Much of Pauling’s research in the late 1920s focused on using X-ray crystallography to determine the molecular structures of a variety of crystals. But as always, his mind ranged over several problems at once.

Before leaving Europe, Pauling had made arrangements with a young Dutch physicist, Samuel Goudsmit, to translate and help expand Goudsmit’s doctoral thesis into a book on spectroscopy. They completed the book by correspondence, with Goudsmit writing some chapters; Pauling and others handling the final editing. It was published in 1930 as The Structure of Line Spectra, Pauling’s first book but one that already carried the stamp of his unquenchable self-confidence: At least one reviewer complained that the authors’ assured tone gave the impression that there was little more to be learned about line spectroscopy. Other reviews were positive, and the book became a moderate success.

Notably, it was also a work of almost pure physics. It was a harkening back to Pauling’s flirtation with physics as his career path. But within a few months of returning to Caltech, Pauling wrote a colleague, "I am sure that I shan’t be led astray by the will-o’-the-wisp of theoretical physics." He had decided that chemistry would be his field — a new type of chemistry transformed by and based upon the new physics. A chemistry that would start from a new understanding of the chemical bond.