stabilized arc source and a specially designed data acquisition and processing system. We analyzed the lines in terms of symmetric Lorentzian profiles in order to isolate the deviations due to asymmetries and found regular patterns of an antisymmetric nature around the line centers. The asymmetry patterns have a common shape with a minimum, maximum, and zero crossing at the same points on a reduced wavelength scale, but they vary widely in their amplitudes. These findings are in excellent qualitative agreement with the quasistatic theory of ion broadening due to the quadratic Stark effect. A comparison and match of experimental and theoretical amplitudes has thus been used to determine the ion broadening parameters of these lines, which are in satisfactory agreement with directly calculated values.

A number of newly established or significantly improved systematic trends of atomic oscillator strengths in isoelectronic sequences and spectral series are presented. For most of these trends, beam-foil experiments have played a prominent role in supplying critically needed points. Of particular interest are the changes in several transitions of the Be and C sequences brought about by improved beam-foil results and more refined theoretical calculations. Also of significance are newly detected trends in the Li and Al isoelectronic sequences. An example will be given where the analysis of the ƒ- value dependence along a sequence, coupled with an understanding of the changes in the energy level structure, points out areas where future beam-foil experiments would be desirable in clearing up discrepancies. The n ∗3 dependence of oscillator strengths for perturbed series will be illustrated with another interesting example.

Transition probabilities for allowed lines of Ba I and II, based on a critical evaluation of available literature sources, are presented in order of increasing quantum numbers.

The Stark-broadened profiles of the Balmer lines ${\mathrm{H}}_{\ensuremath{\alpha}}$, ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{H}}_{\ensuremath{\delta}}$, have been measured in a high-current, wall-stabilized arc operated in hydrogen. Temperatures and electron densities have been determined with a plasma model assuming partial local thermodynamic equilibrium (LTE), after a detailed plasma analysis revealed small deviations from complete LTE. The temperatures have been determined from line-to-continuum intensity ratios using ${\mathrm{H}}_{\ensuremath{\beta}}$ and continuum points in the near uv, and the electron densities were derived from absolute intensity measurements. The investigations cover the range of electron densities between 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ and ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures between 0.9 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$ and 1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$ K. Extensive comparisons with recent Stark-broadening theories and other experiments have been undertaken with the following principal results: The most pronounced differences between this experiment and theory occur in and near the line centers, where the measured profiles show systematically less structure than the calculations predict. Comparisons of the calculated and precisely measured ratios between the \textonehalf{}, \textonequarter{}, and $\frac{1}{8}$ widths within each line show that the recent theories are internally consistent within 6% for ${\mathrm{H}}_{\ensuremath{\beta}}$ and ${\mathrm{H}}_{\ensuremath{\gamma}}$, whereas for ${\mathrm{H}}_{\ensuremath{\alpha}}$ inconsistencies of order 25% occur. Similar inconsistencies, somewhat larger respectively, are found for the theoretical values of the half-width ratios between different Balmer lines. For the most important line ${\mathrm{H}}_{\ensuremath{\beta}}$, the measured half-widths agree within 7% with the calculated values. The total experimental error in this comparison, which originates predominantly in the electron-density measurement, is estimated not to exceed 6%. Very reproducible asymmetries and red shifts are observed for ${\mathrm{H}}_{\ensuremath{\beta}}$ and ${\mathrm{H}}_{\ensuremath{\gamma}}$. Somewhat smaller red shifts are also obtained for ${\mathrm{H}}_{\ensuremath{\alpha}}$. The shifts are approximately linear functions of the electron density. Comparisons with other experimental data show appreciable scatter between the various results. We estimate that for the most-often-studied line ${\mathrm{H}}_{\ensuremath{\beta}}$ the uncertainties in the theoretical Stark widths are of the order of (5-7)% for the range of our experiment.

A mechanical spectrograph shutter for exposure times down to 5×10=8 sec with a system for synchronization is described and its performance discussed. In contrast to Kerr‐cell shutters most of the incident light is transmitted, which is of considerable importance in extending the range of photographic spectroscopy to studies of very brief transients.

We have determined the transition probabilities for 23 lines of the Ar i 4s-5p array by emission spectroscopy utilizing a wall-stabilized arc. The seven remaining lines of this transition array were either very weak or overlapped strongly with other lines so that they could not be reliably measured. We placed our relative data on an absolute scale by applying the result of a recent critical analysis for the prominent 4s-5p line at 430.01 nm.

Wavelengths for about 47,000 spectral lines of atoms and atomic ions, as well as transition probabilities A for about 5000 lines, are tabulated. The data were selected in such a way as to include the prominent lines over a wide spectral region. Part I contains wavelengths of lines of neutral through quadruply ionized atoms in the range 40 to 40,000 A. This information is presented in two different ways: (1)separate line lists grouped according to chemical element and further subdivided according to stage of ionization; and (2) a general table of wavelengths ordered numerically, with relative intensity, chemical element, and stage of ionization indicated for each line. Part II contains transition probability data for atoms in various stages of ionization, with emphasis on the neutral and singly ionized species. This table is arranged according to the chemical element and is further subdivided according to stage of ionization. Estimates of the accuracies of the A-values are provided. Wavelengths, energy levels, and statistical weights serve to identify the lines and to provide useful data for plasma spectroscopy applications. (Author)

The Commission has, since its inception, been devoted to the continually increasing needs of astronomy and astrophysics for reliable atomic and molecular data a) for diagnostic interpretation of astronomical observations, and b) for support of theoretical modelling of astrophysical situations. At the 1985 Delhi General Assembly, the Commission reviewed the scope of its subject matter, and considered whether it should be extended to include higher energy physical processes than are commonly treated by atomic and molecular data. It was concluded that there was no strong demand for this change, which, if implemented, would make the work of the Commission too diffuse. The appropriateness of the past working group structure was also carefully reviewed in the light of contemporary needs. The following working groups, which have evolved from those of past years, together with their chairmen was approved: 1: Atomic Spectra and Wavelength Standards (excluding primary standards): W.C. Martin 2: Atomic Transition Probabilities: W.L Wiese 3: Collision Processes: A. Dalgarno 4: Line Broadening: N. Feautrier 5: Molecular Structure and Transition Data: W.H. Parkinson

The astronomer’s requirments for atomic data are so massive that it is not easy to approach this subject in a way that sound responsible to someone who is not thoroughly familiar with the situation. the simple truth is that there is urgent needed in some domain of astronomy. This comes about partly becuase of the high temperatures and very long path legths in astronomical objects which can make tham extremely powerful light sources. More generally, we can say conditions in the astronomer’s violent universe manage to render large volumes of phase space available to the atoms which occupy it.

The atomic transition probabilities and radiative lifetimes of neutral argon have been the subject of numerous experiments and calculations, but the results exhibit many discrepancies and inconsistencies. We present a unified set of atomic transition probabilities, which is consistent with essentially all recent results, albeit sometimes only after critical reanalysis. The data consistency and scale confirmation has been achieved in two ways. (i) We have carried out some lifetime--branching-ratio measurements for a principal 5p level and the associated 4s-5p transitions. These measurements have very closely confirmed the accuracy of the results of recent independent emission experiments. (ii) We have critically reanalyzed and revised the literature data for the 4s-4p transitions, as well as utilized the results of a similar critical analysis for the 4s-5p transition array, to establish complete sets of absolute data for these arrays. We have found these data to be mutually consistent from cross-correlation checks between the two arrays, using recent literature data. Finally, we have proposed renormalization factors for other argon transitions based on this analysis.

Critically evaluated transition probabilities, in order of increasing quantum numbers, are compiled for Ba I and II from available literature sources. (Author)

The VUV spectrum of foil-excited fast Zn ions has been studied in search for the intercombination transitions in Mg I-, Al I- and Si I-like ions. The line identifications are supported by decay curve measurements. The wavelength and lifetime data are compared with available theoretical predictions.