The Infrared Absorption Spectrum and the Molecular Structure of Ozone

Abstract

Of the seven known infrared absorption bands of ozone, four (4.7μ, 7.39μ, 9.6μ, and 11.38μ) have been investigated for the first time with a grating spectrometer. The band at 4.7μ shows three branches, not very sharply defined, while the one at 7.39μ shows only a single peak. The strongest band, at 9.6μ, has been resolved into two main branches which probably belong to two different vibrations. The band at 11.38μ has been tentatively ascribed to nitrogen pentoxide, which often occurs as an impurity in ozone. Three fundamental vibrational frequencies, viz., 528 ${\mathrm{cm}}^{-1\mathrm{}}$, 1033 ${\mathrm{cm}}^{-1\mathrm{}}$, and 1355 ${\mathrm{cm}}^{-1\mathrm{}}$, have been selected from the observational data. The rotational fine structure could not be completely resolved; it appears to have the irregularity characteristic of an asymmetrical rotator. The envelopes of the four observed bands have been completely mapped out. The infrared absorption spectrum of ozone is discussed and it is shown that the molecule cannot have the form of a straight line nor an equilateral triangle but it is probably represented by an isosceles triangle where the angle at the apex is less than 60°. By making use of these assumptions it was possible to order the observed frequencies in a fashion consistent with their envelopes. This general shape of isosceles triangle is the only one allowed by the observational data; the other shape of isosceles triangle, with apex angle greater than 60°, is ruled out.