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Canadian Journal of Research

DURATION OF META-STABLE STATES, NEON

John M. Anderson

Published Oct 1, 1932• 3 citations
Publisher

Abstract

The rate of decay of absorption of six neon lines λ 6402, λ 6334, λ 6266, λ 6163, λ 6143 and λ 5945 has been measured for a series of pressures at room temperature and at the temperature of liquid air. Curves showing the variation of half-life with pressure have been plotted for each line at both temperatures. It is found that the function [Formula: see text] is exponential in the time, and that the rate of decay is markedly different at the same pressure and temperature for different lines ending in the same meta-stable state.

DOI
10.1139/cjr32-093

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The mean life of the mercury line $\ensuremath{\lambda}2537$ was measured by the alternating voltage method previously described by Webb. The radiation was excited in a quartz tube by impact with electrons from a hot cathode. The photoelectric system was contained in a separate tube also of quartz. The photoelectric surface was zinc evaporated on a nickel plate. Measurements of the apparent life were made with diminishing mercury vapor pressures until further reduction of pressure produced no change in the measured rate of decay of the radiation. At these low pressures (below 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ mm, for the geometry used) the absorption and reemission of the radiation was negligible and the true life of a single excitation process was measured. This was found to be 1.08\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec. with an estimated precision of one percent.Absorption coefficient of $\ensuremath{\lambda}1849$. An absorption cell with a one mm thick absorbing layer of mercury vapor was mounted so as to move in and out between the excitation and photoelectric tubes used in the above measurements. The absorption of $\ensuremath{\lambda}1849$ was measured at pressures such that the absorption of $\ensuremath{\lambda}2537$ was negligible. From this the atomic absorption coefficient for the main component of the line was found to be 6.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ from which the mean life of the $2^{1}P_{1}$ state was calculated to be 2.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. with an estimated precision of 25 percent.

Physical Review•Jun 1, 1932•17 citations
The rate of decay of absorption of six neon lines λ 6402, λ 6334, λ 6266, λ 6163, λ 6143 and λ 5945 has been measured for a series of pressures at room temperature and at the temperature of liquid air. Curves showing the variation of half-life with pressure have been plotted for each line at both temperatures. It is found that the function [Formula: see text] is exponential in the time, and that the rate of decay is markedly different at the same pressure and temperature for different lines ending in the same meta-stable state.
Improved apparatus has been designed to determine the rate of decay after excitation of the populations of the four states in the 1s22s22p53s configuration of neon. An absorption method is employed. Measurements show that the population of the 3P2 state decays exponentially. The decay curves for the 3P1 and 3P0 states may be expressed as the sum of two exponential rates of decay. Atoms in the 1P1 state disappear very rapidly making measurements difficult; the decay is assumed to be exponential. Curves of mean life as obtained from these exponentials are plotted against pressure for all four states. The initial populations of the four states, determined from initial absorption, are of the order of 109 atoms per cc. and are plotted as a function of pressure. Within the limits of error the populations so calculated are the same for different absorption lines.
The half-value time of absorption from meta-stable electronic atomic states is calculated on the hypothesis that the whole decay is due to collision phenomena. Definite assumptions, which include the atomic energy level scheme, are made as to the efficiency of collisions and the interaction of two meta-stable states in these processes. The assumption adopted as the only one producing an approximation to experimental facts shows that the probability of an exchange is dependent on the absolute value of the energy difference between the states concerned. The results calculated from the final formula, for helium, neon and argon at normal and very low temperatures depend on one arbitrary constant, which is the same for all states and gases considered, and show fair agreement with any experimental values so far published. An estimate is made of the energy tolerance of a quantum transition.
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.
The current and pressure dependence of the decay of the 3P0^{3}P_{0}3P0​ metastable level of neon was measured by using a light absorption method. The decay was found to be nonexponential and current dependent at normal excitation currents. At extremely low excitation current, however, the 3P0^{3}P_{0}3P0​ decay becomes exponential and current independent. The mean lives associated with such exponential decays were measured as a function of pressure. The results are in agreement with the usual theoretical relation based on metastable destruction by diffusion to the container walls at low pressure and two-body collisions at high pressures. The pressure dependence of the 3P2^{3}P_{2}3P2​ level was also studied. It was found, as previously reported by Grant, that the experimental results for the pressure range from 2 to 20 mm of mercury, where diffusion loss is small, do not agree with the usual theoretical prediction.
The mean life of the mercury line $\ensuremath{\lambda}2537$ was measured by the alternating voltage method previously described by Webb. The radiation was excited in a quartz tube by impact with electrons from a hot cathode. The photoelectric system was contained in a separate tube also of quartz. The photoelectric surface was zinc evaporated on a nickel plate. Measurements of the apparent life were made with diminishing mercury vapor pressures until further reduction of pressure produced no change in the measured rate of decay of the radiation. At these low pressures (below 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ mm, for the geometry used) the absorption and reemission of the radiation was negligible and the true life of a single excitation process was measured. This was found to be 1.08\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec. with an estimated precision of one percent.Absorption coefficient of $\ensuremath{\lambda}1849$. An absorption cell with a one mm thick absorbing layer of mercury vapor was mounted so as to move in and out between the excitation and photoelectric tubes used in the above measurements. The absorption of $\ensuremath{\lambda}1849$ was measured at pressures such that the absorption of $\ensuremath{\lambda}2537$ was negligible. From this the atomic absorption coefficient for the main component of the line was found to be 6.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ from which the mean life of the 21P12^{1}P_{1}21P1​ state was calculated to be 2.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. with an estimated precision of 25 percent.