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The Imprisonment and Quenching of Sodium and Potassium Resonance Radiation.

G. H. Copley

Published Jan 1, 1969• 0 citations
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Abstract

The met h o d of delayed coincidences for measu r i n g lifetimes of excited states has been used to investigate imprisonment of radiation in potassium vapor and to measure quenching cross sections in mixtures of potassium w ith diatomic gases and sodium wi t h noble gases.The me thod has also been u s e d to investigate the possibility that a longlived molec u l a r complex might be formed in inelastic collisions between 2 potassium and xenon, which lead to excitation transfer between the P potassium states.The alkali metal atoms were excited w i t h short pulses of resonance radiation, and the delays between the exciting and fluores cent pulses were m e a s u r e d w i t h a time-to-amplitude converter.At 10 3 pure potassium densities below 10 atoms/cm , the m e a s u r e d lifetimes approach the constant values of 27.8 + 0 .8 and 27.6 + 0 .8 nsec, 2 2 corresponding to the m e a n lifetimes of the 4 ^^2 anc* ^ ^3 / 2 s t a t e s > respectively.At higher densities, the apparent lifetimes are in satisfactory agreement w i t h the predictions of H o l s t e i n 's theory.The decrease in the apparent lifetimes, u p o n addition of diatomic gases to the potassium vapor, yielded cross sections for quenching collisions w it h N^, H^, HD and D^, which equal 34.0 + 2 .0 X2, 9.4 + 1.3 X2, 11.9 + 1.5 X2 and 8 .0 + 2 .0 X2, respectively.Addition of the noble gases He, Ne, Kr, Ar and Xe to sodium vapor did not lead to any measurable change in the decay rates for the sodium states within the iii

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Trapping and quenching of potassium resonance radiation

G. H. Copley, L. Krause

The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.

Canadian Journal of Physics•Mar 1, 1969•45 citations

Inelastic Collisions between Excited Alkali Atoms and Molecules. II. The Quenching of Sodium Resonance Radiation by N2 , H2 , HD, and D2

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The cross sections for quenching collisions between excited sodium atoms and ${\mathrm{N}}_{2}$, ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$ molecules in their electronic ground states have been determined using a delayed-coincidence method. The sodium atoms in mixtures with the gases were excited with 20-nsec pulses of NaD radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-pulse-height converter. The resulting pulse-height spectra, which were accummulated in a 400-channel kicksorter, yielded the effective lifetimes ${\ensuremath{\tau}}^{\ensuremath{'}}$ of the sodium resonance state, which are shorter than the natural lifetime $\ensuremath{\tau}$ because of the nonradiative decay induced in collisions with the molecules. The cross sections for collisions with ${\mathrm{N}}_{2}$, ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$, obtained from an analysis of the dependence of ${\ensuremath{\tau}}^{\ensuremath{'}}$ on the gas pressures, are 30.4\ifmmode\pm\else\textpm\fi{}1.2, 16.2\ifmmode\pm\else\textpm\fi{}0.3, 11.6\ifmmode\pm\else\textpm\fi{}0.4, and 9.8\ifmmode\pm\else\textpm\fi{}0.3 ${\mathrm{\AA{}}}^{2}$, respectively.

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Effect of Imprisonment of Radiation in Sodium Vapor on the Measured Lifetime of the 3 P2 States

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The effect of imprisonment of radiation in sodium vapor on the measured lifetime of the $3 ^{2}P$ states has been investigated in an experiment in which the atoms in the vapor were excited with 10-nsec pulses of resonance radiation and the elapsed times between the exciting and the fluorescent pulses were recorded using a time-to-amplitude converter and kicksorter. At vapor densities below ${10}^{10}$ atoms/${\mathrm{cm}}^{3}$, where there is no multiple scattering, the measured lifetime reaches a constant value of (1.63\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec, equal to the natural lifetime of the $3 ^{2}P$ states. In the density range ${10}^{9}$-${10}^{13}$ atoms/${\mathrm{cm}}^{3}$, the variation of the effective lifetime with the vapor density is in good agreement with the predictions of Milne's theory of radiation trapping; agreement with Holstein's theory is observed only in the range ${10}^{12}$-${10}^{13}$ atoms/${\mathrm{cm}}^{3}$. The results of a subsidiary Hanle experiment show that a multiply scattered photon of sodium resonance fluorescence loses its original polarization and that, at high sodium vapor pressure, coherence is not preserved.

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Collision-Induced Mixing in the First Excited States of Sodium and Potassium

J. A. Jordan, P. A. Franken

The cross sections for the collision-induced transfer of excitation from the $^{2}P_{\frac{3}{2}}$ level to the $^{2}P_{\frac{1}{2}}$ level of the first excited states of the alkali atoms have been measured for several alkali-noble gas systems. The cross sections were determined with a conventional resonance fluorescence technique in which the radiation from a spectral source was absorbed and re-emitted by an alkali vapor at low pressure (\ensuremath{\sim}${10}^{\ensuremath{-}6}$ Torr), and the scattered light analyzed with a scanning spectrometer. Provision was made for the introduction of various noble gases at controlled pressures into the alkali vapor. The determined cross sections are (in units of ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$): Na-He, 41.1\ifmmode\pm\else\textpm\fi{}2.9; Na-Ne, 36.1\ifmmode\pm\else\textpm\fi{}2.5; Na-Ar, 64.6\ifmmode\pm\else\textpm\fi{}5.2; Na-Kr, 68.2\ifmmode\pm\else\textpm\fi{}5.5; Na-Xe, 61.8\ifmmode\pm\else\textpm\fi{}4.9; K-He, 52.8\ifmmode\pm\else\textpm\fi{}5.8; K-Ne, 14.0\ifmmode\pm\else\textpm\fi{}1.2; K-Ar, 34.0\ifmmode\pm\else\textpm\fi{}3.1. The quoted errors are estimated 70% confidence intervals. The measurements are compared with other experimental results and with various estimated cross sections.

Physical Review•Feb 4, 1966•39 citations

SENSITIZED FLUORESCENCE IN VAPORS OF ALKALI METALS: IX. ENERGY TRANSFER IN COLLISIONS BETWEEN SODIUM AND INERT GAS ATOMS

John M. Pitre, L. Krause

The total cross sections for inelastic collisions between sodium and inert gas atoms, leading to 3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, have been determined in a series of sensitized fluorescence experiments with sodium – inert gas mixtures. The sodium vapor was maintained at a pressure of 5 × 10−7 mm Hg, at which there is no trapping of the resonance radiation, and the inert gas pressures ranged from 0 to 1 mm Hg. The cross sections Q1(3 2P1/2 → 3 2P3/2) and Q2(3 2P1/2 ← 3 2P3/2) are as follows: Na–He, 86.0 and 44.8 Å2; Na–Ne, 67.0 and 35.4 Å2; Na–Ar, 110 and 55.9 Å2; Na–Kr, 85.0 and 43.6 Å2; Na–Xe, 89.8 and 45.6 Å2. The ratios Q1/Q2 are in agreement with the value predicted from the principle of detailed balancing and the cross sections also agree, as to order of magnitude, with some theoretically predicted values.

Canadian Journal of Physics•Aug 1, 1967•69 citations
The met h o d of delayed coincidences for measu r i n g lifetimes of excited states has been used to investigate imprisonment of radiation in potassium vapor and to measure quenching cross sections in mixtures of potassium w ith diatomic gases and sodium wi t h noble gases.The me thod has also been u s e d to investigate the possibility that a longlived molec u l a r complex might be formed in inelastic collisions between 2 potassium and xenon, which lead to excitation transfer between the P potassium states.The alkali metal atoms were excited w i t h short pulses of resonance radiation, and the delays between the exciting and fluores cent pulses were m e a s u r e d w i t h a time-to-amplitude converter.At 10 3 pure potassium densities below 10 atoms/cm , the m e a s u r e d lifetimes approach the constant values of 27.8 + 0 .8 and 27.6 + 0 .8 nsec, 2 2 corresponding to the m e a n lifetimes of the 4 ^^2 anc* ^ ^3 / 2 s t a t e s > respectively.At higher densities, the apparent lifetimes are in satisfactory agreement w i t h the predictions of H o l s t e i n 's theory.The decrease in the apparent lifetimes, u p o n addition of diatomic gases to the potassium vapor, yielded cross sections for quenching collisions w it h N^, H^, HD and D^, which equal 34.0 + 2 .0 X2, 9.4 + 1.3 X2, 11.9 + 1.5 X2 and 8 .0 + 2 .0 X2, respectively.Addition of the noble gases He, Ne, Kr, Ar and Xe to sodium vapor did not lead to any measurable change in the decay rates for the sodium states within the iii
The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.
The cross sections for quenching collisions between excited sodium atoms and N2{\mathrm{N}}_{2}N2​, H2{\mathrm{H}}_{2}H2​, HD, and D2{\mathrm{D}}_{2}D2​ molecules in their electronic ground states have been determined using a delayed-coincidence method. The sodium atoms in mixtures with the gases were excited with 20-nsec pulses of NaD radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-pulse-height converter. The resulting pulse-height spectra, which were accummulated in a 400-channel kicksorter, yielded the effective lifetimes ${\ensuremath{\tau}}^{\ensuremath{'}}$ of the sodium resonance state, which are shorter than the natural lifetime $\ensuremath{\tau}$ because of the nonradiative decay induced in collisions with the molecules. The cross sections for collisions with N2{\mathrm{N}}_{2}N2​, H2{\mathrm{H}}_{2}H2​, HD, and D2{\mathrm{D}}_{2}D2​, obtained from an analysis of the dependence of ${\ensuremath{\tau}}^{\ensuremath{'}}$ on the gas pressures, are 30.4\ifmmode\pm\else\textpm\fi{}1.2, 16.2\ifmmode\pm\else\textpm\fi{}0.3, 11.6\ifmmode\pm\else\textpm\fi{}0.4, and 9.8\ifmmode\pm\else\textpm\fi{}0.3 A˚2{\mathrm{\AA{}}}^{2}A˚2, respectively.
The effect of imprisonment of radiation in sodium vapor on the measured lifetime of the 32P3 ^{2}P32P states has been investigated in an experiment in which the atoms in the vapor were excited with 10-nsec pulses of resonance radiation and the elapsed times between the exciting and the fluorescent pulses were recorded using a time-to-amplitude converter and kicksorter. At vapor densities below 1010{10}^{10}1010 atoms/cm3{\mathrm{cm}}^{3}cm3, where there is no multiple scattering, the measured lifetime reaches a constant value of (1.63\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec, equal to the natural lifetime of the 32P3 ^{2}P32P states. In the density range 109{10}^{9}109-1013{10}^{13}1013 atoms/cm3{\mathrm{cm}}^{3}cm3, the variation of the effective lifetime with the vapor density is in good agreement with the predictions of Milne's theory of radiation trapping; agreement with Holstein's theory is observed only in the range 1012{10}^{12}1012-1013{10}^{13}1013 atoms/cm3{\mathrm{cm}}^{3}cm3. The results of a subsidiary Hanle experiment show that a multiply scattered photon of sodium resonance fluorescence loses its original polarization and that, at high sodium vapor pressure, coherence is not preserved.
An upper limit of ${10}^{\ensuremath{-}2}$ A˚2{\mathrm{\AA{}}}^{2}A˚2 is obtained for the quenching cross section of sodium resonance fluorescence when the excited sodium atoms are in collision with inert-gas atoms in their ground state. Excitation of sodium vapor at a pressure of 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ Torr is followed by observation of the decay of the fluorescence using the method of delayed coincidences. The decay time of the fluorescence is unaffected by the presence of the inert gases He, Ne, A, Kr, and Xe at pressures up to 800 Torr, and at temperatures of 130 and 210\ifmmode^\circ\else\textdegree\fi{}C.
The cross sections for the collision-induced transfer of excitation from the 2P32^{2}P_{\frac{3}{2}}2P23​​ level to the 2P12^{2}P_{\frac{1}{2}}2P21​​ level of the first excited states of the alkali atoms have been measured for several alkali-noble gas systems. The cross sections were determined with a conventional resonance fluorescence technique in which the radiation from a spectral source was absorbed and re-emitted by an alkali vapor at low pressure (\ensuremath{\sim}${10}^{\ensuremath{-}6}$ Torr), and the scattered light analyzed with a scanning spectrometer. Provision was made for the introduction of various noble gases at controlled pressures into the alkali vapor. The determined cross sections are (in units of ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2): Na-He, 41.1\ifmmode\pm\else\textpm\fi{}2.9; Na-Ne, 36.1\ifmmode\pm\else\textpm\fi{}2.5; Na-Ar, 64.6\ifmmode\pm\else\textpm\fi{}5.2; Na-Kr, 68.2\ifmmode\pm\else\textpm\fi{}5.5; Na-Xe, 61.8\ifmmode\pm\else\textpm\fi{}4.9; K-He, 52.8\ifmmode\pm\else\textpm\fi{}5.8; K-Ne, 14.0\ifmmode\pm\else\textpm\fi{}1.2; K-Ar, 34.0\ifmmode\pm\else\textpm\fi{}3.1. The quoted errors are estimated 70% confidence intervals. The measurements are compared with other experimental results and with various estimated cross sections.
The total cross sections for inelastic collisions between sodium and inert gas atoms, leading to 3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, have been determined in a series of sensitized fluorescence experiments with sodium – inert gas mixtures. The sodium vapor was maintained at a pressure of 5 × 10−7 mm Hg, at which there is no trapping of the resonance radiation, and the inert gas pressures ranged from 0 to 1 mm Hg. The cross sections Q1(3 2P1/2 → 3 2P3/2) and Q2(3 2P1/2 ← 3 2P3/2) are as follows: Na–He, 86.0 and 44.8 Å2; Na–Ne, 67.0 and 35.4 Å2; Na–Ar, 110 and 55.9 Å2; Na–Kr, 85.0 and 43.6 Å2; Na–Xe, 89.8 and 45.6 Å2. The ratios Q1/Q2 are in agreement with the value predicted from the principle of detailed balancing and the cross sections also agree, as to order of magnitude, with some theoretically predicted values.