The Einstein coefficient A of the metastable level A3∑ of the nitrogen molecule is measured in a de discharge by the concurrent determination of the number per second of quanta of the Vegard-Kaplan band emitted and the concentration of the metastable excited level. This concentration is derived from the strength of the absorption spectrum of the metastable level which consists of the first positive bands. The result is a half-life of about 0.9 second.

We obtain numerically computed solutions to the Boltzmann equation giving the electron energy distribution in weakly ionized air under the following assumptions: (1) that there are present a static magnetic field and an electric field of constant direction (perpendicular to the magnetic field) and a constant rms value; (2) that the gas is homogeneous and the fields uniform in space; (3) that the degree of ionization is weak enough so that electron-electron and electron-ion collisions are negligible; (4) that the fields are such that the average electron energy is much larger than the thermal energy of the gas molecules, and that the heating of the gas by the electrons is negligible; (5) that processes of creation and removal of free electrons are negligible; and (6) that electrons may lose energy in elastic collisions and may also excite rotational, vibrational, and electronic degrees of freedom. To describe these energy-loss processes we use experimental cross sections. We take the constituents of the air to be ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, and O, the later being included for upper atmosphere applications. We give distribution functions for a number of limiting cases and compare our solutions to others which may be obtained by less extensive calculations. We demonstrate that while the ratio of electric field to pressure is a good scaling factor for dc excitation this is not the case if either the excitation frequency or the gyro frequency is large compared to the collision frequency.

To measure small concentrations of molecules, particularly in a metastable state, we have developed a form of double-beam absorption spectrometer. This instrument allows one to use as an absorber a tube in which a dc discharge creates unstable species. The design provides that light emitted from this discharge shall not interfere with the absorption measurement. We use as a background source a second discharge tube emitting the band system whose absorption we wish to observe. We measure the absorption of a single vibrational band of known probability of transition. A detailed analysis of the relative intensities of all the lines constituting the band is then necessary in order to extract the population of the metastable level.