Oliver R. Wulf

The Absorption Coefficient of Nitrogen Pentoxide in the Ultraviolet and the Visible Absorption Spectrum of NO3

Absorption spectrograms have been made of the gaseous system N2O5–O3 during the decomposition of the ozone and into the subsequent decomposition of the N2O5, placing these in time such that one was taken when the system consisted essentially of only N2O5 and oxygen. From such spectrograms as the last mentioned, the absorption coefficient, α10, of N2O5 has been measured over the wave‐length range 3800–2850A. The value rises steadily from approximately 0.002 at the first wave‐length to approximately 0.52 at 2850A. The absorption coefficient curve continues to rise to shorter wave‐lengths and qualitative observations indicated no maximum as far as 2400A. No absorption which could be attributed to N2O5 could be observed in the 4500A region. Absorption spectrograms of NO3 in the visible are given. In a study using low dispersion of the influence of oxygen on the absorption spectrum of NO2, no noticeable effect was observed.

Ultraviolet Absorption of Mixtures of NO, NO2 and H2O

In considerable amounts of NO containing small amounts of NO2 a continuous absorption occurs in the ultraviolet, obscuring both the absorption of NO and that portion of the absorption of NO2 which lies below 2500A. The behavior of this absorption with respect to temperature and the partial pressures of the constituents is rather convincing evidence that it is due to N2O3. When very small amounts of water are also present a group of bands occurs in the near ultraviolet, lying in the same region but not resembling the longer wave‐length NO2 absorption. These bands appear diffuse under low dispersion but possess an ordered arrangement. With increase of temperature the intensity of the bands decreases rapidly. They begin in the vicinity of 3850A, extending to shorter wavelengths. The first members are broader and more diffuse than those that follow, indicating a predissociation process in the carrier, which is probably HONO.

Combination Frequencies Associated with the First and Second Overtone and Fundamental OH Absorption in Phenol and Its Halogen Derivatives

Absorption maxima occurring in the near infra‐red spectra of phenol and seven of its halogen derivatives have been measured and interpreted as combination frequencies in which the valence vibration of the OH group combines with frequencies of the body of the molecule. Certain of these absorptions underlie some of the trans‐peaks of the orthohalogen phenols causing such a trans‐peak to appear of larger area than that due to the trans‐peak alone. A group of the combination frequencies which lie in the range 1000–1600 cm—1 above the first overtone OH absorption have been observed as a group of an order of magnitude weaker intensity in the frequency range twice the values above the first overtone OH and also above the fundamental OH absorption, apparently involving two units of vibration in the combining frequencies. A close correspondence is found between the frequencies involved in these combination tones and the frequencies which have been observed in some of these compounds in the deep infra‐red and in Raman spectra.

The Infra‐Red Absorption of Phenol and Its Halogen Derivatives in the Region of the Second Overtone of the OH Absorption

Orthohalogen and symmetrically trihalogen substituted phenols in the region of the second overtone of the OH absorption show behavior that is similar to that in the region of the first overtone but with increased displacement of the component absorptions. Subsidiary peaks are observed in the region of the second overtone and appear to stand in ordered relation to the principal peaks. In the present work the ortho‐ and symmetrically trichloro‐, bromo‐, and iodophenols as well as pentachlorophenol and phenol itself have been studied in carbon tetrachloride solution. The tendency of phenol to associate in a series of polymers has been studied by means of the phenol absorption. Relative to phenol the association of the above‐mentioned substituted phenols is small.

A Partial Analysis of Some Infra‐Red Absorption Spectra of Organic Molecules in Dilute Solution

An attempt is made to resolve into component parts a number of relatively complex infra‐red absorption coefficient curves for several OH‐containing organic molecules in the region of the first overtone absorption of the OH group. Such analyses suggest certain relations between the structure of the molecule and its effect upon the character of the absorption of the absorbing group.

The absorption of light in the atmosphere and its relation to atmospheric ozone

In the high atmosphere the absorption of solar radiation leads to fluorescence and to persistent ionization and molecular dissociation. The absorption is almost entirely in the far ultra-violet. The degree of ionization and dissociation decreases and the degree of molecule formation increases in passing to lower altitudes, since these in general depend oppositely on collisions. At lower altitudes collisions permit frequent recombination and also the formation of new molecules which introduce new absorption. This absorption by the new molecule may in general lead to its decomposition thus setting up a photochemical steady state—the outstanding example in the atmosphere is that of ozone. Ionization will be confined chiefly to high altitudes and new molecule formation to low altitudes, not so much because of the altitudes at which the respective absorptions occur but rather because of the difference in atmospheric density. Intense absorption by oxygen in the intermediate altitudes leads to inconsiderable amounts of ozone. Moreover, the amount of new molecule formed in a photochemical steady state depends not so much upon the intensity of the absorption of the producing wave-lengths but upon the ratio of the intensities of the producing and decomposing wave-lengths. In a gas distributed exponentially with height, as in a gravitational field, the form of the curve, absorption versus height, is the same for all values of the absorption-coefficient; the curve is simply transposed in height. Thus it comes about that in the production of ozone, not the strongly absorbed radiation which is absorbed at great altitudes, but the very weakly absorbed radiation, which penetrates deeply, is the important radiation in its production. It has been somewhat lost sight of that active wavelengths, extremely weakly absorbed by oxygen but carrying as much or indeed greater total energy, are absorbed just as completely but at low altitudes as those possessing high absorption-coefficients which are absorbed at high altitudes. In this connection the pressure-dependent absorption in oxygen is also important.