Pressure broadening in the gamma-bands of nitric oxide
The pressure broadening in the [gamma]-bands of nitric oxide, which has been the subject of considerable controversy in the literature, has been studied quantitatively with the Cary Ultraviolet Spectrophotometer. The behavior of the optical density, as a function of total pressure and of the amount...
| Summary: | The pressure broadening in the [gamma]-bands of nitric oxide, which has been the subject of considerable controversy in the literature, has been studied quantitatively with the Cary Ultraviolet Spectrophotometer. The behavior of the optical density, as a function of total pressure and of the amount of gas in the path, has been investigated for the [gamma](1,0) and [gamma](0,0) bands. Both the nitric oxide self-broadening and the broadening by nitrogen were studied. The classical theory of Lorentz gives an adequate description of the effect. Curves of growth computed from a model of the spectrum near the band head of [gamma](0,0) have been used to analyze the pressure effect quantitatively. Without recourse to absolute intensity data it is not possible to do more than show that the collision diameter is less than 9 A. The recent measurements of intensity made by Weber and Penner permit the collision diameter to be estimated as 3.8 A. By this criterion the pressure broadening cannot be called "abnormal."
The photographic work of Naude on the pressure effect has given support to the suggestion of a large pressure broadening. A photograph taken by him shows no fine structure at a pressure of 450 mm Hg, and this was attributed to a broadening of the lines into one another. A photograph taken in this laboratory under the same conditions is in strong disagreement with his results, showing very clear fine structure. There exists at present no other evidence on pressure broadening in the [gamma]-bands which cannot be harmonized with the interpretation given above. It may be concluded that there is no evidence from the pressure broadening effect for a pressure-induced predissociation in these bands of nitric oxide.
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