XLVII. The halogen hydrides

Summary THE absorption-band spectra in the infra-red of the halogen hydrides HF, HCl, HBr have recently been determined very carefully by several investigators. In this paper the experimental data have been analysed with the aid of the energy-formula developed by Born and Hückel. It is shown that the values of the coefficients in the formula l/λ=c 0+c 1 m+c 2 m 2+c 3 m 3 which embodies the experimental results for the main band and its overtones are, within the limits of experimental error, consistent with theory. The accuracy is not sufficient, however, to decide whether the “zero-point energy” exists or not. The significance of the constants in the formula is discussed. Their determination makes it possible to evaluate the variation with distance of the force acting on the hydrogen nucleus as it vibrates along the line joining the two nuclei. The range of vibration for one, two, and three energy quanta is calculated.