On May 30, 1930, Bacher married Jean Dow. His mother gave them a Ford Model A and the use of the family's lakeside holiday house, where they entertained guests including Paul Ehrenfest and Enrico Fermi. In 1931, with a National Research Council Fellowship, he spent a year at the California Institute of Technology (Caltech) because Ira Bowen taught there. At Caltech Bacher attended lectures by Robert Oppenheimer, but spent most of his time at the Mt. Wilson Observatory, which had a better library. Bacher decided to create a work listing the energy, coupling constant, parity and electron configurations of all the known atoms and ions, working with Goudsmit back in Ann Arbor. The result was a book, Atomic Energy States as Derived from the Analysis of Optical Spectra (1932), which they dedicated to Randall.