Triplet Series Research Articles

Orbital relaxation in the Rydberg series of the He atom

AbstractThe orbital behavior of both the singlet and triplet Rydberg series for 1sns configurations of the He atom has been investigated using one‐ and two‐configuration Hartree–Fock wave functions. The core orbital within the triplet series changes negligibly; however, a contract trend is noticeable as the Rydberg orbital penetrates more into the core region, which is in contrast to that found in the 1s2ns 2S Rydberg series of Li atom. Although some properties of the whole atom can be calculated, the core relaxation of the singlet series can not be drawn without ambiguity because a two‐configuration correlated wave function has to be used, and thus the orbital picture is lost.

High-resolution studies of the Stark effect in even-purity Rydberg states of Ca I

High-resolution laser-atomic-beam spectroscopy has been applied to the study of the quadratic Stark effect in calcium 4sns3S states with principal quantum number n ranging from 14 to 45 and 4snd3D states with n=10 to 30. For the3D states the electric-field-induced splittings are comparable with the fine-structure splittings. The analysis takes account of both field-induced fine-structure mixing and zero-field deviations from LS coupling. The resulting polarisabilities are compared with calculations based on the Coulomb approximation. Satisfactory agreement is obtained. Accurate values of the fine-structure intervals in the 4snd3D series (n=14 to 30) and of the44Ca-40Ca isotope shift in a number of transitions from the 4s4p3P2state to 4sns3S1and 4snd3D3states have also been determined. From the latter data the residual level isotope shift in the 4s4p3P2state is derived. Fine-structure and Stark effect data for the 4snd levels near n=15, where the singlet and triplet series cross, indicate a stronger singlet-triplet mixing than previously assumed. This is explained in terms of small admixtures of doubly excited configurations in the 4snd levels resulting in a strong off-diagonal spin-orbit interaction.

Absorption spectrum of the laser-populated3D metastable levels in barium

The paper deals with the details of the absorption spectrum of the 3D metastable term in barium. The 3D term was selectively populated with a tuneable dye laser. The fundamental triplet series (6s5d3D-6snf3F) is identified and extended out to n=32. In addition, the absolute photoionization cross section was measured at 303 nm and found to be (18+or-4)*10-18cm2. The relative cross section from 303 to 250 nm was also measured with the absolute scale set by the measurement at 303 nm and was found to be nearly constant in the wavelength region measured.

Production of alkaline earth metastable states by a discharge in a heat pipe

An experiment is described in which the first excited metastable states nsnp3Po and nsnd3D of the alkaline earths Mg, Ca, Sr and Ba are populated by a continuous discharge running through a metal vapor maintained by a heat pipe. The number of atoms obtained in these excited triplet states is large enough to allow the observation of the series members in a conventional atomic absorption experiment. The Argonne 30 foot Paschen-Runge spectrograph has been used to record the spectra with a 0.37 AA mm-1 reciprocal dispersion. The wavelength uncertainty of +or-0.002 AA gives improved wavelength values for many lines measured previously in emission and gives an energy scheme for the highest terms of the series nsn's3S1,nsn'd3D and nsn'f3F0 that is more accurate than previously reported. The variations of the quantum defect have been fitted and the ionization limits, extrapolated from the triplet series, are compared with those obtained from the long principal series ns2 1S0-nsn'p 1P10.

The effects of cascading and metastable atoms on the determination of electron temperature from relative line intensities in a tenuous helium plasma

The effects of cascading and electron-metastable atom interactions on he determination of electron temperature from the relative intensities of helium singlet and triplet series spectral lines are considered. It is found that the presence of metastable atoms will have a small effect if cascading effects are measured experimentally. Limitations on the applicability of the technique and criteria for determining its validity are presented.

Structure of Resonances in Electron Scattering by Hydrogen Atoms

A study of the structure of resonances just below the $n=2$ excitation threshold in electron scattering by hydrogen atoms is carried out by utilizing an approximate method adopted from the projection-operator formalism. Analytic expressions for the level width near the threshold are obtained for both the singlet-and triplet-compound-state series with zero total angular momentum. It is found that the level widths behave like the level spacings in that they decrease exponentially as the levels approach the threshold. Nevertheless, the ratio between the level spacings and widths remains a constant less than 1. It is then concluded from the study that within the approximations adopted in the method, neither the singlet nor triplet series of the compound states become overlapping near the threshold. However, the Lamb shift may, by removing the degeneracy in the $n=2$ levels, cut off these infinite sequences of compound states, thereby restricting the number of allowed resonances. The interference between potential and resonance scatterings is also examined.

Die Druckverbreiterung der diffusen Heliumlinien, Vergleich zwischen Messung und Theorie im quasistatischen Bereich

It is difficult to discriminate between theories of pressure broadening of spectral lines through comparison with experiments. Line profiles are insensitive with respect to details of the theory, and it is difficult to keep experimental conditions clear and certain enough to make the comparison relevant. We used measurements of VIDAL 1 which are satisfactory from the experimental point of view. The wings of the diffuse He-lines 2P — nD are compared with those calculated by quasistatic theory. Part B deals with STARK effect splitting of the upper level. Part C describes the quasistatic theory of the line wings, and discusses the probability function of the so called micro field strength. In part D the results of the calculation are compared with the measurements. The comparison is relevant only for the violet wings of the triplet series. The red wing of the triplet lines and the violet wing of the singlet lines are disturbed by the forbidden component 2P — nP. The red wing of singlet lines is experimentally too inexact because of disturbing wings of neighboring triplet lines. The slope of the violet side of the triplet wings shows good agreement between theory and measurement for the far wing (large Δv). For decreasing Δv the experimental curve stays below the theoretical curve. For comparison of wing intensities it proves to be important to normalize the line profiles. It is seen that the measured height of the wings increases less with increasing main quantum number than the theoretical height.

Oscillator Strengths for Singlet and Triplet Series in Neutral Helium

Oscillator Strengths for Singlet and Triplet Series in Neutral Helium

Excitation of Molecular Nitrogen by Electron Impact

Relative cross sections for excitation of the triplet series of molecular nitrogen have been obtained. The cross sections have a maximum within a few volts of threshold as expected for electron exchange collisions. In particular, the C 3IIu state has a sharp maximum within a few tenths of a volt of threshold and then decays sharply. The A 3Σu+ state has an increasing slope through the Franck—Condon region and then is a strictly linear function of energy for about 1½ V. It subsequently reaches a maximum and starts to decay. This leads to the postulate that the region of increasing slope is caused by the continual excitation of new vibrational levels and that the excitation function of a given vibrational level may be linear to near threshold. This interpretation is shown to be consistent with the experimental data.

Absolute Electron Excitation Cross Sections of Helium

The absolute apparent electron excitation functions of helium were measured for the 3/sup 1/S, 4/sup 1/S, 5/sup 1/S, 6/sup 1/S, 3/sup 1/P, 4/sup 1/ P, 3/sup 1/D, 4/sup 1/D, 5/sup 1/D, 6/sup 1/D, 3/sup 3/S, 4/sup 3/S, 5/sup 3/S, 3 /sup 3/P, 3/sup 3/D, 4/sup 3/D, 5/sup 3/D, and 6/sup 3/D states at pressures sufficiently low so that the effects of radiation imprisonnaent and collisional excitation transfer can be neglected. The data were corrected for polarization of the radiation and cascading from the upper excited states, and the true excitation functions obtained. The peak values and shape of these excitation functions are compared with results of other laboratories. Generally good agreement is found with previous works where the collisional excitation transfer was properly reduced and allowance made for the cascading effect. The experimental cross sections show satisfactory agreement with the theoretical values calculated by the Born approximation for the /sup 1/S and /sup 1/P states at high electron energies, but are about four times larger than the theoretical values for /sup 1/D states. For the triplet series, the experimental cross sections exceed the calculated values by factors of ten to one hundred or more. It is concluded that the populationmore » of the triplet states is produced mainly by processes other than direct excitation. (auth)« less

The helium chromosphere.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The helium chromosphere. Athay, R. G. Abstract The flash-spectrograms obtained by the High Altitude Observatory expedition to the 1952 eclipse in Khartoum contain several helium lines that are suitable for photometric reduction. Some of these lines have not been studied quantitatively at previous eclipses, and our spectrograms were taken with much greater height resolution than had been previously attempted. These features make a study of the helium data from the 1952 eclipse of special interest. The Hei data include the first four lines of the 23P - n3D series, the first three lines of the 2~P - n3S series, the first line of the 2'P - n'D series and the first three and fifth lines of the 2'? - n'S series. The Heii data are for X4686, 32D - 42F0. The data show maxima in the surface brightness of the chromosphere at the limb at heights of I 100 km for HeI emission and 1500 km for Heii emission. Both the hydrogen and helium data show that if the chromosphere is assumed to be uniform the radial optical depth at X5oo is 200 at the height where the maximum Hei emission occurs. These large optical depths exclude the possibility of excitation of chromospheric helium by ultraviolet coronal radiation if the chromosphere is uniform. Kinetic temperatures obtained from an analysis of the continuum data under the assumption of a uniform chromosphere are too low to produce the observed excitation of helium. Thus the assumption of a uniform chromosphere appears to be invalid for the helium data, and we assume a two-region model with all of the helium emission coming from one region. The triplet series of Hei have excitation temperatures of 50000, and the singlet series have excitation temperatures of 15,0000. If we assume approximate thermodynamic equilibrium for HeiT and the singlet series of Hei and use a relative abundance of hydrogen to helium of 7: 1, the observed line intensities for both Hei and Heii require kinetic temperatures of 19,000 in the regions above 1500 km that emit the helium radiation. If we vary b1 within the limits < b1 < i~~ the kinetic temperature in the helium region varies between 14,5000 < Te < 26,0000. The maximum in the Heii emission at 1500 km leads to Te 20,0000, in agreement with the values obtained by other methods. Continuum data show that the electron temperatures and densities below 4000 km in the regions that do not emit helium radiation are essentially unchanged from the results obtained on the assumption of a uniform chromosphere (Athay et al. 1955). Above 4000 km the nonuniform model leads to higher temperatures in these regions. The eclipse spectrograms show conclusively that above 5000 km the helium radiation is in the spicules. This work was supported by the Office of Naval Research and carried out in cooperation with the Naval Research Laboratory. Athay, R. G., Meozel, D. H. Pecker, J-C., and Thomas, R. N. 1955, Ap. J. Supplement 12, 505. H~gh Altitude Observatory, Boulder, Colo. Publication: The Astronomical Journal Pub Date: June 1955 DOI: 10.1086/107180 Bibcode: 1955AJ.....60..150A full text sources ADS |

Fine structure in the mercury singlet terms

The fine structure occurring in a number of line spectra has been reasonably accounted for by the theory of nuclear spin, but up to the present the complexity of the fine structure in mercury lines has remained unexplained, more lines occurring than theory demands. Because of the weakness of the singlets in the sources usually employed most of the investigations on mercury fine structure have been carried out on triplet and intercombination lines. The fine structures in the singlest series should yield more readily to analysis than in the triplet series, being simpler, and for this reason are investigated here. A comprehensive survey of the experimental work done up to 1926 in mercury was given by Ruark who succeeded in accounting for the majority of the components in several triplet lines by giving a number of levels as threefold multiplicity. Only one singlet level 6 1 P 1 was discussed and the multiplicity attributed to this was seven. In a previous communication an account was given of a method for increasing the relative and intrinsic intensity of the singlet series and of inter-combination lines involving upper singlet levels. The series 6 1 P 1 — m 1 S 0 , 7 1 S 0 — m 1 P 1 and 7 3 S 1 — m 1 P 1 are particularly strengthened and these have been examined for fine structure with a Fabry-Perot interferometer. It was stated in a preliminary note that λ 4916 (6 1 P 1 — 8 1 S 0 ) had four components and that the members of the series 7 1 S 0 — m 1 P 1 , 7 3 S 1 — m 1 P 1 were sextet. These observations are now somewhat extended, fainter components having been found. Whilst this paper was in the course of preparation, a communication was received from Venkatesachar and Sibaiya giving the structures of some of these lines. Venkatesachar also stated, that in a short note to 'Nature,' which was overlooked by the writer, Hansen found that λ 4916 was a quintet. These results will be discussed later.

The Spectrum of Gallium II And The (4s4p2) Configuration in Gallium I and Indium I

The spectrum of gallium has been excited in a hollow cathode discharge in helium and photographed in the region from $\ensuremath{\lambda}10,000\ensuremath{-}\ensuremath{\lambda}200$. about 90 lines so excited have been classified in singlet and triplet series of Ga II. Peculiarities in the run of intensities in successive members of series have been found due to the excitation by helium which is sufficient to excite only terms greater than 12,000 $\ensuremath{\nu}$-units in this spectrum. Absolute term values are calculated and the lowest term is $(4{s}^{2})^{1}S=165458$ corresponding to an ionization potential for Ga II of 20.43 volts. Tables of classified lines and of term values are given. The lines arising from combinations of $(4{p}^{2})^{4}P$ and $(4{p}^{2})^{2}S$ with $(4s4p)^{2}P$ of Ga I have been identified and values of these terms are given. Preliminary work on the excitation of the indium spectrum in helium has enabled the location of $(4{p}^{2})^{4}P$ in In I and its term values and combinations with $(4s4p)^{2}P$ are given.

The exclusion priniciple and aperiodic systems

Section I .—The exclusion principle of Pauli was introduced into the old quantum theory as an empirical fact that had been brought to light in the ordering of spectra. The new mechanics has provided some sort of explanation of the principle, for in a closed system with many electrons the mathematically possible stationary states can be separated into a number of groups, with the property that transitions between stationary states in different groups cannot occur. One of these group is made up of the stationary states corresponding occur. One of the these groups is made up of the stationary states corresponding to wave functions that are antisymmetrical in the co-ordinates of the electrons. Apart from accidental degeneracies, the stationary states in different groups have different energy values. The exclusion principle then states that only energy values belonging to the antisymmertical group are found in nature. The exclusion principle has had great success not only in explaining the spectra of helium and of more complicated atoms, but also, under the form of the Fermi-Dirac statistics, in accounting for metallic conduction and ferromagnetism. In all these phenomena we are dealing with systems is stationary states, possessing energy values which are discrete, although they may lie very close together. Now, as was first emphasised by Oppenheimer, we must also use antisymmetrical wave-functions to describe aperiodic phenomena, such as the collision between an electron and an atom. If we do not, we obtain probabilities for the formation of atoms whose wave-funtions are not antisymmetrical, as we shall show in section 4, where we consider the collision between an electron and a helium atom. A helium atom described by a symmetrical wave-function would show a singlet series in palce of the observed triplets and triplet series in place of the observed singlets. The wave-functions of open systems are essentially degenerate; the symmetical and antisymmetrical solution are not separated from one another by a finite energy difference; but for any arbitrary value of the energy (and of the other integrals of the motion) we can form a symmetrical and an antisymmetrical solution. This is somewhat fundamental difference between open and closed systems. For closed systems containing two electrons there exist only the symmetrical and the antisymmetical solution; but for open systems we might take any combination of the two. In fact, to describe an observable phenomenon such as a collision, the wave-function that it would first occur to us to use is a combination of the two. To fix our ideas we shall discuss the collision between two electrons. Our arguments could equally well be applied to the collision between an electron and a hydrogen atom, the problem originally discussed by Born; but the former is the simpler case, and perhaps illustrates our theory better.

Vari'ation in the Intensities of Mercury Spectrum Lines with Pressure of the Vapor

The relative intensities of spectrum lines of Hg vapor in the d.c. arc and at a pressure of ${10}^{\ensuremath{-}3}$ mm in a high frequency electrodeless discharge have been measured for wave-lengths ranging from 7000 to 3000A. There is a decided increase in intensity, relative to the triplet line 5460, of the singlet members in the low pressure discharge, the sharp series showing the greatest increases. The relative intensity increases rapidly with ascending members of the series. Five new lines in the sharp singlet series were observed. Combination singlets appeared strong in the red in the low pressure discharge. The first members of the triplet series do not show much change but the higher members show an increasing intensity at low pressure. Combination lines also show decided increase in the low pressure discharge.

Absorption and Emission Spectra of the Geissler Discharge in Mercury Vapor and in Mixtures of Mercury and Hydrogen

In a quartz tube 4 cm in diameter, mercury vapor was maintained at about 3 cm pressure and a current of.5 amp. was sent from a tungsten filament cathode to a nickel anode 18 cm away. The absorption of light from a quartz Hg arc lamp on passing transversely through the discharge tube was determined with a small Hilger quartz spectrograph. (1) Absorption by the continuous positive column. Several lines of the diffuse and subordinate triplet series were absorbed by atoms in the $2p$ states, $2p\ensuremath{-}2s$ lines very strongly, $2p\ensuremath{-}3s$ lines less strongly, $2p\ensuremath{-}3d$ lines strongly, $2p\ensuremath{-}5d$ lines less strongly, $2p\ensuremath{-}5d$ lines weakly. No trace of absorption of combination lines by $2p$ atoms or of absorption by other excited atoms was observed. An unidentified faint line 4279 showed absorption. These results confirm and extend those reported by Metcalfe and Venkatesachar. The absorption by atoms in the $2{p}_{1}$ state is greatest but of the same order of magnitude as that by atoms in the $2{p}_{2}$ and $2{p}_{3}$ states. This is hard to reconcile with the extremely short life of the $2{p}_{2}$ state. (2) Absorption by the striated positive column, obtained by adding hydrogen. The bright region of the striation showed greater absorption of the $2p\ensuremath{-}2s$ lines than did the dark regions. (3) Emission spectra of various parts of the discharge. The negative glow emitted the arc spectrum and the spark line 2848. All these lines appeared with diminishing intensity through the Faraday dark space. The continuous positive column emitted the arc spectrum. The striated positive column emitted the arc spectrum and HgH bands. The intensity of emission attained its maximum for different lines at different regions in the striations in a manner apparently connected with the excitation energies for the lines.

Societies and Academies

Societies and Academies

On experiments relating to the spectrum of nitrogen

It is somewhat remarkable that the spectrum of the neutral nitrogen atom, nitrogen arc or NI spectrum, should be the least known of the spectra associated with nitrogen. The positive and negative band spectra, associated with nitrogen molecules, have been the subject of many investigations, and the line spectra which are developed when condensed discharges are passed rough nitrogen at atmospheric pressure or through nitrogen contained in ancuum tubes, the spectrum of singly ionised nitrogen, the NII spectrum, has recently been arranged in series by Fowler ( ‘Roy. Soc. Proc.,' vol. 107, A, p. 31,25), who has in an earlier investigation (‘Monthly Notices R. A. S.,’ vol. 80, 692, 1920) assigned a number of lines which have not yet been arranged in series to the doubly ionised nitrogen atom. It would appear that under ordinary conditions of excitation the lines of the arc or nitrogen I spectrum are not conspicuous, and we are indebted to Hardtke (‘Ann. der Phys.,’ vol. 3, p. 363, 1918) for the information at present available with respect to this Spectrum. Hardtke found that with discharge tubes of special construction containing nitrogen a number of lines were predominant in the spectrum of the positive rays observed in certain regions of the discharge tubes, and that the same lines were relatively enhanced in vacuum tubes of the conventional type when they were excited by condensed discharges of feeble moderate intensities. Hardtke gave approximate measurements of a Number of these lines, which he assigned to the arc spectrum. In a series of previous investigations (Merton, ‘ Roy. Soc. Proc.,’ A, vol. 96, 382, 1920; Merton and Barratt, ‘ Phil. Trans.,’ A, vol. 222, p. 369, 1922; Merton and Johnson, ‘ Roy. Soc. Proc.,’ A, vol. 103. p. 383, 1923) it has been Shown that profound modifications are sometimes observed in the spectrum of a substance when a very small quantity of that substance is present in a discharge tube containing helium at a comparatively high pressure, and the tube is excited by condensed or uncondensed discharges. Thus with uncondensed discharges there is a striking change in the distribution of intensity the lines of the secondary spectrum of hydrogen; a trace of carbon is recognised by the appearance of the ‘‘comet tail” spectrum, first observed by Fowler (‘Monthly Notices R. A. S.,’ vol. 70, p. 484, 1910) at very low pressures and when both carbon and hydrogen are present a new triplet series of band: are developed.

Spectral Series in the Oxygen Group

IN the spectrum of oxygen there occur two types of series,—triplet series, and the so-called “singlet” series. The terms associated with the former type are designated by Fowler (“Report on Series in Line Spectra”) as ms, mp, and md, while those associated with the latter type are designated as mS, mP, and mD.

Societies and Academies

LONDON Royal Society, March 23.—Sir Charles Sherrington, president, in the chair.—Sir Richard Glazebrook: Specific heats of air, steam, and carbon dioxide. The values for the specific heats of these gases below 1000° C. given recently by Womersley are higher by 5-10 per cent, than those which follow from the results given by Holborn and Henning.—A. E. H. Tutton: (1) Monoclinic double selenates of the manganese group. The manganese group of double selenates of the isomorphous series R2Mn(SeO4)2.6H2O includes only three salts, those in which R is rubidium, cassium, and ammonium. Optically these salts are precisely in line with those for analogous salts of other groups, so that if the potassium salt could be obtained, it would be the first member of a progressive series, and the general law of progression of the crystallographic properties with the atomic number of the alkali metal would be obeyed rigidly. The volume and edge-dimensions of the space-lattice cells of the crystal structures of ammonium manganous selenate hexa-hydrate and rubidium manganous selenate are nearly identical. Similar facts obtain for all analogous ammonium and rubidium salts throughout the whole isomorphous series, as well as for the rhombic simple sulphates themselves. (2) Monoclinic double selenates of the cadmium group. Crystals of the ammonium salt, (NH4)2Cd (SeO4)2 6H2O, which were sufficiently transparent in parts for optical use were obtained on very keen frosty nights. The potassium salt appears to be incapable of existence, its limit being probably below o° C. Crystals of the rubidium or caesium salt were obtained during the coldest nights of January, but they were quite opaque, so that only goniometrical measurements were possible. The results are in complete accord with those from other, complete groups.—F. A. Freeth: The system: Na2O—CO2—NaCl—H2O. The system is arbitrarily considered as composed of two four-component systems, namely:—Na2CO3—NaHCO3—NaCl—H2O, and Na2CO2—NaOH—NaCl—H2O. Determinations have been made at 0°, 15°, 20°, 25°, 30°, 35°, 45°, and 60° C. A general treatment is given showing how the composition and quantities of the stable phases from any mixtures of the components may be deduced.- M. A. Catalán: Series and other regularities in the spectrum of manganese. Flame-arc, arc and spark spectra of manganese have been observed and new series lines traced. Series belonging to the spectrum of the neutral atom are (a) a system of triplet series; (b) a system consisting of narrow triplets; and (c) a system of narrower triplet series running parallel to the preceding system. Intercombination lines between the two first systems appear as two lines very prominent at low temperatures. The calculated ionisation and resonance potentials of manganese are 7.4 volts and 2.3 volts. Diffuse triplets in the spectrum of the ionised atom are composed of nine lines. At different temperatures, groups of lines of the same character and related by very exact numerical separations (“multiplets”) have been identified. The neutral atom of manganese probably has two electrons in the outermost ring, and when it loses one electron and becomes ionised, another electron comes out to the ring. Thus, the spectra of neutral and ionised atoms would be similarly constituted in accordance with observations.—D. W. Dye: Calculation of a standard of mutual inductance and comparison of it with the similar laboratory standard. The windings of the primary helices and the secondary overwound coil of a Campbell type of mutual inductance standard were measured in terms of the length standards of the N.P.L. and the value in absolute millihenries has been calculated. Comparisons with the similar laboratory standard at a frequency of ten cycles per second showed that the ratio of the calculated values of the two standards was in agreement with the ratio of the experimentally compared values to an accuracy of 5 in 106.—P. E. Shaw and N. Davy: The effect of temperature on gravita-tive attraction. Results with a torsion balance of the Boys-Cavendish type indicated a temperature effect of gravitation of about 1 × 10-5 per 1° C. With similar apparatus modified to eliminate small mechanical movements caused possibly by the raising of the large gravitative masses to a high temperature, the effect was shown to be due to such movements reversible with temperature. The temperature effect, if any, must be less than 2 × 10-6 per 1° C. The mean effect observed is a very small diminution in attraction as temperature rises.