Mercury Spectrum Research Articles

Anomalous Behaviour of Methane in the Raman Effect

DICKINSON, Dillon and Rasetti,1 who examined the Raman spectrum of methane, did not report the presence in it of any pure rotational lines accompanying the Rayleigh scattering. To decide whether indeed the rotational scattering is absent in the case of this gas, spectrograms were obtained by giving prolonged exposures up to a week, but without recording even a trace of such scattering by way of either discrete lines or unresolved bands alongside the undisplaced lines of the mercury spectrum. Special devices for eliminating stray light and weakening the Rayleigh scattering with the aid of a nicol were employed in order to secure the most favourable conditions for the observation, but these made no difference to the result stated.

Emission Bands in the Mercury Spectrum under Low Excitation

Emission Bands in the Mercury Spectrum under Low Excitation

Emission Bands in the Mercury Spectrum under Low Excitation

SOME years ago I found a long series of diffuse bands from λ2943 to λ2614 in the absorption spectrum of a long column of mercury vapour.1 The same series was found independently and about the same time by Mohler and Moore.

Mercury Band System in the Neighbourhood of the Resonance Line

A BAND in the mercury spectrum referred to as 2540 has been the subject of much discussion, owing to its proximity and apparent relationship to the resonance line 2536.52, and to the fact that it is seen in absorption by unexcited mercury vapour of suitable density. I have long suspected that this is only one feature of a complicated band system in this neighbourhood. The investigation is much embarrassed by the glare of the resonance line, which makes it difficult to photograph delicate details in the immediate vicinity.

The Raman spectra of some organic halogen compounds

The Raman spectra of organic compounds have recently been the subject of investigation in many laboratories. As yet, however, only a few organic halogen compounds have received attention. It was considered that a detailed investigation of several compounds of this class would throw light on fundamental questions concerning the Raman effect. Some 17 halogen derivatives of the aliphatic and aromatic hydrocarbons were accordingly investigated by the authors and the results are described in this paper. The experimental arrangements are those recommended by R. W. Wood. The accompanying tables show the analysis of the Raman lines. Under the column ∆ v are given the differences between the wave-numbers of Raman lines and the exciting lines of the mercury spectrum λ. Å. U. 3650·1, 3654·8, 3663·3, 4046·6, 4077·8, 4339·2, 4347·5, 4358·3, 5460·7, 5769·5, and 5790·5 repre­sented by the letters a , b , c , d , e , f , g , h , k , l and m respectively. Those Raman lines which happen to coincide with the incident lines of the mercury spectrum are not included in the tables.

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.

Voltage-intensity relations of 29 lines of the mercury spectrum

Voltage-intensity relations of 29 lines of the mercury spectrum

Voltage-Intensity Relations in the Mercury Spectrum

Voltage-intensity curves have been obtained for twenty lines of the mercury spectrum, when excited by electron impact. The range of accelerating voltage was from excitation to fifty volts, the discharge tube being designed to eliminate most of the disturbance due to positive ion formation. The components of four of the triplet groups were resolved and investigated separately. No significant change appears in the number of atoms in a given energy state as the ionization potential is passed. The components of each of the $\mathrm{dD}$ groups of energy levels are excited at practically the same voltage but have quite different excitation functions. The excitation functions for ${d}_{1}$, ${d}_{3}$, and $s$ levels and for the $2{p}_{2}$ level appear to be similar in form and to have sharp maxima within a few volts of the excitation voltage. The excitation functions for ${d}_{2}$ and $D$ levels also appear similar, increasing uniformly to 30 or 40 volts where they have broad maxima. The voltage-intensity characteristics of lines originating in transitions down from the same initial level agree in type but sometimes show certain differences in shape. It appears that the probability of different transitions down from a given energy state may not be independent of the way in which this state is excited. There is evidence that a large number of excitations of $2{p}_{2}$ by transitions down from higher levels are not followed by $1S\ensuremath{-}2{p}_{2}$ transitions.

The line spectrum of mercury in absorption. Occurrence of the “forbidden” line λ 2270 1 1 S 0 — 1 3 P 2

The mercury line 1 1 S 0 — 1 3 P 2 , which is forbidden by the selection rule for inner quantum numbers, has none the less been observed to occur in emission under certain special conditions. It has not been observed in the spectrum of the ordinary mercury lamp, but Takamine and Fukuda* have observed it in the spectrum of a “branched arc ” in which a small fraction of the current of a mercury vacuum arc was taken off from a supplementary anode. The line was very faint compared with the resonance line 1 1 S 0 — 1 3 P 1 or other strong lines of the mercury spectrum. I have myself observed it in the excited vapour (afterglow) from a low-current discharge of 1/10 milliampere.

Series of emission and absorption bands in the mercury spectrum

In a recent paper some remarkable phenomena exhibited by the mercury band spectrum in emission were described. In particular it was shown that the band spectrum was intimately related to the resonance line 1 1 S 0 — 1 3 P 1 (2537) and the “forbidden” lines 1 1 S 0 — 1 3 P 0 (2656) and 1 1 S 0 — 1 3 P 2 (2270) which appear strongly with it, in spite of the apparent violation of the inner quantum number rule which this implies. A system of emission bands was described, extending from λ 3055 to λ 2697, with the spacing diminishing from 21 A to about 6 A. The starting point of the present investigation was to look for these bands in absorption, so as to determine whether they had for their lower energy level one associated with the normal state of the molecule.

Relative Intensities of Some Lines in the Mercury Spectrum

Intensities of the most intense spectrum lines associated with transitions to and from the $2{p}_{2}$ state in mercury were measured by means of a photographic method. The spectrum of the vapor was excited by electron impact above the ionization potential. Variations in the line intensities due to changes in the accelerating potentials and vapor pressures were observed. At 22\ifmmode^\circ\else\textdegree\fi{}C and with 50 volt electrons, there were about 1.7\ifmmode\times\else\texttimes\fi{}${10}^{12}$ quanta of $\ensuremath{\lambda}2537$ radiation emitted per cubic centimeter per second for a current density of 4.75\ifmmode\times\else\texttimes\fi{}${10}^{15}$ electrons per square centimeter per second. From the intensities of the other lines relative to $\ensuremath{\lambda}2537$, it was found that there are apparently more transitions to $2{p}_{2}$ than down from $2{p}_{2}$, as given by measurements of the radiation. This made it impossible to determine the probability of excitation of resonance from the intensities of the spectrum lines. A comparison is made between the relative intensities in the experimental tube and in a commercial arc.

Voltage-Intensity Relations of Mercury Lines Below Ionization

Accelerating voltage-intensity relations have been obtained for twenty-eight lines of the mercury spectrum (between 5500A and 2500A) excited by electronic bombardment at potentials less than the ionization potential. The tube in which the radiation was excited had four electrodes, hot cathode and three grids, and the observations were made by photographic spectrophotometric measurements. In agreement with the results of other workers, the minimum potential of excitation of a line is found to agree closely with the theoretical value in all cases but one. The curves representing the voltage-intensity relation for lines with a common outer orbit are found identical when the intensity scales are so chosen as to arbitrarily make the curves coincide at one point. Upward and downward breaks are found in these curves at certain critical potentials but the character of the breaks and the potentials at which they occur change from series to series. The ratio of the numbers of quanta emitted in the lines of the triplet $2{p}_{1}\ensuremath{-}2s(5461)$, $2{p}_{2}\ensuremath{-}2s(4358)$, $2{p}_{3}\ensuremath{-}2s(4047)$ with an accelerating voltage of 10.2 volts was found to be 9:11:3.

On the excitation of polarised light by electron impact

In the course of some experiments on polarisation effects shown by mercury lines, emitted from a low-pressure electron-maintained arc, it was found that the yellow mercury lines λ 5770, 5791 are weakly polarised even in the absence of a magnetic field, the direction of the maximum electric vector being parallel to the direction of the discharge. From the general characteristics of the effect, it appeared likely that the polarisation is due to the partly directed character of the electron tracks in the arc; and, in this way, one was led to the view that an electron is capable of exciting an atom to the emission of polarised light. The present paper describes an attempt to investigate this point more thoroughly. While the work was in progress, two papers have appeared in which a search for signs of polarisation in the light excited by electron impact has been made. The first is by Kossel and Gerthsen who examined the case of the D lines of Sodium with a negative result. This was confirmed by Ellett, Foote and Mohler, who also investigated the case of the mercury line λ 2537 with a positive result, which will be described subsequently. These experiments, however, only dealt with a few individual spectral lines. In the present work data have been obtained for all the more prominent lines of the mercury Spectrum.

The Effect of Helium on the Intensity of the Mercury Spectrum

The Effect of Helium on the Intensity of the Mercury Spectrum

On the Polarised Emission of Mercury Lines

EXPERIMENTS are in progress in which the mercury spectrum is excited by a directed stream of electrons from an oxide coated filament, and the polarisation of the lines examined. The track of the electron beam in a field-free space at a pressure of 1/1000th mm. is well defined, and little visible light is emitted from points not in the path of the electrons. Accelerating voltages of 30–40 volts have mainly been used, and the light from the stream is observed at right angles to its direction. Under these conditions a number of p-d combinations are polarised, the plane of polarisation being with the maximum electric vector parallel to the stream. The plane of polarisation rotates with the tube and so cannot be governed by any stray field.

LXXXII. Optical excitation of the mercury spectrum, with controlled orbital transfers of electrons

LXXXII. <i>Optical excitation of the mercury spectrum, with controlled orbital transfers of electrons</i>

Societies and Academies

LONDON. Royal Society, November 2.—Sir Charles Sherrington, president, in the chair.—Lord Rayleigh: Polarisation of the light scattered by mercury vapour near the resonance periodicity. White light scattered at right angles by dense mercury vapour is to a first approximation completely polarised. Ultra-violet radiation of the mercury spectrum line λ2536, when examined immediately it enters mercury vapour in an exhausted vessel at room temperature, gives a scattered radiation which is slightly though definitely polarised. This polarisation has been observed to increase as the beam is filtered by penetration of a considerable depth of vapour. After penetration of 27.5 cm. of vapour the weaker polarised image had 6o per cent, only of the intensity of the stronger one, instead of 90 per cent. as at first. The radiation removed by the filtration appears to lie within a spectral range of about 1/100 Ångstrom.—G. P. Thomson: The scattering of hydrogen positive rays and the existence of a powerful field of force in the hydrogen molecule. At a pressure of less than 1/100 mm., hydrogen positive rays of 10,000 volts mean energy suffer considerable small-angle scattering in a distance of cm. This scattering is 10.20 times greater than would be expected on theoretical grounds. There must, therefore, be a field of force in the hydrogen molecule at distances of the order of io from a nucleus which is much stronger than would be expected from the inverse square law. A subsidiary experiment throws great doubt on Glimme and Koenigsberger's “Stossstrahlen.”-H. D. Smyth: A new method for studying ionizing potentials. Positive ray analysis is used to study the ions produced in a gas or vapour by the impact of slow- speed electrons of known energy. This requires that the density of gas be considerable where the energy of the impacting electrons is known, and as small as possible where the energy conditions are not known. In the case of mercury such a localisation of vapour density was obtained by using a unidirectional molecular stream similar to that employed in a mercury diffusion pump. Ions were produced by electrons from a hot filament, and after acceleration by a large electric field were analysed by a magnetic field. In this way the values of me were determined approximately. The experiments on mercury indicate the formation of doubly charged ions at 19+2 volts.

The Normal Orbit of the Electron in the Atom of Mercury

RESEARCHES on ionisation and resonance potentials of mercury vapour and on its ultra-violet absorption in a non-luminous state, together with considerations from the serial type of the mercury spectrum, lead to the definite conclusion that in the absence of exciting agencies the spectral electron remains on the orbit 1S, the normal orbit of the atom of mercury. On the other hand, R. Dearle has shown the presence of a strong infra-red absorption band at λ=10140, and this fact has suggested the possibility of a second normal orbit in the mercury atom, namely, the orbit 2P. The corresponding ionisation and resonance potentials have, however, never been observed. This: problem induced us to make an absorption experiment with non-luminous mercury vapour in the infra-red region, using a photographic method which enabled us easily to reach λ=11300 Å. All the photographs showed complete absence of a marked absorption at λ=10140, although the pressure of mercury vapour reached 1 atm. The efficiency of the method having been established, the absence of a strong and characteristic absorption of λ=10140 by mercury vapour has been shown and the necessity for a second normal orbit is avoided.

XXX. The limiting frequency in the spectra of helium, hydrogen, and mercury in the extreme ultra-violet

Summary The most important results of this investigation may be summarized as follows:— The high frequency limits of the spectra of helium, hydrogen, and mercury when stimulated by large electron currents under potentials up to about 800 volts have been determined. The measurements are believed to be most accurate for helium and least accurate for mercury. The helium spectrum extends to a limit which is certainly between 470 and 420 and probably near to the latter value. The hydrogen spectrum terminates at a wave-length between 830 and 950 Ångström units and probably close to 900. The mercury spectrum terminates at a wave-length between 1000 and 1200 Åström units. So far as we are able to ascertain, the observed terminal frequencies are identical with the frequencies calculated from Bohr's theoretical values of the ionization potentials of the respective gases, and they exhibit no obvious relationship to the ionization potentials which have been determined experimentally by Franck and Hertz and others. The ultra-violet spectrum has been extended to a wave-length which is certainly shorter than 470 and probably close to 420 Ångström units. The high frequency limits of the spectra referred to are independent of the applied potential up to about 800 volts, provided this potential exceeds a lower limit which has not been determined with any accuracy.

X.—On a Possible Explanation of the Satellites of Spectral Lines

It is well known that, when examined with a modern high-power spectroscope, the bright lines in the spectra of the different elements exhibit an individual character. Some are diffuse, some are sharp, some are diffuse on the one side and sharp on the other, and some are accompanied by fainter lines in their neighbourhood. To the latter the name of satellites has been given. The most celebrated satellites are those of the green line of mercury, which have been investigated very often owing to the ease with which the mercury spectrum can be produced. They are much fainter than the main line, and at least six can be seen. But there are cases occurring in which a satellite is so strong that it is hardly possible to say which is the main line. Thus the red line of hydrogen is a close doublet with a separation of ·14 A.U., the two components of the doublet being of approximately equal brightness.