The Isotope Effect on Band Spectrum Intensities

Theory of the isotope effect on intensities.---It is shown that there is no change in the electronic part of the transition probability with nuclear mass, and that the vibrational part is the only part that does show an effect. This effect is calculated on the basis of Hutchisson's expressions for the vibrational transition probability. The effect of a change in nuclear mass on the population of the initial state is also found if this population is given by the simple Boltzmann distribution.Application of the theory to specific cases.---The magnitude of the isotope effect is found for certain bands of O₂, NO, and Cl₂ which have been used recently to measure the abundance of the isotopes of these substances by means of their band spectrum. The effect is small, being ordinarily less than ten percent, but it can not generally be neglected.