"I slept till very late in the morning, found I couldn’t do work at all, had a quick lunch, went to sleep again in the afternoon and slept until five o’clock. When I woke up...I had clearly...the picture before me of the two wave functions of two hydrogen molecules joined together with a plus and minus and with the exchange in it. So I was very excited, and I got up and thought it out. As soon as I was clear that the exchange did play a role, I called London up, and he came to me as quickly as possible. Meanwhile I had already started developing a sort of perturbation theory. We worked together then until rather late at night, and then by that time most of the paper was clear.... Well...at least it was not later than the following day that we had the formation of the hydrogen molecule in our hands, and we also knew that there was a second mode of interaction which meant repulsion between two hydrogen atoms, also new at the time –- new to chemists, too."

Walter Heitler. AHQP (Archive for the History of Quantum Physics), volume 6. March 18, 1963.

"The paper of Heitler and London on H₂ for the first time seemed to provide a basic understanding, which could be extended to other molecules. Linus Pauling at the California Institute of Technology in Pasadena soon used the valence bond method. . . . As a master salesman and showman, Linus persuaded chemists all over the world to think of typical molecular structures in terms of the valence bond method."

Robert Mulliken. Life of a Scientist, pp. 60-61. 1989.