The experiments of Wood and of Gaviola show that when mercury vapor is illuminated by light from a mercury arc, and nitrogen is added in increasing amounts, the concentration of atoms in the $^{3}P_{2}$ state passes through a minimum. No simple theory accounts for this result. An explanation involving excitation of atoms in the $^{3}P_{1}$ state by vibrating nitrogen molecules is discussed. The results obtained when a filter of bromine vapor is used indicate a transfer of excited mercury atoms from one to another $^{3}D$ state upon collision with nitrogen.
The experiments of Wood and of Gaviola show that when mercury vapor is illuminated by light from a mercury arc, and nitrogen is added in increasing amounts, the concentration of atoms in the 3P2 state passes through a minimum. No simple theory accounts for this result. An explanation involving excitation of atoms in the 3P1 state by vibrating nitrogen molecules is discussed. The results obtained when a filter of bromine vapor is used indicate a transfer of excited mercury atoms from one to another 3D state upon collision with nitrogen.
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 23S1 state. They may leave this level upon the emission of radiation by four paths---the first to the 21P1 state, a transition of relatively low probability, and the other three to the 23P2, 23P1, and 23P0 states with the emission of 5461A, 4358A and 4046A, respectively. Measurements, by totally independent methods, of the mean life of the 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.
A mixture of potassium vapor and mercury vapor contained in a tube fashioned after the Cario-Lochte-Holtgreven sodium vapor lamp was radiated by light from a water-cooled mercury arc. The resulting fluorescence radiation contained potassium lines as well as two of the three known K2 absorption bands and a new band with maximum at 5721A. On exposure of the mixture to light from a hot mercury arc or to light having all wave-lengths shorter than 2800A filtered out, the fluorescence was eliminated. This indicated that the excitation was caused by absorption of 2536A by the mercury. Absorption of the 2536A mercury line raises the mercury atom to the 63P1 state, having an energy of 4.86 volts. The ionization potential of potassium is 4.32 volts; thus in a collision of the second kind, the excited mercury atom has enough energy to ionize the potassium atom. There was no evidence of a potassium emission from an energy state in the continuum equal in energy to the Hg 63P1 or 63P0 states. There were, however, two strong lines in fluorescence which could not be ascribed to the usual K energy levels nor to any probable impurity. To test whether or not ionization of potassium actually takes place, a filament was introduced into the tube to supply electrons. A large increase in intensity of the fluorescence of potassium lines was obtained with the hot filament. It was furthermore found that the intensity increased with filament temperature.
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.
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, 92S21, 72D25,23, 82S21, 62D25, and 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 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.
Abstract As I have shown in numerous publications, the vapour of mercury in vacuo, even at temperatures below the solidifying point of the metal, when illuminated by the light of a water-cooled quartz mercury lamp, emits the monochromatic radiation of wave-length 2536. According to Bohr’s theory, this resonance radiation results from the fall of an electron from the 2p2 orbit, to which it has been raised from the IS orbit by the absorption of one quantum of 2536 radiation, back to the IS orbit, the orbit occupied by the electron when the atom is in its normal state. An atom in which the electron has been brought to the 2p2 orbit is in a condition to absorb the radiation of any other line produced by the fall of electrons from outer orbits to orbit 2p2, and Fuchtbauer has shown, in an extremely interesting and important paper (‘Physik. Zeit.,’ 1920), that a large number of the arc lines of mercury are radiated by cold mercury vapour illuminated by the mercury arc. He showed that, if the 2536 radiation was screened off by glass, none of the other lines appeared, and explained their presence as the result of the absorption by excited atoms with electrons at the 2p2 level, of the radiations terminating at this level, by which the electrons are carried out to other-orbits, from which they can fall back in various ways, giving rise to emission lines in the process. Though Fuchtbauer‘s experiment did not prove that this process actually took place, his explanation was the only one possible on modern theory, and the experiments which are to be considered in the present paper show that it was correct. Twenty years ago the most that could have been said would have been that the absorption of the 2536 radiation “shook” the atom in some way, causing it to emit its other frequencies as a sort of fluorescence, since Fuchtbauer’s experiment did not show that excitation by lines other than the 2536 line was necessary for the emission of the arc spectrum. To demonstrate experimentally that the step-by-step transfer of electrons from orbit to orbit actually takes place, it is necessary to illuminate the mercury vapour with various combinations of monochromatic light, and study the resultant emission spectrum.
The concentration of metastable atoms in presence of 3 mm nitrogen obtained using the measurements of Stuart seems to be in contradiction with a calculation given here using observations of Wood. The contradiction disappears if the different statistical weights of the levels 23P1 and 23P0 are taken in account. Corrected curves for the number of metastable atoms as functions of the foreign gas pressure are given for CO, H2O, N2, A and He which are to replace the corresponding curves of the previous paper. It is shown that the assumption of the author that by high primary light intensities the number of metastable atoms increases only with the square root of the intensity is strikingly supported by measurements of Wood.