The isotope effect: Prediction, discussion, and discovery

TL;DR

This paper reviews the historical development of the isotope effect, highlighting its theoretical prediction, experimental discovery, and significance in atomic and molecular spectroscopy over the past century.

Contribution

It provides a comprehensive discussion of the isotope effect's prediction, experimental confirmation, and its role in advancing atomic and molecular spectroscopy.

Findings

Discovery of the isotope effect in HCl molecules in 1920

Detection of atomic isotope effect leading to the discovery of deuterium in 1932

Illustration of the interplay between theory and experiment in spectroscopy

Abstract

The precise position of a spectral line emitted by an atomic system depends on the mass of the atomic nucleus and is therefore different for isotopes belonging to the same element. The possible presence of an isotope effect followed from Bohr's atomic theory of 1913, but it took several years before it was confirmed experimentally. Its early history involves the childhood not only of the quantum atom, but also of the concept of isotopy. Bohr's prediction of the isotope effect was apparently at odds with early attempts to distinguish between isotopes by means of their optical spectra. However, in 1920 the effect was discovered in HCl molecules, which gave rise to a fruitful development in molecular spectroscopy. The first detection of an atomic isotope effect was no less important, as it was by this means that the heavy hydrogen isotope deuterium was discovered in 1932. The early development of isotope spectroscopy illustrates the complex relationship between theory and experiment, and is also instructive with regard to the concepts of prediction and discovery.