Spectroscopic Evidence of two Types of Ammonia Molecule

A two-fold difference exists in the equations expressing the anharmonic frequencies arising from vibratory energy changes in ammonia molecules in solution and in gaseous form. The greater coefficient of the $n^2$ term in the former case, indicating a more rapid approach of the energy terms toward confluence, is assumed to arise from the proximity of the molecules of the solvent. The presence of a constant term of appreciable magnitude in the solution equation is interpreted as measuring the energy required to change the molecule from an $\alpha$ form to a $\beta$ form of greater potential energy. Chemical support for this latter interpretation is sought in some earlier measurements by Baly and Duncan on the difference in the decomposition rates of ammonia both after immediate evaporation from the liquid and after it had stood for a considerable length of time.

It becomes easier to interpret the Raman spectrum of liquid ammonia, ammonia in aqueous solution and a liquid organic derivative of ammonia, aniline, when the existence of a constant in the infra-red formula is recognized.