“Über die Spektra von Atomsystemen mit zwei Elektronen.” Contained in Zeitschrift für Physik, Vol. 39, Berlin, Julius Springer, 26 October, 1926, pp. 499-518.
Very good. With the pencil signature of Nobel Laureate John H. Van Vleck. Contemporary blue buckram, with title, issue, and year in gilt on spine. Octavo. All attempts to explain the helium spectra using the old quantum mechanics of Bohr and Sommerfeld had failed. Incorporating both Pauli’s exclusion principle and.....