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Muonic Coulomb capture ratios and x-ray intensity patterns in four binary mixtures of the gases N2, Ne, Ar, Kr, and Xe have been measured at three atomic ratios. An influence of the concentration has been established. The Lyman series intensity patterns of pure N2, Ne, Ar, Kr, and Xe were measured at pressures between 0.4 and 51 bar and found to depend on the pressure. Possible explanations are discussed.

Measurements of the enhancement of line intensities from oxygen and carbon ions during beam injection of hydrogen atoms into the DITE tokamak have been made for neutral energies of 25 keV and beam powers up to 2 MW. Observations of the spectrum from O encompass the Lyman series in the XUV region (1s−np, n < 9) and Δn = 1 transitions in the VUV and visible regions. The different selection rules for these transitions allow a differentiation between C/X and electron impact excitation of the different (n,l) states. Using theoretical cross-sections and a cascade model for C/X recombination in to hydrogenic ions, the concentrations of impurity nuclei (eg: O8+) are determined from the Δn = 1 VUV lines. This analysis is unsuitable for the Lyman series which lack the C/X signature. Their intensity is determined primarily by the ionisation balance, and the excitation from ground state hydrogenic ion. l state mixing is considered. No indication of statistical repopulation of the sublevels is observed for n < 7.

The frequency distributions of the first six Lyman lines of hydrogenlike carbon, oxygen, neon, magnesium, aluminum, and silicon ions broadened by the local fields of both ions and electrons are calculated for dense plasmas. The electron collisions are treated by an impact theory allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields. These calculations are fully quantum mechanical and include the full Coulomb interaction. Ion effects are calculated in the quasistatic, linear-Stark-effect approximation, using distribution functions of Hooper and Tighe which include correlation and shielding effects. Theoretical uncertainties from the various approximations are estimated, and the scaling of the profiles with density, temperature, and nuclear charge is discussed. A correction for the effects caused by low-frequency field fluctuations is suggested.

The ratio of the intensities of the Lyman alpha (n=2 to 1), Balmer alpha (n=3 to 2) and Balmer beta (n=4 to 2) fine structure components of hydrogen-like ions emitted from plasmas of various atomic number Z is examined. The fine structure intensities of Lyman alpha can only be deduced assuming statistical equilibrium between the fine structure sub-levels of quantum state n=2 for electron densities Ne>or approximately=1013Z9 cm-3, while the fine structure intensities of Balmer alpha and beta can only be deduced assuming statistical equilibrium between the sub-levels of n=3 and 4 respectively for Ne>or approximately=1012Z9 cm-3. At low electron densities (Ne

The authors have developed a model that considers and computes self-consistently the effects of hydrodynamics, atomic physics and radiation emission during the compression of Ar-filled glass microballoons irradiated by high-powered laser pulses. They use it to study a series of experiments done at the University of Rochester Laboratory for Laser Energetics. In some of the cases significant radiation cooling effects induce further compression after the shock wave collapse. Considerations of the timing of the He- and H-like Ar-line emission relative to the hydrodynamic evolution is useful in the interpretation of some spectroscopic density diagnostics performed on these experiments. They suggest that plasma effects such as field-induced ionisation due to the plasma electric microfields may be responsible for some inconsistencies found in the electron densities inferred from Stark-broadening analysis of the Lyman series.

The Coulomb-capture ratios of muons in the metallic solid solutions Au-Ag, Te-Se, Cd-Mg, Nb-V, and Cu-Ni have been measured via the muonic Lyman series intensities. In the case of Nb-V, targets of three stoichiometric ratios were investigated. The results do not agree with the per-atom ratiosA(Z/Z′) assumed to be equal toZ/Z′ (“Fermi-Teller law”) or (Z/Z′)7/6. They are better, but also not in general well, reproduced byA(Z/Z′)=Z1/3 ln(0.57Z)/[(Z′)1/3 ln(0.57 Z′)], deviations occuring in cases of different metallic radii.

A calculation is made of the optical characteristics of a recombination-nonequilibrium plasma of hydrogen-like ions: the gains and attenuation coefficients of light are tabulated for the 5–4, 4–3, 3–2, and 5–3 transitions in the range Z≤30. The problems related to reabsorption of the Lyman series lines are considered. A more accurate estimate is obtained of the maximum electron density in the case of active transitions. The results are presented in the form of graphs convenient for the use in comparisons with the experimental results: the dependences are given of the gain and of the recombination time of an active ion τrec on the electron density and temperature in a plasma originating from various substances and these are supplemented by the dependences of the maximum values of the gain on τrec.

Muonic Lyman series intensities and Coulomb capture ratios have been measured for CuSCN and Cu(SCN)2, and the Cu Lyman series intensities also for Cu metal. No effect due to the ionic charge was found.

Leading members of the Lyman series of He II emitted from a high-density helium plasma have been measured by the use of the Rare-gas Photoelectron Counter which is based on the energy analysis of photoelectrons liberated by XUV radiation. Stationary population inversion between low lying levels of He + is confirmed in a recombining plasma which is interacting with neutral helium. The ratio n 2 / g 2 : n 3 / g 3 : n 4 / g 4 : n 5 / g 5 is found to be 1: 0.6: 1.1: 1.2. A method of determining the electron temperature, the electron density and the ion density from the recombination continua is described. Collisional and recombination processes can explain reasonably the observed level populations.

The ratio of the intensities of the Lyman alpha (n=2 to 1), Balmer alpha (n=3 to 2), Balmer beta (n=4 to 2) and Paschen alpha (n=4 to 3) fine-structure components of hydrogen-like ions emitted from both recombining (ground-state density to 0) and steady-state plasmas of atomic number Z=2, 6 and 12 is examined. Separate account is taken of the (n,l,j) sub-levels up to and including n=5. Ion-induced collisional transitions between sub-levels of the same principal quantum number are considered for the two cases of (i) impurity of atomic number Z emission from a plasma composed mainly of hydrogen and (ii) emission from a plasma composed of full stripped ions of atomic number Z. It is shown that the fine-structure ratios vary from the statistical values and are highly dependent on the electron density and on the ground-state density of the hydrogen-like ion for electron densities below approximately 3*1014 Z8 cm-3 for Lyman alpha, 3*1013 Z8 cm-3 for Balmer alpha and 3*1012 Z8 cm-3 for Balmer beta and Paschen alpha.

The contribution of proton perturbers to the far wings of the Lyman- alpha line of hydrogen is calculated in the adiabatic one-perturber limit. The wing expression is evaluated using the electronic molecular eigenstates of H2+.

The semiclassical impact-parameter method is used to calculate shifts of ionized helium lines in the first three spectral series caused by electrons in a plasma. These shifts together with opposite and smaller shifts due to ion quadrupole interactions are in agreement with observed shifts of lines corresponding to the Paschen series of hydrogen. Adding plasma polarization shifts according to the linearized Debye model to the shifts calculated here results in overestimates by a factor of 2 for the shifts of these lines. For lines corresponding to the Balmer series such addition may be consistent with measurements, while for the Lyman series all present theoretical models are found inadequate.

Spectroscopic experiments have been performed by focusing a 0.263 mu m wavelength laser beam on LiF targets with various transverse dimensions (40

Energies of muonic x rays of the Lyman series of the even sulphur isotopes /sup 32/S, /sup 34/S, and /sup 36/S and of natural phosphorus have been determined with absolute precisions up to 23 parts/10/sup 6/. Equivalent Barrett charge radii R/sub k/,..cap alpha.. have been deduced. Their differences between the sulphur isotopes amount to ..delta..R/sub k/,..cap alpha..( /sup 34/S- /sup 32/ S) = 29.7(1.4) am and ..delta..R/sub k/,..cap alpha..( /sup 36/S- /sup 34/ S) = 18.7(1.5) am. Combining these results with recent elastic electron scattering data, we obtain in a model-independent way ..delta../sup 1/2/( /sup 34/S- /sup 3/ 2S) = 23.1(1.2) am and ..delta../sup 1/2/( /sup 36/S- /sup 3/ 4S) = 13.0(1.2) am.

Muonic X-ray intensities for the Lyman series in oxygen and of the Lyman and Balmer series in chromium have been measured in CrO3 and in crystalline and amorphous Cr2O3. By means of muon cascade calculations which reproduce the measured intensities, angular momentum distributions of the captured muons have been determined for oxygen in a mu atomic level n=14 and for chromium in n=17. The Cr/O capture ratios per atom have been found to be 3.23 in CrO3 and 2.64 in both structures of Cr2O3. This difference is due to the electronic bond structures. The capture probability in chromium is larger in the higher oxidation state which is in contrast to observations in some other elements.

Band-shaped aluminium implants on plane carbon targets were irradiated at 0.1-2*1015 W cm-2 by 600 ps laser pulses of 0.527 mu m wavelength. The resulting blow-off plasmas were diagnosed by X-ray spectroscopy using entrance slits of various dimensions, orientations and positions with respect to the target plane. The authors studied the longitudinal and radial variations of line intensities and Stark widths of He-like and H-like Rydberg series. The effect of time integration was also qualitatively studied by varying implant thickness. Results showed a tenfold decrease of instrumental broadening due to the small lateral expansion of the plasma eliminating radial spatial deconvolution and minimising opacity effects. Comparison with computer modelling showed that n>or=4 Al12+ Lyman series emissions peaked in a 20 mu m width region close to the target and that electron densities deduced from Stark broadening agree well with the simulations.

A simple formula is derived for the escape probability of photons in optically thick resonance lines of hydrogenic ions. The result is valid whenever quasi-static Stark broadening predominates in the line wings, a condition that is satisfied in most laser-produced plasmas. In contrast to impact (Lorentzian) broadening, Stark broadening tends to decrease the probability of photon escape as the plasma density increases.

The per-atom Coulomb capture ratio $A(\mathrm{N}\mathrm{b},\mathrm{V})$ of negative muons in the solid solution Nb-V has been measured for five stoichiometric ratios $S(\mathrm{Nb}/\mathrm{V})$ ranging from 0.046 to 18.5. No change of $A(\mathrm{N}\mathrm{b},\mathrm{V})$ with $S$ was observed. The weighted mean is 1.21\ifmmode\pm\else\textpm\fi{}0.04. There is also no experimental evidence for a variation of the muonic-Lyman-series intensity patterns of both elements with $S$.

Optical measurements of single electron capture in He2+ -Li collisions are reported in the energy range 0.55–10keV/amu. These low energies were inaccessible in our earlier work on the same system [1]. Cross sections for emission of the 1s−np (n = 2, 3, 4) Lyman series of He II have been measured with a VUV grazing incidence spectrometer. From these we have deduced the total capture cross section σt, and the subshell-selective capture cross sections σ3p and σ4p. Correction factors connected with the polarisation of the emitted radiation were applied to our data, using theoretical results of Fritsch and Lin [2], who calculated capture cross sections for nlm−states. Our results for σt, are in excellent agreement with very recent charge state selection measurements by Varghese et al. [3]. Both the total and the partial cross sections agree very well with theoretical results by Fritsch and Lin [2]. Comparison with other experimental and theoretical results is also made.

The high resolution electron impact excitation of the H2 and D2 Lyman bands has been investigated. Particular attention has been paid to two series of (H2−2Σu+) resonances which decay into the B1Σu+(ν′) states.

Photodissociation of water vapor to produce H(n=2) atoms was examined from threshold to 500 A. The experimental threshold of 813.0 A nearly coincides with the thermodynamic limit. Excitation cross sections rise slowly from threshold to a maximum value of (1.55±0.12) ×10−18 cm2 at ∼709 A and decreases to a negligible value below 550 A. Structure in the excitation function is attributed to predissociation of Rydberg series converging to the ? 2B2 state of H2O+.

The polarisation of selected Lyman and Werner bands and also of Lyman- alpha radiation are measured as a function of impact electron energy in the range from threshold to 300 eV. Polarisations in excess of 0.2 are obtained in certain instances. The results for Lyman- alpha confirm and extend those of Ott et al. (1970). Extrapolations of the results to the thresholds are compared with estimates based on angular-momentum conservation and symmetry arguments. For the Werner emission a further comparison is made with a 'pseudo'-threshold polarisation measurement using the scattered-electron-delayed-photon coincidence technique. The apparent excitation functions for the two molecular emissions are derived from the measurements of polarisation. In both cases good agreement is obtained with the semi-empirical data of Gerhart (1975). Comparison is made with the results of other workers wherever possible.

Except in the simplest of physical situations, broadband spectrum formation in dense optically thick plasmas is the result of a highly complex set of nonlinear phenomena. At NRL, we are developing models to investigate a number of the theoretical issues related to the interpretation of time integrated X-ray spectra. Many of the individual features of these spectra can be understood qualitatively and modeled quantitatively (see Ref. 3). However, a number of questions concerning the self-consistency of theoretical treatments of an entire spectrum remain. A few of these questions will be examined and discussed in this talk within the context of imploding plasmas. Spectrum formation at high ion densities will be described using an argon K-shell model containing atomic structure up to n = 10 in both hydrogen and helium-like ionization stages as well as lower excited states in the lithium-like system. Lyman series emission is computed along with three prominent satellite lines of the H- and He-Lα lines and He 1s2−1s2p3P intercombination line. Local Stark profiles are also computed and used for Lα, Lβ, and Lγ lines of both the hydrogen and helium-like series. For the higher lying lines, which are strongly overlapped at high densities, collisional width estimates for Voigt profiles are used. The overlap of satellite, intercombination, and Lα resonance lines, on the other hand, occurs as the result of overlapping Stark and Voigt profiles. The influence of these different line profile assumptions on spectrum formation at high density will be discussed in terms of the problems of self-consistently inferring plasma conditions during emission, such as temperature, density, and plasma ionization state. These are usually inhomogeneous in both space and time. However, some recent progress at NRL enables us to theoretically address these problems. We will discuss them within the context of post-processing the temperature and density profiles that are predicted by hydrodynamics calculations of imploded, Argon/DT filled, glass microballoons.

The Lyman spectrum of hydrogen has been computed for a number of flare models, characterized by the column density of hydrogen atoms in the ground state (N1), the electron density (ne) and the electron temperature (Te). Broadening by the thermal Doppler effect and by Stark effect has been accounted for. The source functions for the individual lines of the series have been derived from non-LTE calculations of the excitation in hydrogen flares. The aim of the investigation is to evaluate the use of the intensities in between two successive Lyman lines for a determination of the value for N1, which is a physical parameter of the flare for which only indirect determinations are available. Whilst in principle this method could give reliable results, its practical application meets with difficulties which hardly can be overcome. Therefore, one probably has to base the N1 determination on the highest line resolvable in the spectrum.

The cross sections for the excitation of Ly-beta and H-alpha when methane is dissociated by electron impact have values of 17.1 by 10 to the -19th power sq cm and 26.0 by 10 to the -19th power sq cm, respectively, at an electron impact energy of 100 eV. These results are in disagreement with the implications of recent polarization measurements of H-alpha radiation that suggest negligible H(3p) excitation in the dissociation of CH4 by electron impact.

It has been noted that line radiation-for example, the first member of the Lyman series of C5+-is optically thick at the surface of a laser-irradiated carbon target. Optical depths of the order of 104 can be anticipated with appropriate focusing geometry. Using such an optically thick and broadened line source it is calculated that population inversion and a measurable super-radiant gain can be achieved by resonance pumping in neighbouring ion species.

Energies of muonic X-rays of the Lyman series of seven light natural elements (F, Na, Al, Si, P, S and K) have been determined with an accuracy of between 15 and 30 eV. Equivalent charge radii have been deduced. For μ−-K, transitions to the 2s state allowed an additional constraint on the Fermi c-t diagram. The results are in good agreement with, and generally of an order of magnitude higher precision than, comparable electron scattering data.

Muonic x-ray spectra have been measured for ${\mathrm{N}}_{2}$, S${\mathrm{F}}_{6}$, and Ar at pressures up to 20 atm at room temperature and in the liquid or solid state, and for ${\mathrm{O}}_{2}$ at 20 atm and CO, NO, and a ${\mathrm{N}}_{2}$+${\mathrm{O}}_{2}$ mixture at 10 atm. Relative intensities of the higher members of the muonic Lyman series of N decrease monotonically with decreasing pressure (density). A similar effect is observed for F in S${\mathrm{F}}_{6}$, where some effect was also noted for the S x rays. A gas-pressure dependence in Ar was not observed in the pressure range covered. The density effect can be modeled approximately by a muonic-atom cascade code in which the $K$-electron refilling width is related to the gas density, which determines the frequency of collision of the atom with neighboring atoms or molecules. The difference in behavior between ${\mathrm{N}}_{2}$ or S${\mathrm{F}}_{6}$ and Ar at comparable pressures provides evidence for the "Coulomb explosion" that is expected to occur when a negative muon is captured by a polyatomic molecule.

Results are presented of experimental oscillator-strength measurements for four Lyman, one Werner, two B′-X and two D-X bands of molecular hydrogen in the wavelength region between 850 and 900 A. A photoabsorption technique and equivalent-width analysis similar to that described in the first paper of this series was employed but, in this case, all measurements were taken with the absorbing gas at liquid-air temperature. This procedure resulted in a simplification of the absorption spectrum, making it possible to study lines which were unresolved at room temperature. Excellent agreement with the most recent theory is observed for the Lyman bands, but the experimental Werner band oscillator strength is slightly low, consistent with the trend observed above 900 A in the previous work. No other experimental results exist for the bands studied, and no theoretical oscillator strengths are available for the B′-X and D-X bands.

Blue shifts of \ensuremath{\sim}85-60 m\AA{} have been observed for the first five members of the C vi Lyman series emitted from a laser-produced plasma plume at an electron density near ${10}^{21}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. These shifts are much larger than density-dependent effects associated with electron collisions and inhomogeneities in ion-produced electric microfields and opposite to plasma polarization shifts according to the linearized Debye model. A nonlinear Debye-type model is consistent with the measurements.

Muonic x-ray yields have been measured for Al, ${\mathrm{AlF}}_{3}$, ${\mathrm{AlCl}}_{3}$, ${\mathrm{AlI}}_{3}$, KCl, KBr, KI, Cd, ${\mathrm{CdF}}_{2}$, ${\mathrm{CdCl}}_{2}$, ${\mathrm{CdBr}}_{2}$, ${\mathrm{CdI}}_{2}$, Sn, ${\mathrm{SnCl}}_{2}$, ${\mathrm{SnCl}}_{4}$, Sb, ${\mathrm{SbF}}_{3}$, ${\mathrm{SbCl}}_{3}$, and ${\mathrm{SbCl}}_{5}$. The yields were normalized with the total intensity of the Lyman series. The capture ratios between Coulomb capture in the anion and the cation were determined for all compounds listed. These ratios are not well reproduced by the Fermi-Teller "$Z$ law." Chemical effects in the intensities were observed. All observed intensities were compared with cascade calculations assuming a modified statistical population of the levels with $n=20$. In a number of cases this procedure does not yield a satisfactory reproduction of the experimental data.

The asymmetry of the first two spectral lines of the Lyman series of hydrogen is calculated. Detailed profiles, which include the effects of time ordering and asymmetry, are presented for a region of the line profile from the center to the line wings, where the impact approximation for the electrons and the quasi static approximation for ions are reasonably applicable. Deviations in the line wings from “Unified theories” are of the order 0–15% for the profile parameter range considered. Such deviations should have only a minor effect on the computed asymmetry. The far red wing of both Ly-α and Ly-β is seen to dominate the blue wing. In the near wings the blue intensity becomes equal to the red intensity. From here into the line center, the blue intensity is larger than the red intensity. In the case of Ly-β, there is the expected enhancement of the blue peak and reduction of the red peak. The calculated profiles are compared with previous calculations and recent experimental results.

Measurement of shifts in the neon Lyman- alpha , - beta and - gamma lines and the He-like 1s2-1s2p line have been obtained in laser-compressed plasmas at ne approximately 3*1022 cm-3 and Te approximately 300 eV. Calibration of the neon line wavelengths was determined relative to the emission lines of higher Z elements present in the microballoon glass shell. A trend towards larger red shifts in the wavelengths of the lower neon Lyman series members was observed, and the neon He- alpha line was observed to be blue shifted. These trends are shown not to be the result of refractive index corrections to the dispersion of the crystal spectrometer used, and are unlikely to be the result of differential spatial or Doppler effects between the neon and the calibration lines. Assuming that the measured red shift of about 10 mAA for neon Lyman- alpha is an indication of the magnitude of the absolute shift, then the observed shift is an order of magnitude greater than predicted by current plasma polarisation shift theories at the plasma densities and temperatures obtained in the present experiment.

Zero-field quantum beats were observed in Lyman-α emission (1216 A) from hydrogen atoms formed by beam-foil interaction of 50 to 270 keV proton beams. Relative excitation crossections for magnetic substates of the 2P level of hydrogen were derived from modulation amplitudes and are discussed with respect to the excitation process.

367 THE LISBON AND LYMAN SERIES 368 GENERAL DISTRIBUTION OF THE LYMAN SERIES 369 FIELD RELATIONS AND MEGASCOPIC DESCRIPTIONS OF THE LYMAN SERIES The Young's Pond Locality 369 The Mormon Hill Locality 371 The Parker Hill Locality 372 MICROSCOPIC DESCRIPTIONS Porphyry Schist of the Young's Pond Locality 372 Pebbles of the Conglomerate Schist of the Young's Pond Locality . 374 Parker Hill White Schist 375 Parker Hill Dark Schist 376 GENERAL CONCLUSIONS ON THE ORIGIN OF THE LYMAN SCHISTS Porphyry Schist of the Young's Pond Locality 377 Parker Hill White Schist 378 Conglomerate Schist of the Young's Pond Locality 379 STRUCTURAL RELATIONS OF THE LYMAN SERIES 380 ACIDIC EFFUSIVE ROCKS EAST OF THE APPALACHIAN PROTAXIS 380

A study of the generation and transfer of radiation in gases at temperatures greater than 10 000°K usually involves spectroscopy in the vacuum ultraviolet spectral region, whether for the determination of such quantities as oscillator strengths, line shapes, and absorption coefficients fundamental to an understanding of the detailed emission and absorption processes transpiring in the medium, or for the laboratory simulation and identification of spectral lines such as observed by astrophysicists. Results of such endeavors are equally important to an understanding of the plasma physics and of mechanisms of energy loss which often determine the maximum heating rate of, for example, controlled fusion devices, as well as to astrophysicists in the formulation of model atmospheres and the determination of stellar structure. For these purposes, laboratory sources are needed which operate at high enough density to produce useful spectra and yet are capable of simulating temperatures and equilibrium conditions of interest to astrophysicists. To this end a T -type electromagnetic shock tube operating at ∼20 000°K has been developed to generate a uniform high density atmosphere into which tracer gases are added in controlled amounts, producing variable degrees of opacity in the vicinity of broadened spectral lines of known shape, such as the Lyman series of hydrogen. Also, two θ -pinch devices operating at temperatures in the million-degree range, suitable for simulating corona equilibrium conditions and solar spectra as well as producing resonance lines of variable optical depth, are described. Experimental complexities peculiar to various regions of the extreme ultraviolet from 10 A to 2000 A are outlined, as is a discussion of absolute intensity determinations.

Observations of the geocoronal hydrogen absorption feature at the center of the solar Lyman α emission line, together with previously published absorption measurements, are analyzed and compared with the predictions of the Kockarts and Nicolet model and the Liwshitz model of the terrestrial hydrogen distribution. The results show that the hydrogen density at 100 km is between 1.25 and 2×107 cm−3 (for the Kockarts and Nicolet model) for a wide range of exospheric temperatures, that the geocoronal hydrogen abundance decreases with increasing exospheric temperature, that there is reasonable agreement with near-simultaneous satellite Lyman α airglow observations, and that the absorption data are not accurate enough to distinguish between the models. Measurements of atomic hydrogen with mass spectrometers give densities that are larger by 2 orders of magnitude and therefore must be rejected in favor of the optical results.

The authors investigate shift and asymmetry of broadened hydrogen lines in plasmas. All contributing multipoles and interactions between states with different principal quantum numbers (quenching effect) have been included in the atom-perturber potential V(t). Numerical results are given for Lyalpha line in the impact limit. Especially, for T=5104K, the shift arising from quenching effect is eight times greater than that arising from quadrupole and monopole.

A more general description of the Cotton—Mouton effects in atoms and molecules is presented. By use of a time‐dependent double perturbation approach, closed and spectral expansion expressions of required molecular parameters are derived. The method is applied to the hydrogen atom to generate accurate Cotton—Mouton dispersion curves for a wide range of wavelengths, including the first two lines of the Lyman series.

The success of the hollow cathode discharge in helium in exciting the spectra of various metals suggested that a similar method might be applied to excite the spectrum of arsenic. It was in the course of this work that plates were obtained which revealed with remarkable intensity the Lyman series of hydro­gen, extending down to the 15th member. The most interesting feature of the series, however, is the anomalous distribution of intensity among its members. Instead of the intensity gradually falling off as we go to higher members, a sudden enhancement is observed in the intensity of the 10th and 11th members and then an abrupt fall so that the remaining members are only just observable. The appearance of the series is such as immediately to suggest the occurrence of a kind of resonance effect. The experiments were therefore repeated under various conditions in order to investigate the cause of this observed anomalous intensity and to discover, if possible, the type of impact involved in the production of such a phenomenon. In two preliminary notes, the main conclusions which have been obtained have been reported and it is the purpose of this paper to describe these investigations and the conclusions reached. Experimental . The experimental use of the hollow cathode source is well known and has been described previously by various writers but on account of the importance of the phenomenon that has been observed, it is considered worth while to present details of the method employed. Some metals, like aluminium, are generally used directly as the cathode, but Paschen has found that the source can be adapted also for metals of low melting points or those which vapor rapidly, in which case the metal in question may be placed in a carbon (or tungsten) hollow cathode. The cathode in these experiments, was a thin hollow cylinder of carbon, C, fig. 1, of length 3·5 cm. and diameter about 1·5 cm. The cylinder was closed at one end N, which terminated in a kind of box of length 0·5 cm., the inner wall W of which was perforated. This box served as a reservoir to contain metallic arsenic, whose vapour entered the cathode through the perforated wall. A similar cathode was used by Takahashi* in his experiments on Zn and Cd.

Classical-path calculations for the Stark broadening of the Lyman-β line of hydrogen are presented using a procedure outlined in a previous paper. All multipoles in the perturber (free electron)—atom interaction are included and time ordering of the operators in the S-matrices is retained. Comparison is made with previous calculations. In particular, the profiles given here have very nearly the same half widths as the profiles of Kepple and Greim but show a significant increase in the intensity at the line center.

The LCAO–MO–CI method is applied to the study of the electronic transition moment of the Lyman bands of H2 (B 1Σu+–X 1Σg+) over the range of internuclear separations 1 ≤ R ≤ 6 a.u. It is found that configuration interaction is responsible for a strong nonlinear variation of the transition moment with internuclear distance (maximum transition moment at 3.0 a.u.). Comparison with other calculations indicates that the method is applicable to more complicated molecules and permits the examination of how individual electron correlation effects contribute to the transition moment.

The spherical Lyman-β radiative transfer problem is solved for several theoretical models of the hydrogen geocorona. Comparisons of the computed intensities with the experimental observations of Lyman β and Balmer α airglows show that the geocoronal Balmer α contribution is superimposed on a uniform background of about 4 R. The 4 R background is probably galactic (or extra-galactic) in origin. The column density of hydrogen required to account for the telluric Balmer α component is about 5 × 1013 atoms per cm² above 650 km for a 950°K exosphere.

A recent paper by A. W. Gauger opens the possibility of an interesting and novel method for gaining information on the mechanism of hydrogenation catalysis by nickel and other metals. Gauger bombarded with electrons a target of catalytic nickel in the presence of a low pressure of hydrogen, and observed the critical electron velocities at which the occurrence of characteristic radiation could be detected by the photo-electric current which it produced by falling on a collecting plate connected to an electrometer. Gauger reported a number of critical potentials, several of which he associated with the first members of the Lyman series and the ionisation of atomic hydrogen respectively. The results were interpreted as indicating the presence of atomic hydrogen in the system comprising hydrogen and a nickel catalyst.

Isotope effects in Lyman and Werner systems of molecular hydrogen, HD and molecular deuterium, calculating band strengths, oscillator strengths and Franck-Condon factors

The X-ray spectrum emitted from the deuterium plasma in the Scylla fast magnetic compression experiment has been studied with a beryl, single-crystal, X-ray diffraction spectrometer. Prominent lines are identified from the HeI-like spectra of Na X, Mg XI, A1 XII and Si XIII wall impurity ions as well as the H-like Lyman series of O VIII. The shape and absolute magnitude of the continuum spectrum indicate that the plasma electron temperature is 345±40 eV and that the soft x-radiation arises primarily from electron recombination with small amounts of highly stripped impurity ions. Broadening measurements of the spectral lines in the X-ray region show that the Doppler temperature of impurity ions is considerably greater than the corresponding deuterium ion temperature.

If the distance between two or more energy levels is comparable to their natural breadth, the levels cease to act independently. The coupling between the levels is then describable by means of a "damping constant matrix." The usual discussions concern themselves with a diagonal damping constant. Below a systematic treatment of emission, absorption and fluorescence is given without this restriction and it is shown how in general the frequencies of emission lines are affected by this radiation coupling. The theory is applied to the calculation of the polarization of fluorescence radiation. It is shown that the coupling state of the lower group of levels of the fluorescence line does not influence the polarization. Results of detailed calculations are given for the polarization of $\mathrm{H}\ensuremath{\alpha}$ excited by absorption of the second line of the Lyman series.