Secondary Spectrum Of Hydrogen Research Articles

XIV. Note on the secondary spectrum of hydrogen

XIV. <i>Note on the secondary spectrum of hydrogen</i>

The Secondary Spectrum of Hydrogen

THE recent investigation by Dr. Merton of the effect of an admixture of helium on the intensity distribution in the hydrogen spectrum appears to have given a very strong clue towards the elucidation of that spectrum. On the photographs taken by Dr. Merton (reproduced in part in Proc. Roy. Soc, October, 1919) the spectra appear completely different in the cases of pure hydrogen and of hydrogen mixed with helium. Many lines, in the first case quite strong, are totally absent in the second; others remain practically unaltered in intensity; while a third set appears in the second case, though practically or completely invisible in the first. Such results seem, at first sight, to point to the existence of at least three classes of lines which are mutually independent, one class being unaffected by helium and the others affected in opposite senses.

On the secondary spectrum of hydrogen

Theoretical investigations of the origin of spectra in relation to the structure of the atom have concentrated especially on the spectrum of hydrogen, on account of the supposed simplicity of the hydrogen atom. They have, however, been confined almost exclusively to the Balmer series, and have ignored the difficulties which arise from the fact that hydrogen possesses another spectrum, usually known as the secondary spectrum, which is of great complexity, and the co-ordination of whose lines into recognised bands or series of lines is still in a very unfinished state. The investigations of Buisson and Fabry, in which the physical widths of spectrum lines were measured with the interferometer, refer at least a part of the lines of the secondary spectrum to the hydrogen atom, and the complications introduced into theoretical investigations cannot therefore be impartially waived by the assumption that the molecule is concerned in the production of the secondary spectrum. As regards the relation of the two spectra, there is abundant evidence of a fundamental difference in their origin. In many celestial spectra the lines of the Balmer series constitute one of the most prominent features, whilst the identification of lines of the secondary spectrum is at least extremely doubtful. In the laboratory it has long been known that the relative intensity of the secondary spectrum is greatly reduced by the presence of impurities, notably oxygen, in vacuum tubes containing hydrogen, and by the passage of powerful condensed discharges. On the other hand, under conditions in which an uncondensed discharge from an induction coil is passed through very dry and pure hydrogen at a reduced pressure, the lines of the secondary spectrum may rival those of the Balmer series in intensity.

Societies and Academies

LONDON. Royal Society, December 4.—Sir J. J. Thomson, president, in the chair.—A. M. Williams: The adsorption 'of gases at low and moderate concentrations. Part i.: Deduction of the theoretical adsorption iso-stere and isotherm. Part ii.: Experimental verification of the form of the theoretical isosteres and isotherms.—A. M. Williams: The adsorption of gases at low and moderate concentrations. Part iii.: Experimental verification of the constant in the theoretical adsorption isostere.—T. R. Merton: The secondary spectrum of hydrogen. It has been found that the presence of a large quantity of helium in vacuum tubes containing hydrogen modifies the secondary hydrogen spectrum in the sense that the relative intensities of the lines are completely altered, some lines being extremely weak in the spectrum of the mixture, whilst others are greatly enhanced and a number of new lines appear. Measurements have been made of the lines which are enhanced or unaffected by the admixture of helium; the changes are shown in a reproduction of a photograph of the two spectra in juxtaposition with a wave-length scale, by means of which the lines which are weaker in the spectrum of the mixture can be identified by reference to Watson's measurements of the spectrum. The secondary hydrogen spectrum is of such complexity that the segregation of its lines into series of mathematically related lines is a task which offers great difficulties. These difficulties can doubtless be lessened by the aid of physical methods of separating the lines into different classes.—T. R. Merton: The spectra of isotopes, (1) Interferometer measurements of the principal line in the spectrum of ordinary lead and lead from pitchblende show that in the latter case the line is less refrangible by 0.0050 A. ±0.0007 A., in close agreement with the results of Aronberg. (2) In the case of lead from Ceylon thorite it has been found that the line is more refrangible than in ordinary lead by 0.0022 A. ± 0.0008 A. (3) The positions of the lines are arranged in the order of their atomic weights. (4) Spectro-scopic measurements seem to provide a favourable method of distinguishing isotopic elements. (5) A comparison has been made of the wave-lengths of the principal line in ordinary thallium1 and thallium from pitchblende residues. The wave-length of the line in the spectrum of thallium from pitchblende has been found to be more refrangible than the line in ordinary thallium by 0.0055 A. ±0.0010 A. In the case of thallium the measurements may possibly be affected by certain disturbing factors which do not apply to the measurements of the lines of lead. Unless the results are affected by these disturbing factors, it would seem likely that the thallium in pitchblende is an isotope of ordinary thallium.—E. F. Armstrong and T. P. Hilditch: A study of catalytic actions at solid surfaces. Part ii. It is shown that the catalytic action of metals, like that of certain enzymes, is reversible; in other words, compounds which are saturated in the ordinary sense are capable of interacting with the metal to form a system which breaks down into a more stable equilibrium consisting of hydrogen and a less saturated compound. This is readily demonstrated in the case of cyclohexanol; when a mixture of cyclohexanol and methyl cinnamate' is heated at 180° in presence of nickel, a considerable transference into cyclohexanone and methyl β-phenyl propionate is effected. It is necessary that both components of the system should be present in the liquid state. Dehydrogenation has also been effected in the case of hexahydroxylene and dihydropinene mixed with methyl cinnamate in presence of nickel; in these cases a temperature of 230° is required. At this tempera'ture' small quantities of an ethyl oleate of unknown structure are obtained from ethyl stearate.—F. Horton and Ann C. Davies: An experimental determination of the critical electron velocities for the production of radiation and ionisation on collision with argon atoms. The critical velocities for electrons in argon were investigated by methods similar to those employed in a; previous research for the determination of trie corresponding values in helium, the earlier form of apparatus being modified somewhat to facilitate the detection of the beginnings of radiation and ionisation. As the result of many experiments under different conditions, the values 11.5 volts and 15.1 volts were obtained for minimum radiation velocity and minimum ionisation velocity respectively. No sudden increase of radiation at the second critical velocity was detected, and it was shown that no detectable amount of ionisation was produced at 11.5 volts, fhe limiting wavelength of the argon spectrum, calculated from the value, 15.1 volts, found for the minimum ionisation velocity, is in agreement with the limit observed spectroscopically in the recent experiments of Lyman.

X. On the distribution of intensity in broadened spectrum lines

It is a curious fact that although our knowledge of the structure of the finest spectrum lines may now be said to rest on a secure theoretical and experimental basis, little is known of the distribution of energy in the broadened spectrum lines which are produced under certain conditions of excitation, or the exact circumstances which control their broadening. The researches of Lord Rayleigh, Michelson, Buisson and Fabry, and others have shown that in gases at low pressures, when excited by uncondensed electric discharges, the width of the spectrum lines emitted can be accounted for completely and satisfactorily by the translatory motion of the radiating particles, in accordance with Doppler’s principle. Measurements of the width of such lines are carried out with the interferometer, the measurement consisting of a determination of the limiting order of interference at which fringes can he seen. This limiting order of interference is given by the equation N = K (M/T) ½ where N is the limiting order of interference, M the mass of the luminous particle in terms of the hydrogen atom, T the absolute temperature and K a constant. This equation is derived from a consideration of the Doppler effect produced by a distribution of the velocities of the radiating particles in accordance with Maxwell’s law, and its experimental verification by Buisson and Fabry shows not only that under the conditions specified the widths of the lines are completely accounted for, but also that the distribution of intensity in the lines is given by the well-known probability law. Under these conditions it is further shown that the limiting order of interference is constant for all lines and all series of the same element. Thus the same value of N is found for the helium and the parhelium series, and in the same manner for the Rainier series and lines of the secondary spectrum of hydrogen. With any departure from the specified conditions of low pressure and excitation by uncondensed electric discharge the law breaks down, and the lines broaden in an apparently anomalous manner. The characteristics which lead Rydberg to adopt the terms diffuse and sharp series appear, the higher members of a series undergoing the greater degree of broadening. Matters are complicated by the fact that the broadening is in many cases unsymmetrical, and in addition we must take into account the fact pointed out by Royds, that different members of the same series may be unsymmetrically broadened in opposite directions. Thus in the case of the first subordinate “triplet” series of barium, the members consisting of triplet and satellites at λλ 5819-5424 are all unsymmetrically broadened towards the red, whilst the members of the succeeding triplet (and satellites) and λλ 4493-4264 are unsym­metrically broadened towards the violet. Royds shows that similar phenomena occur in the spectra of calcium and strontium, and points out the importance of the phenomena in relation to the pressure shifts of the lines in question. There can be no doubt of the intimate relation between the direction of the asymmetry and the pressure shift, since it has been shown by St. John and Ware, Fabry and Buisson, and by Gale and Adams that iron lines which broaden unsymmetrically towards the red are displaced by pressure towards the red, whilst lines which are unsym­metrically broadened towards the violet are displaced by pressure towards the violet. It is well known that broadening of spectrum lines can be produced either by an increase of the pressure of the luminous gas or by the use of highly condensed discharges as a means of excitation, and although the two conditions are different he phenomena of broadening which result appear to be similar. In a previous investigation it has been pointed out by one of the authors that from a consideration of the general characteristics of the broadening it appears difficult to refer the phenomena to the movements of the luminous particles as a whole, but rather that effects more intimately connected with the problem of radiation must be concerned. A recent suggestion by Stark as to the cause of the broadening appears to be in harmony with the experimental results at present available.

On a second spectrum of neon

The spectrum of the gases of atmospheric air which were not condensed at the temperature of liquid hydrogen was first investigated by Liveing and Dewar, who found a large number of lines which did not belong to the spectra of hydrogen or helium. The spectrum of the glow from the negative pole was photographed, owing to the fact that the secondary spectrum of hydrogen was predominant in the capillary. It was found that, whilst the secondary hydrogen spectrum disappeared when a jar discharge was used, the greater part of the lines of unknown origin were also obliterated.

On the Appearance of Helium and Neon in Vacuum Tubes

SINCE reading before the Chemical Society (see NATURE, February 13, p. 653) the paper on the presence of helium and neon in vacuum tubes (containing hydrogen) after the gas had been sparked, we have carefully compared the spectrum lines that are supposed to be characteristic of these gases. The result has been interesting. In the case of neon and hydrogen there appears to be a large number of lines in the secondary spectrum of hydrogen that are very close to the important lines of neon. If only those lines are taken that differ by less than a quarter of an Angstrom unit (using the measurements of Watson), there are fifty-seven instances. It is not necessary to give all of them, but if the neon lines of intensity 4 and greater be taken it is found that there are twenty instances:—

LXXX. The secondary spectrum of hydrogen

(1909). LXXX. The secondary spectrum of hydrogen. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 17, No. 102, pp. 854-855.

On the wave-lengths of lines in the secondary spectrum of hydrogen

The spectrum of hydrogen is one which has engaged the attention of numerous observers from the year 1851 onwards. Historically it is of great interest, firstly owing to the part it played in the controversy between Ångstrom and Wüllner on the plurality of spectra, and secondly, because it was the first spectrum in which a relation between the wave-lengths of the lines composing it was discovered. It is not proposed to discuss the origin of the two hydrogen spectra in this communication, as it has recently been done in a very complete manner by Dufour; the main points at issue, however, may perhaps be briefly stated.

LII. The secondary spectrum of hydrogen

(1909). LII. The secondary spectrum of hydrogen. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 17, No. 100, pp. 581-583.

The Spectrum of Radium Emanation

IN NATURE of July 9 a letter from Prof. Rutherford appears giving an excellent corroboration of measurements of the spectrum of radium emanation which we communicated to the Royal Society on July 1. There can, therefore, be no doubt of the accuracy of Prof. Rutherford's measurements. When Mr. Watson, who is engaged in measuring accurately with a 10-foot grating the secondary spectrum of hydrogen, has finished his task, we shall be able to introduce some small corrections in our figures.