Arthur Erich Haas (30.04.1884-20.02.1941) was an Austrian theoretical physicist. He was born in Brno. He graduated from the University of Vienna (1906), where he worked (lecturer from 1912, professor from 1923); in 1913—14 he taught at the University of Leipzig. From 1935 he lived in the USA, and from 1936 he was professor at the University of Notre Dame.
His research was in the fields of spectroscopy, quantum theory, the structure of the atom and the history of physics. In 1910 he proposed a model of the atom in which he was the first to seek to connect the quantum character of radiation with the structure of the atom (the Haas model), and he obtained a quantitative relation between Planck's constant and the radius of the atom. Starting from his model, he calculated the Rydberg constant and Planck's constant. In 1920, independently of F. Loomis, he gave a formula for the isotope effect in rotational spectra.