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Physical Review

The Quenching of Mercury Resonance Radiation (2537A) by Nitrogen

C. G. Matland

Published Nov 1, 1953• 32 citations
Publisher

Abstract

When a mercury atom in the resonance $6^{3}P_{1}$ state collides with a nitrogen molecule, it may be transferred to the metastable $6^{3}P_{0}$ 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{}${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at the lower temperature to 1.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at the upper temperature.

DOI
10.1103/physrev.92.637

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6P13−6P03 Excitation Transfer in Mercury, Induced in Collisions with N2 Molecules

John M. Pitre, K. Hammond, L. Krause

The cross section for the transition $6^{3}P_{0}\ensuremath{\rightarrow}6^{3}P_{1}$ in mercury, induced in collisions with ${\mathrm{N}}_{2}$ molecules, has been determined by the method of delayed coincidences. The Hg $^{3}P_{1}$ state was excited by pulses of 2537-\AA{} Hg resonance radiation and the decay of the long-lived 2537-\AA{} afterglow was studied in relation to ${\mathrm{N}}_{2}$ pressure. The resulting cross section ${Q}_{12}(^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1})=4.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{\AA{}}}^{2}$ was found to be good agreement with the prediction of the principle of detailed balancing when compared with the cross section ${Q}_{21}(^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0})$. It was also found that, within the sensitivity of the method, collisions with ${\mathrm{N}}_{2}$ molecules do not quench $^{3}P_{1}$ or $^{3}P_{0}$ Hg atoms to the ground state.

Physical Review A•Dec 1, 1972•39 citations

Measurement of the Life of the Metastable Mercury Atom

M. L. Pool

Half value time for the ${2}^{3}$${\mathrm{P}}_{0}$ state of Hg for various pressures of admixed ${\mathrm{N}}_{2}$--- A high speed rotating disk has been used to interrupt the total radiation from a water-cooled and magnetically controlled quartz mercury arc before optically exciting mercury vapor in a quartz resonance tube at room temperature. In the neighborhood of ${10}^{\ensuremath{-}4}$ sec. after the optical excitation a flash of visible radiation from another water-cooled and magnetically controlled mercury arc was passed through the resonance tube and the absorption spectrum photographed. The line 4047 ($2^{3}P_{0}\ensuremath{-}2^{3}S_{1}$) showed strong absorption when a few millimeters of nitrogen were introduced into the resonance tube. The lines 4077, 4358, 5461, 5770 and 5790 showed no measurable absorption under similar conditions. The rate of decay of the amount of 4047 absorbed with respect to the time-wait after excitation of the mercury vapor was taken as the rate of decay of the metastable $2^{3}P_{0}$ state. The life or half-value time of the state was found to vary markedly with the pressure of admixed nitrogen. The maximum life 4.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ sec. occurred for 6.8 mm of nitrogen. No absorption of 4047 was observed upon the introduction of hydrogen, argon, neon, or helium into the resonance tube.

Physical Review•Jan 1, 1929•14 citations

The Metastable 2 p 3 -State of Mercury Atoms

S. Loria

Let us consider a mixture of mercury vapor, thallium vapor and nitrogen in a closed quartz tube under well defined conditions of pressure and temperature, illuminated by λ 2537A of constant intensity. \n \nDue to the absorption of the illuminating radiation a constant number N of mercury atoms will be activated in unit time. Those activated atoms persist in the 2p2-state for a finite time t which is known to be of the order of magnitude of 10^-7 sec [1]. If they escape collision during this period they return to their normal state in the ordinary wave-emitting radiation (resonance). They may, however, while activated, collide with nitrogen molecules, normal mercury atoms or normal thallium atoms. We shall assume, for the present, that the amount of nitrogen and thallium sufficiently exceeds the amount of mercury, so that we may disregard totally the collisions between activated and normal mercury atoms. \n \nWe assume furthermore that all collisions between activated mercury atoms and thallium atoms result in the activation of the latter, producing the fluorescence radiation of thallium with a constant energy distribution between its different lines.

Proceedings of the National Academy of Sciences•Nov 1, 1925•3 citations

Experimental Determination of the De-excitation Cross Section for the 6P13 State of Mercury by Thallium

B. C. Hudson, B. Curnutte

The de-excitation or quenching cross section of thallium for the $6^{3}P_{1}$ state of mercury has been obtained over a range of temperatures of 800 to 900\ifmmode^\circ\else\textdegree\fi{}C. Comparison of the resonance fluorescence from a mercury-thallium vapor mixture with the resonance fluorescence from a pure mercury vapor at the same number density, as determined by line absorption, allows the calculation of the de-excitation cross section. The present data together with Garrett's value of the lifetime of the $6^{3}P_{1}$ state of mercury and existing data on the vapor pressures of mercury and thallium were used to obtain values of the de-excitation cross section. Values of the cross section range from 108\ifmmode\pm\else\textpm\fi{}41 ${\mathrm{\AA{}}}^{2}$ at 800\ifmmode^\circ\else\textdegree\fi{}C to 80\ifmmode\pm\else\textpm\fi{}19 ${\mathrm{\AA{}}}^{2}$ at 900\ifmmode^\circ\else\textdegree\fi{}C. The corresponding quenching-rate coefficients varied from (5.1\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec at 800\ifmmode^\circ\else\textdegree\fi{}C to (4.0\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec at 900\ifmmode^\circ\else\textdegree\fi{}C.

Physical Review•Aug 5, 1966•6 citations

Isotope Effect in the Imprisonment of Resonance Radiation

Theodore D. Holstein, D. Alpert, A. O. McCoubrey

On theoretical grounds it is expected that the decay time of imprisoned resonance radiation in the vapor of a single even isotope of mercury should be some six times larger than that observed with the natural samples of mixed isotopic constitution. To investigate this effect experimentally, decay measurements were carried out with samples of ${\mathrm{Hg}}^{198}$ (3 percent ${\mathrm{Hg}}^{199}$ and 0.1 percent ${\mathrm{Hg}}^{200}$). For vapor densities $N\ensuremath{\lesssim}\frac{{10}^{14}}{\mathrm{cc}}$, the predicted effect was verified. For $N>\frac{{10}^{14}}{\mathrm{cc}}$, the observed decay time drops below that predicted theoretically for pure ${\mathrm{Hg}}^{198}$. This secondary effect is here attributed to the transfer of excitation from ${\mathrm{Hg}}^{198}$ to ${\mathrm{Hg}}^{199}$ and ${\mathrm{Hg}}^{200}$ by collisions of the second kind. Comparison of experimental data with an appropriately generalized theory permits estimation of the cross section for such collisions. The value so obtained is ${10}^{\ensuremath{-}13}$ ${\mathrm{cm}}^{2}$, some twenty times the gas-kinetic cross section, and in order-of-magnitude agreement with theoretical expectations.

Physical Review•Mar 15, 1952•55 citations

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

Enrique Gaviola

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.

Physical Review•Mar 1, 1929•11 citations
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 \ensuremathσQ{\ensuremath{\sigma}}_{Q}\ensuremathσQ​ 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; \ensuremathσQ{\ensuremath{\sigma}}_{Q}\ensuremathσQ​ is found to increase from 5.0\ifmmode\times\else\texttimes\fi{}10\ensuremath−17{10}^{\ensuremath{-}17}10\ensuremath−17 cm2{\mathrm{cm}}^{2}cm2 at the lower temperature to 1.0\ifmmode\times\else\texttimes\fi{}10\ensuremath−16{10}^{\ensuremath{-}16}10\ensuremath−16 cm2{\mathrm{cm}}^{2}cm2 at the upper temperature.
The cross section for the transition $6^{3}P_{0}\ensuremath{\rightarrow}6^{3}P_{1}$ in mercury, induced in collisions with N2{\mathrm{N}}_{2}N2​ molecules, has been determined by the method of delayed coincidences. The Hg 3P1^{3}P_{1}3P1​ state was excited by pulses of 2537-\AA{} Hg resonance radiation and the decay of the long-lived 2537-\AA{} afterglow was studied in relation to N2{\mathrm{N}}_{2}N2​ pressure. The resulting cross section ${Q}_{12}(^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1})=4.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ A˚2{\mathrm{\AA{}}}^{2}A˚2 was found to be good agreement with the prediction of the principle of detailed balancing when compared with the cross section ${Q}_{21}(^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0})$. It was also found that, within the sensitivity of the method, collisions with N2{\mathrm{N}}_{2}N2​ molecules do not quench 3P1^{3}P_{1}3P1​ or 3P0^{3}P_{0}3P0​ Hg atoms to the ground state.
Half value time for the 23{2}^{3}23P0{\mathrm{P}}_{0}P0​ state of Hg for various pressures of admixed N2{\mathrm{N}}_{2}N2​--- A high speed rotating disk has been used to interrupt the total radiation from a water-cooled and magnetically controlled quartz mercury arc before optically exciting mercury vapor in a quartz resonance tube at room temperature. In the neighborhood of ${10}^{\ensuremath{-}4}$ sec. after the optical excitation a flash of visible radiation from another water-cooled and magnetically controlled mercury arc was passed through the resonance tube and the absorption spectrum photographed. The line 4047 ($2^{3}P_{0}\ensuremath{-}2^{3}S_{1}$) showed strong absorption when a few millimeters of nitrogen were introduced into the resonance tube. The lines 4077, 4358, 5461, 5770 and 5790 showed no measurable absorption under similar conditions. The rate of decay of the amount of 4047 absorbed with respect to the time-wait after excitation of the mercury vapor was taken as the rate of decay of the metastable 23P02^{3}P_{0}23P0​ state. The life or half-value time of the state was found to vary markedly with the pressure of admixed nitrogen. The maximum life 4.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ sec. occurred for 6.8 mm of nitrogen. No absorption of 4047 was observed upon the introduction of hydrogen, argon, neon, or helium into the resonance tube.
Let us consider a mixture of mercury vapor, thallium vapor and nitrogen in a closed quartz tube under well defined conditions of pressure and temperature, illuminated by λ 2537A of constant intensity. \n \nDue to the absorption of the illuminating radiation a constant number N of mercury atoms will be activated in unit time. Those activated atoms persist in the 2p2-state for a finite time t which is known to be of the order of magnitude of 10^-7 sec [1]. If they escape collision during this period they return to their normal state in the ordinary wave-emitting radiation (resonance). They may, however, while activated, collide with nitrogen molecules, normal mercury atoms or normal thallium atoms. We shall assume, for the present, that the amount of nitrogen and thallium sufficiently exceeds the amount of mercury, so that we may disregard totally the collisions between activated and normal mercury atoms. \n \nWe assume furthermore that all collisions between activated mercury atoms and thallium atoms result in the activation of the latter, producing the fluorescence radiation of thallium with a constant energy distribution between its different lines.
The de-excitation or quenching cross section of thallium for the 63P16^{3}P_{1}63P1​ state of mercury has been obtained over a range of temperatures of 800 to 900\ifmmode^\circ\else\textdegree\fi{}C. Comparison of the resonance fluorescence from a mercury-thallium vapor mixture with the resonance fluorescence from a pure mercury vapor at the same number density, as determined by line absorption, allows the calculation of the de-excitation cross section. The present data together with Garrett's value of the lifetime of the 63P16^{3}P_{1}63P1​ state of mercury and existing data on the vapor pressures of mercury and thallium were used to obtain values of the de-excitation cross section. Values of the cross section range from 108\ifmmode\pm\else\textpm\fi{}41 A˚2{\mathrm{\AA{}}}^{2}A˚2 at 800\ifmmode^\circ\else\textdegree\fi{}C to 80\ifmmode\pm\else\textpm\fi{}19 A˚2{\mathrm{\AA{}}}^{2}A˚2 at 900\ifmmode^\circ\else\textdegree\fi{}C. The corresponding quenching-rate coefficients varied from (5.1\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cm3{\mathrm{cm}}^{3}cm3/sec at 800\ifmmode^\circ\else\textdegree\fi{}C to (4.0\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cm3{\mathrm{cm}}^{3}cm3/sec at 900\ifmmode^\circ\else\textdegree\fi{}C.
On theoretical grounds it is expected that the decay time of imprisoned resonance radiation in the vapor of a single even isotope of mercury should be some six times larger than that observed with the natural samples of mixed isotopic constitution. To investigate this effect experimentally, decay measurements were carried out with samples of Hg198{\mathrm{Hg}}^{198}Hg198 (3 percent Hg199{\mathrm{Hg}}^{199}Hg199 and 0.1 percent Hg200{\mathrm{Hg}}^{200}Hg200). For vapor densities $N\ensuremath{\lesssim}\frac{{10}^{14}}{\mathrm{cc}}$, the predicted effect was verified. For N>1014ccN>\frac{{10}^{14}}{\mathrm{cc}}N>cc1014​, the observed decay time drops below that predicted theoretically for pure Hg198{\mathrm{Hg}}^{198}Hg198. This secondary effect is here attributed to the transfer of excitation from Hg198{\mathrm{Hg}}^{198}Hg198 to Hg199{\mathrm{Hg}}^{199}Hg199 and Hg200{\mathrm{Hg}}^{200}Hg200 by collisions of the second kind. Comparison of experimental data with an appropriately generalized theory permits estimation of the cross section for such collisions. The value so obtained is ${10}^{\ensuremath{-}13}$ cm2{\mathrm{cm}}^{2}cm2, some twenty times the gas-kinetic cross section, and in order-of-magnitude agreement with theoretical expectations.
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 ${r}_{{\mathrm{Hg}}^{\ensuremath{'}}}=2.91\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ cm, or 1.62 times larger than the radius of the normal atom for the case of H2{\mathrm{H}}_{2}H2​, 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.