The measurement of the absorption of a parallel light beam from a resonance lamp by an absorption tube filled with mercury vapor leads to the determination ot the lifetime of the 6/sup 3/P/sub 1/ excited state of mercury. The same value ( lambda = 1.16 x 10/sup -7/ sec) was found for all the isoiopes of mercury. (tr-auth)
LIFETIME OF THE 6sup3Psub1 EXCITED STATE OF MERCURY VAPOR FOR THE ISOTOPES WITH EVEN AND ODD MASSES
The de-excitation or quenching cross section of thallium for the 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 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 at 800\ifmmode^\circ\else\textdegree\fi{}C to 80\ifmmode\pm\else\textpm\fi{}19 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/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/sec at 900\ifmmode^\circ\else\textdegree\fi{}C.
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 21P1 state was calculated to be 2.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. with an estimated precision of 25 percent.
Half value time for the 23P0 state of Hg for various pressures of admixed 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 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 absorption of the resonance radiation (2536A) of mercury was studied by dividing the radiation from a resonance lamp into two parts, each part going into a separate photo-electric cell. An absorption cell containing mercury vapor whose pressure could be controlled by cooling a side tube was placed in the path of one beam. The ratio of the amount of light passing into each beam could be varied by a mechanical device. From the setting of the mechanical device, giving a balance between the two photo-electric currents, the absorption of the mercury vapor could be inferred. The absorption per atom was calculated and found to decrease rapidly as the total amount of absorbing vapor was increased, thus showing that the resonance radiation is not homogeneous. The maximum atomic absorption coefficient was 11\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$, which indicates that an atom can stop the radiation which falls upon an area one hundred times larger than its cross sectional area.
Abstract It is known that the fluorescence of mercury vapour can be excited by absorption in the region λ 1850, situated near the resonance line 1 1S0- 1 1P1, and in the region of band absorption λ 2345. It can also be excited by absorption in the region of the resonance line 1 1S0— 2 3P1 2536.52. In this latter case it has, I believe, been generally supposed that fluorescence is not obtained unless excitation is fairly close to the resonance line. Thus Prings-heim and Terenin found that a hot mercury lamp (punktlampe of Heraeus) or an overloaded ordinary 220-volt mercury lamp does not give band fluorescence of any kind. In the hot lamp the core of the resonance line is removed by self reversal. It is, however, well known that unexcited mercury vapour has an absorption band beginning near the resonance line 2537, and extending, if the vapour is dense, to a distance of some hundreds of Ångstroms towards longer waves. The question arises whether this absorption is accompanied by fluorescent emission or not.
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.