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Physical Review

The Efficiency of Quenching Collisions and the Radius of the Excited Mercury Atom

Enrique Gaviola

Published Mar 1, 1929• 11 citations
Publisher

Abstract

The evidence in favor and against the assumption of Foote that every collision of a foreign gas molecule with an excited mercury atom is efficient in quenching the resonance radiation is discussed, and a new calculation of the efficiency of collisions is given, based on Stuart's measurements, which shows that the efficiency can be assumed to be equal to one in the case of CO, ${\mathrm{H}}_{2}$, and perhaps ${\mathrm{O}}_{2}$, but that it is undoubtedly smaller than one for ${\mathrm{H}}_{2}$O, ${\mathrm{N}}_{2}$, A, and He. CO has actually a greater quenching efficiency than ${\mathrm{H}}_{2}$. The radius of the excited mercury atom is calculated using an improved value for the amount of resonance-radiation re-absorbed in the resonance vessel and found to be ${r}_{{\mathrm{Hg}}^{\ensuremath{'}}}=2.91\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ cm, or 1.62 times larger than the radius of the normal atom for the case of ${\mathrm{H}}_{2}$, and ${r}_{{\mathrm{Hg}}^{\ensuremath{'}}}=5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ cm or three-fold normal for the case of CO. The apparent higher quenching efficiency of oxygen than hydrogen is explained by the partial oxidation of the mercury vapor and consequent decrease of the density of the last. It is shown that the life of metastable atoms increases with the admission of certain foreign gases into the fluorescence vessel.

DOI
10.1103/physrev.33.309

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Quenching and Depolarization of Mercury Resonance Radiation

J. S. Deech, John M. Pitre, L. Krause

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The Effect of Foreign Gases upon the Relative Intensities of the Mercury Triplet 2P0123−2S13 under Conditions of Optical Excitation

R. T. Macdonald, G. K. Rollefson

Effect of nitrogen and of mixtures of nitrogen and carbon dioxide upon the fluorescence of mercury vapor. By "stepwise" optical excitation, unexcited mercury atoms are raised to the $2^{3}S_{1}$ state. They may leave this level upon the emission of radiation by four paths---the first to the $2^{1}P_{1}$ state, a transition of relatively low probability, and the other three to the $2^{3}P_{2}$, $2^{3}P_{1}$, and $2^{3}P_{0}$ states with the emission of 5461A, 4358A and 4046A, respectively. Measurements, by totally independent methods, of the mean life of the $2^{3}S_{1}$ state yielded values, when measured by the line 5461A, equal to approximately four times those when measured by either 4358A or 4046A. Upon the addition of foreign gas, then, the intensity ratio of 5461A to either 4358A or 4046A should decrease with increasing pressure while that of 4046A to 4358A should remain constant. However, these ratios were all found to be invariant with pressure, up to 400 mm in the case of nitrogen and up to 100 mm in the case of the nitrogen-carbon dioxide mixtures.

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Effects of Added Gases on the Sensitized Fluorescence Spectrum of a Hg-Tl Mixture

Richard Allen Anderson, Robert H. McFarland

An investigation of the sensitized fluorescence of a mercury thallium mixture without and with the addition of argon and helium gases is discussed. Data taken without the addition of foreign gases are used to extend the theory of Frish and Karaulinya to a mercury thallium mixture. Relative collision cross sections for the excitation of the thallium energy states, $9^{2}S_{\frac{1}{2}}$, $7^{2}D_{\frac{5}{2},\frac{3}{2}}$, $8^{2}S_{\frac{1}{2}}$, $6^{2}D_{\frac{5}{2}}$, and $6^{2}D_{\frac{3}{2}}$ were calculated for mercury thallium collisions. Data taken with the addition of argon and helium gases are given to indicate the variation of the intensity of the thallium lines as a function of argon and helium gas pressures at one constant thallium and three mercury temperatures. The explanation of the results depends on the role of mercury $6^{3}P_{1}$ excited atoms, metastable atoms, and mercury molecules in collision with thallium atoms for energy exchange, and also requires the use of Winans' partial selection rule and other generally accepted ideas concerning energy transfer, emission, and absorption.

Physical Review•Jul 15, 1960•9 citations
The evidence in favor and against the assumption of Foote that every collision of a foreign gas molecule with an excited mercury atom is efficient in quenching the resonance radiation is discussed, and a new calculation of the efficiency of collisions is given, based on Stuart's measurements, which shows that the efficiency can be assumed to be equal to one in the case of CO, H2{\mathrm{H}}_{2}H2​, and perhaps O2{\mathrm{O}}_{2}O2​, but that it is undoubtedly smaller than one for H2{\mathrm{H}}_{2}H2​O, N2{\mathrm{N}}_{2}N2​, A, and He. CO has actually a greater quenching efficiency than H2{\mathrm{H}}_{2}H2​. The radius of the excited mercury atom is calculated using an improved value for the amount of resonance-radiation re-absorbed in the resonance vessel and found to be rHg\ensuremath′=2.91\ifmmode×\else\texttimes\fi10\ensuremath−8{r}_{{\mathrm{Hg}}^{\ensuremath{'}}}=2.91\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}rHg\ensuremath′​=2.91\ifmmode×\else\texttimes\fi10\ensuremath−8 cm, or 1.62 times larger than the radius of the normal atom for the case of H2{\mathrm{H}}_{2}H2​, and rHg\ensuremath′=5.5\ifmmode×\else\texttimes\fi10\ensuremath−8{r}_{{\mathrm{Hg}}^{\ensuremath{'}}}=5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}rHg\ensuremath′​=5.5\ifmmode×\else\texttimes\fi10\ensuremath−8 cm or three-fold normal for the case of CO. The apparent higher quenching efficiency of oxygen than hydrogen is explained by the partial oxidation of the mercury vapor and consequent decrease of the density of the last. It is shown that the life of metastable atoms increases with the admission of certain foreign gases into the fluorescence vessel.
A complete and general study of the dependence of life and concentration of metastable mercury atoms, optically excited, on experimental conditions, on foreign gas-pressures, and on intensity of illumination is given. This study explains why the life can not be larger than ${10}^{\ensuremath{-}2}$ second under laboratory conditions and why foreign gases act so differently in regard to the accumulation of excited atoms. The theoretical results are in good agreement with all experimental data available. An improved and more general formula for the quenching of mercury resonance radiation is obtained. The efficiencies of collisions of the second kind of metastable mercury atoms with N2{\mathrm{N}}_{2}N2​, A, and He molecules are calculated numerically. It is shown that the concentration of metastable atoms increases only with the square root of the intensity of the exciting light and not with the exciting light itself as generally assumed.
When a mercury atom in the resonance 63P16^{3}P_{1}63P1​ state collides with a nitrogen molecule, it may be transferred to the metastable 63P06^{3}P_{0}63P0​ state. The cross section for this reaction has been measured by a new method. Mercury vapor, in the presence of a known pressure of nitrogen gas, is excited by 2537A radiation. After the source of the excitation is cut off, the decay time of the imprisoned radiation is observed. The quenching collision cross section ${\ensuremath{\sigma}}_{Q}$ is calculated from the measured decay time and the known value of the imprisonment time in the absence of the quenching gas. Measurements have been taken over the temperature range 325-525\ifmmode^\circ\else\textdegree\fi{}K; ${\ensuremath{\sigma}}_{Q}$ is found to increase from 5.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}17}$ cm2{\mathrm{cm}}^{2}cm2 at the lower temperature to 1.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2 at the upper temperature.
The quenching and depolarization of mercury resonance radiation (2537 Å), induced in collisions of Hg(63P1) atoms with various molecules has been investigated using the method of delayed coincidences. The following total quenching cross sections have been obtained for the process Hg(63P1) → Hg(63P0, 61S0): Hg–H2, 24.6 Å2; Hg–D2, 22.7 Å2; Hg–CO, 21.7 Å2; Hg–CO2, 10.2 Å2; Hg–O2, 60.5 Å2; Hg–14N2, 0.73 Å2; Hg–15N2, 0.78 Å2; and Hg–Xe, < 0.002 Å2. A cross section of 267 Å2 has been measured for the depolarization of the resonance radiation by collisions with CO2 molecules.
Effect of nitrogen and of mixtures of nitrogen and carbon dioxide upon the fluorescence of mercury vapor. By "stepwise" optical excitation, unexcited mercury atoms are raised to the 23S12^{3}S_{1}23S1​ state. They may leave this level upon the emission of radiation by four paths---the first to the 21P12^{1}P_{1}21P1​ state, a transition of relatively low probability, and the other three to the 23P22^{3}P_{2}23P2​, 23P12^{3}P_{1}23P1​, and 23P02^{3}P_{0}23P0​ states with the emission of 5461A, 4358A and 4046A, respectively. Measurements, by totally independent methods, of the mean life of the 23S12^{3}S_{1}23S1​ state yielded values, when measured by the line 5461A, equal to approximately four times those when measured by either 4358A or 4046A. Upon the addition of foreign gas, then, the intensity ratio of 5461A to either 4358A or 4046A should decrease with increasing pressure while that of 4046A to 4358A should remain constant. However, these ratios were all found to be invariant with pressure, up to 400 mm in the case of nitrogen and up to 100 mm in the case of the nitrogen-carbon dioxide mixtures.
An investigation of the sensitized fluorescence of a mercury thallium mixture without and with the addition of argon and helium gases is discussed. Data taken without the addition of foreign gases are used to extend the theory of Frish and Karaulinya to a mercury thallium mixture. Relative collision cross sections for the excitation of the thallium energy states, 92S129^{2}S_{\frac{1}{2}}92S21​​, 72D52,327^{2}D_{\frac{5}{2},\frac{3}{2}}72D25​,23​​, 82S128^{2}S_{\frac{1}{2}}82S21​​, 62D526^{2}D_{\frac{5}{2}}62D25​​, and 62D326^{2}D_{\frac{3}{2}}62D23​​ were calculated for mercury thallium collisions. Data taken with the addition of argon and helium gases are given to indicate the variation of the intensity of the thallium lines as a function of argon and helium gas pressures at one constant thallium and three mercury temperatures. The explanation of the results depends on the role of mercury 63P16^{3}P_{1}63P1​ excited atoms, metastable atoms, and mercury molecules in collision with thallium atoms for energy exchange, and also requires the use of Winans' partial selection rule and other generally accepted ideas concerning energy transfer, emission, and absorption.