The Guggenheim Trip, Part II: The Growth of a Scientist

Linus Pauling, Werner Kuhn, and Wolfgang Pauli traveling by boat in Europe. 1926.

“My year in Munich was very productive. I not only got a very good grasp of quantum mechanics — by attending Sommerfeld’s lectures on the subject, as well as other lectures by him and other people in the University, and also by my own study of published papers — but in addition I was able to begin attacking many problems dealing with the nature of the chemical bond by applying quantum mechanics to these problems.”
– Linus Pauling. The Chemical Bond: Structure of Dynamics, Ahmed Zewail, ed. 1992.

After his and Ava Helen’s stay in Italy, Linus Pauling was itching to return to the lab. The couple arrived in Munich in the last week of April and the first item on Pauling’s agenda was a meeting with Arnold Sommerfeld.

Sommerfeld, in association with Niels Bohr, was responsible for the Bohr-Sommerfeld model of the atom, a precursor to modern quantum mechanical ideas on atomic structure. At the time of Pauling’s European trip, Sommerfeld was serving as the director of the Institute of Theoretical Physics in Munich. He had spent the past decade building Germany’s community of physicists, nuturing many of Europe’s best scientists on a steady diet of cutting edge research. His lectures, famous by the time Pauling reached Europe, were known for their new and innovative content. As Thomas Hager, a Pauling biographer, explains, “[Sommerfeld] knew everyone in theoretical physics, had collaborated with many of them and corresponded regularly with the rest.” He knew exactly what was happening in his field and made sure his students did too.

Pauling’s first Munich meeting with Sommerfeld was something of a disappointment for the young scientist. Rather than being allowed to continue the work he had begun at Caltech, Sommerfeld chose to assign Pauling mathematical research relating to electron spin – an area that held little interest for him.

After a spell of half-hearted devotion to the electron spin problem, Pauling convinced Sommerfeld to allow him to study the motion of polar molecules. Pauling believed he could clarify portions of the Bohr-Sommerfeld model by introducing the effects of a magnetic field to the existing equations. This caught Sommerfeld’s attention and Pauling was subsequently instructed to continue his research under the stipulation that he provide Sommerfeld with the details of his work for presentation at an upcoming conference in Zurich. Pauling did so, and a few days after Sommerfeld had departed for the conference, he received an order to appear in Zurich to discuss his work.

Once at the conference, Pauling found himself surrounded by the leading physicists of Europe. Wolfgang Pauli, a young German physicist famous for his development of the revolutionary Pauli Exclusion Principle, was among those in attendance. On a whim, Pauling approached his colleague and began explaining his recent work on the Bohr-Sommerfeld model. Pauli was unimpressed. The paradox-riddled Bohr-Sommerfeld model, and Pauling’s work supporting it, was on its way out with the new ideas of quantum mechanics soon to take its place. Pauling’s research was too late to be of any value and Pauli was not shy about telling him so.

After finishing his summer vacationing with Ava Helen in Switzerland, Pauling returned to Munich for the fall semester. It was at this time that Pauling really began to prove himself, developing a reputation for his extensive knowledge and concentrated enthusiasm. Pauling’s most important accomplishment, however, was not his ability to make friends. Instead, it was gaining both the attention and the esteem of Arnold Sommerfeld. Pauling did so by discovering a mathematical error in the work of Gregor Wentzel, a protégé of Sommerfeld. The discovery and correction of this mistake garnered Pauling a great deal of respect in Sommerfeld’s eyes.

As it turned out, Pauling’s discovery of Wentzel’s error resulted in more than just Sommerfeld’s acclaim. It allowed Pauling to apply Wentzel’s work to the calculation of energy levels, which in turn provided the platform for a series of calculations on the energy values for complex atoms. This was a totally new approach to deriving atomic properties and Pauling took full advantage of his discovery, publishing his findings in a paper titled “The Theoretical Prediction of the Physical Properties of many-Electron Atoms and Ions.”

In a matter of months, Pauling had evolved from a star-struck young American to a legitimate player in the European field of quantum mechanics. Fortunately for him, his rise to scientific prominence had only just begun.

Read about Arnold Sommerfeld in “The Duelist” or learn more about this entire story on the website “Linus Pauling and the Nature of the Chemical Bond: A Documentary History.”