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Physical Review

The Influence of the Method of Excitation on Transition Probabilities in Sodium Vapor

Carl J. Christensen, G. K. Rollefson

Published Oct 15, 1929• 6 citations
Publisher

Abstract

Fluorescence has been excited in sodium vapor at 180\ifmmode^\circ\else\textdegree\fi{}C by illuminating with the second member of the principal series, $\ensuremath{\lambda}=3303\mathrm{A}$. Both the first and second members of the principal series appeared in the fluorescence, the first member being due to the atom returning to its normal state in steps. The ratio of the intensities of the two lines was determined by photographic photometry and the results compared with what might be expected on the basis of measurements by Weiss on the sodium arc. In the arc the atom returns to the normal state from the $3P$ by way of the $2S$ twentyfive times as often as the direct transition occurs whereas in fluorescence approximately the same number take each path. This is contrary to the usual assumption that the transition probabilities are independent of the method of excitation.

DOI
10.1103/physrev.34.1157

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Transition Probabilities and Quenching in the 3P State of Sodium

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The effect of foreign gases upon the fluorescence of sodium vapor excited by the second line of the principal series has been investigated. The gases used were helium, nitrogen, and hydrogen and the intensities of both the 3303A line and the $D$ light were observed. From the variation in intensity of the 3303A line as gas is added it is concluded that the presence of an inert gas has no appreciable effect upon the relative transition probabilities in the ${3}^{2}P$ state of sodium. With nitrogen or hydrogen as the added gas the $D$ light intensity variation followed that of the 3303A line very closely but with helium a marked increase in intensity was produced by the first gas added with a decrease at higher pressures. This increase was explained as due to a transfer of sodium atoms from the ${3}^{2}P$ to the ${3}^{2}D$ state by collisions, thus increasing the number of atoms which radiate the $D$ light. In addition to this increase in number the collisional transfers produced an increased "Doppler width" in the $D$ light which persisted up to pressures well over 100 mm of helium and caused a decreased absorption of the fluorescence light. The bearing of this work on the difference in the intensity ratio of the ${2}^{2}S\ensuremath{-}{3}^{2}P$ and ${1}^{2}S\ensuremath{-}{3}^{2}P$ transitions as reported by Weiss for an arc and by Christensen and Rollefson in fluorescence is discussed. It is concluded on the basis of experimental evidence that any explanation of the difference which depends upon multiplicity of the ${3}^{2}P$ state is incorrect. An explanation of this difference based upon the assumption that the life period of an excited atom varies inversely as the transition probability of the radiation emitted is presented. It is shown that recent work on the life periods of atoms in the ${2}^{3}{S}_{1}$ state of mercury at least partially supports this assumption. A new type of sodium arc with increased intensity and stability of operation is described.

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TPHE purpose of this investigation was to study the resonance spec--*-trum of sodium vapor when the resonance was excited by a single D line.In a paper on " Resonance Radiation of Sodium Vapor "* published by one of us in 1905, it was shown that if a bulb containing pure sodium vapor was illuminated by light from a sodium flame, the vapor emitted a yellow light which spectroscopic analysis showed to be identical with the exciting light, in other words, the two D lines.It was suggested at this time that it would be interesting to see if both D lines appeared when the vapor was illuminated by a single D line.This would determine whether the mechanisms that give rise to the D lines are separate or in some way connected.In 1914 this experiment was tried by Wood and Dunoyer. 2 This experiment was made possible by the discovery of a polarization method of separating close spectral doublets that eliminated the great loss of light involved in a high-power monochromator, but even with this method the resonance light is very faint.The spectrum of resonance excited by D 2 was photographed with exposures varying from 10 to 15 hours.The majority of the plates showed only the D 2 line, but owing to under exposure Di would not have been visible if it was less than one fourth of the intensity of D 2 .Some plates indeed showed both Di and D 2 , but the presence of Di in the exciting light was judged to be the cause of this.Imperfections in the optical system made it impossible to entirely remove Di from the exciting light and as it was sensitive to temperature changes the nature of the transmitted light sometimes changed during an exposure.It was concluded that sodium resonance excited by D 2 consisted of D 2 alone, but the results admit of two other possibilities.Di light may always be present though much fainter than D 2 , or it may only appear under certain conditions.Other resonance phenomena show that the radiation centers in sodium are not entirely independent.One of us 3 showed in 1905 that excitation 1

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Inelastic collisions between excited alkali atoms and molecules. V. Sensitized fluorescence in mixtures of sodium with N2, H2, HD, and D2

M. Stupavsky, L. Krause

3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, induced in inelastic collisions with ground-state N2, H2, HD, and D2 molecules, has been investigated in a series of sensitized fluorescence experiments. Mixtures of sodium vapor at a pressure of 5 × 10−7 Torr, and the gases, were irradiated with each NaD component in turn, and the fluorescence which contained both D components was monitored at right angles to the direction of the exciting beam. Measurements of the relative intensities of the NaD fluorescent components yielded the following collision cross sections for excitation transfer. For Na–N2 collisions: Q12(2P1/2 → P3/2) = 144 Å2, Q21(2P1,2 ← 2P3/2) = 76 Å2 for Na–H2 collisions: Q12 = 80 Å2, Q21 = 42 Å2. For Na–HD collisions: Q12 = 84 Å2, Q21 = 44 Å2. For Na–D2 collisions: Q12 = 98 Å2, Q21 = 52 Å2. The cross sections Q21 exhibit a slight resonance effect between the atomic and molecular rotational transitions.

Canadian Journal of Physics•Oct 1, 1968•23 citations
Fluorescence has been excited in sodium vapor at 180\ifmmode^\circ\else\textdegree\fi{}C by illuminating with the second member of the principal series, \ensuremathλ=3303A\ensuremath{\lambda}=3303\mathrm{A}\ensuremathλ=3303A. Both the first and second members of the principal series appeared in the fluorescence, the first member being due to the atom returning to its normal state in steps. The ratio of the intensities of the two lines was determined by photographic photometry and the results compared with what might be expected on the basis of measurements by Weiss on the sodium arc. In the arc the atom returns to the normal state from the 3P3P3P by way of the 2S2S2S twentyfive times as often as the direct transition occurs whereas in fluorescence approximately the same number take each path. This is contrary to the usual assumption that the transition probabilities are independent of the method of excitation.
The effect of foreign gases upon the fluorescence of sodium vapor excited by the second line of the principal series has been investigated. The gases used were helium, nitrogen, and hydrogen and the intensities of both the 3303A line and the DDD light were observed. From the variation in intensity of the 3303A line as gas is added it is concluded that the presence of an inert gas has no appreciable effect upon the relative transition probabilities in the 32P{3}^{2}P32P state of sodium. With nitrogen or hydrogen as the added gas the DDD light intensity variation followed that of the 3303A line very closely but with helium a marked increase in intensity was produced by the first gas added with a decrease at higher pressures. This increase was explained as due to a transfer of sodium atoms from the 32P{3}^{2}P32P to the 32D{3}^{2}D32D state by collisions, thus increasing the number of atoms which radiate the DDD light. In addition to this increase in number the collisional transfers produced an increased "Doppler width" in the DDD light which persisted up to pressures well over 100 mm of helium and caused a decreased absorption of the fluorescence light. The bearing of this work on the difference in the intensity ratio of the ${2}^{2}S\ensuremath{-}{3}^{2}P$ and ${1}^{2}S\ensuremath{-}{3}^{2}P$ transitions as reported by Weiss for an arc and by Christensen and Rollefson in fluorescence is discussed. It is concluded on the basis of experimental evidence that any explanation of the difference which depends upon multiplicity of the 32P{3}^{2}P32P state is incorrect. An explanation of this difference based upon the assumption that the life period of an excited atom varies inversely as the transition probability of the radiation emitted is presented. It is shown that recent work on the life periods of atoms in the 23S1{2}^{3}{S}_{1}23S1​ state of mercury at least partially supports this assumption. A new type of sodium arc with increased intensity and stability of operation is described.
A mixture of potassium vapor and mercury vapor contained in a tube fashioned after the Cario-Lochte-Holtgreven sodium vapor lamp was radiated by light from a water-cooled mercury arc. The resulting fluorescence radiation contained potassium lines as well as two of the three known K2{\mathrm{K}}_{2}K2​ absorption bands and a new band with maximum at 5721A. On exposure of the mixture to light from a hot mercury arc or to light having all wave-lengths shorter than 2800A filtered out, the fluorescence was eliminated. This indicated that the excitation was caused by absorption of 2536A by the mercury. Absorption of the 2536A mercury line raises the mercury atom to the 63P16^{3}P_{1}63P1​ state, having an energy of 4.86 volts. The ionization potential of potassium is 4.32 volts; thus in a collision of the second kind, the excited mercury atom has enough energy to ionize the potassium atom. There was no evidence of a potassium emission from an energy state in the continuum equal in energy to the Hg 63P16^{3}P_{1}63P1​ or 63P06^{3}P_{0}63P0​ states. There were, however, two strong lines in fluorescence which could not be ascribed to the usual K energy levels nor to any probable impurity. To test whether or not ionization of potassium actually takes place, a filament was introduced into the tube to supply electrons. A large increase in intensity of the fluorescence of potassium lines was obtained with the hot filament. It was furthermore found that the intensity increased with filament temperature.
The intensity ratio D2/D1 for the sodium doublet has been measured for radiation from excited sodium atoms which result from the optical dissociation of sodium iodide vapor by ultraviolet light in the 2082→2500 A region. With shorter wavelength ultraviolet light as exciting source, the D2/D1 ratio is 0.98 and increases to above 1.5 with longer exciting wavelengths. Addition of foreign gases cause the observed D2/D1 ratio to increase to 1.89 for large foreign gas pressure. Cross sections for the transfer of excited sodium atoms from the 32P32 to the 32P½ state and vice versa due to collisions with foreign molecules have been measured as they depend on the relative velocity between excited sodium atom and foreign molecule. The Doppler broadening of the separate D lines emitted in the atomic fluorescence of sodium iodide has been estimated from absorption measurements. Both lines show equal broadening within the experimental error of the observations. Measurements were made with a photomultiplier tube. The sodium doublet was resolved with a reflection grating monochromator.
TPHE purpose of this investigation was to study the resonance spec--*-trum of sodium vapor when the resonance was excited by a single D line.In a paper on " Resonance Radiation of Sodium Vapor "* published by one of us in 1905, it was shown that if a bulb containing pure sodium vapor was illuminated by light from a sodium flame, the vapor emitted a yellow light which spectroscopic analysis showed to be identical with the exciting light, in other words, the two D lines.It was suggested at this time that it would be interesting to see if both D lines appeared when the vapor was illuminated by a single D line.This would determine whether the mechanisms that give rise to the D lines are separate or in some way connected.In 1914 this experiment was tried by Wood and Dunoyer. 2 This experiment was made possible by the discovery of a polarization method of separating close spectral doublets that eliminated the great loss of light involved in a high-power monochromator, but even with this method the resonance light is very faint.The spectrum of resonance excited by D 2 was photographed with exposures varying from 10 to 15 hours.The majority of the plates showed only the D 2 line, but owing to under exposure Di would not have been visible if it was less than one fourth of the intensity of D 2 .Some plates indeed showed both Di and D 2 , but the presence of Di in the exciting light was judged to be the cause of this.Imperfections in the optical system made it impossible to entirely remove Di from the exciting light and as it was sensitive to temperature changes the nature of the transmitted light sometimes changed during an exposure.It was concluded that sodium resonance excited by D 2 consisted of D 2 alone, but the results admit of two other possibilities.Di light may always be present though much fainter than D 2 , or it may only appear under certain conditions.Other resonance phenomena show that the radiation centers in sodium are not entirely independent.One of us 3 showed in 1905 that excitation 1
The sodium D2{\mathit{D}}_{2}D2​ transition is resonantly excited by \ensuremath{\pi}-polarized, narrow-band laser radiation. The line polarization of the resulting fluorescence detected normally to the plane containing the electric-field vector of the radiation and its propagation direction, as well as the atomic beam, is measured as a function of radiation intensity and tuning. The data are compared to calculations from a quantum-electrodynamic theory which includes all participating energy states in the hyperfine representation. The quantitative agreement is very good.
3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, induced in inelastic collisions with ground-state N2, H2, HD, and D2 molecules, has been investigated in a series of sensitized fluorescence experiments. Mixtures of sodium vapor at a pressure of 5 × 10−7 Torr, and the gases, were irradiated with each NaD component in turn, and the fluorescence which contained both D components was monitored at right angles to the direction of the exciting beam. Measurements of the relative intensities of the NaD fluorescent components yielded the following collision cross sections for excitation transfer. For Na–N2 collisions: Q12(2P1/2 → P3/2) = 144 Å2, Q21(2P1,2 ← 2P3/2) = 76 Å2 for Na–H2 collisions: Q12 = 80 Å2, Q21 = 42 Å2. For Na–HD collisions: Q12 = 84 Å2, Q21 = 44 Å2. For Na–D2 collisions: Q12 = 98 Å2, Q21 = 52 Å2. The cross sections Q21 exhibit a slight resonance effect between the atomic and molecular rotational transitions.