FROM CURRENT LITERATURE

ARTIFICIAL FLASH IN THE UPPER LAYERS OF THE ATMOSPHERE

The journal Scientific American (vol. 194, No. 5, May 1956, p. 56) reports on an interesting experiment carried out on the night of March 14, 1956, in New Mexico.

With the aid of a rocket, 10 kg of nitric oxide NO was delivered to an altitude of about 100 km.

When the nitric oxide was released into the atmosphere at this altitude, a glow arose, four times brighter than the glow of Venus. Gradually the luminous region reached an apparent size several times greater than the disk of the Moon, corresponding to a luminous sphere 3–4 km in diameter with a brightness half that of the Moon. After several hours, toward morning, the glow, gradually spreading out, disappeared.

The explanation of the phenomenon is that NO serves as a catalyst by means of which the reaction of recombination of oxygen atoms occurs, with a considerable part of the recombination energy being released in the form of visible light.

Under the action of the ultraviolet part of the solar spectrum in the upper layers of the atmosphere, dissociation of molecular oxygen takes place,

\[ \mathrm{O}_2 + h\nu = \mathrm{O} + \mathrm{O}^{*}. \]

The excited oxygen atom \(\mathrm{O}^{*}\) immediately emits light or gives up its excitation energy in collisions with any molecules. Therefore the process of recombination with emission of light, the reverse of the photodissociation process described above, proves impossible. In the normal state, oxygen atoms combine into a molecule with emission of light only with a very small probability.

Recombination of oxygen atoms could also occur in triple collisions,

\[ \mathrm{O} + \mathrm{O} + \mathrm{M} = \mathrm{O}_2 + \mathrm{M}, \]

in which the third particle (\(\mathrm{M}\), of any chemical composition) would carry away the recombination energy. However, at the negligible density

at an altitude of 100 km such a process proceeds very slowly. As a result, in the ionosphere, not only by day, during irradiation by the Sun, but also at night, a high concentration of atomic oxygen is maintained.

In the presence of nitric oxide, the following sequence of reactions takes place:

\[ (1)\quad \mathrm{NO}+\mathrm{O}=\mathrm{NO}_2+h\nu, \]

\[ (2)\quad \mathrm{NO}_2+\mathrm{O}=\mathrm{NO}+\mathrm{O}_2+50\ \text{kcal/mole}. \]

The first process is the reverse of the well-known reaction of photodissociation of nitrogen dioxide. The second process restores nitric oxide. On the whole, nitric oxide is not consumed and plays the role of a catalyst. The process does not require triple collisions and proceeds through two successive double collisions. About half of the recombination energy is released in the form of light.

The note observes that, in principle, the recombination energy could be used by a rocket, so that a rocket moving at this altitude without fuel would not violate the principles of thermodynamics. The chief practical difficulty is connected with the negligible density of the air at the altitude where nonequilibrium concentrations of oxygen atoms are present.

The experiment was carried out by a group under the direction of M. Zelikov. It may be hoped that a detailed scientific report on the experiment will appear soon.

Ya. B. Zel’dovich