At Caltech, Pauling struck up a close friendship with theoretical physicist Robert Oppenheimer, who spent part of his research and teaching schedule away from U.C. Berkeley at Caltech every year. Pauling was also affiliated to UC Berkeley as Visiting Lecturer in Physics and Chemistry from 1929 to 1934. Oppenheimer even gave Pauling a stunning personal collection of minerals. The two men planned to mount a joint attack on the nature of the chemical bond: apparently Oppenheimer would supply the mathematics and Pauling would interpret the results. Their relationship soured when Oppenheimer tried to pursue Pauling's wife, Ava Helen. When Pauling was at work, Oppenheimer came to their home and blurted out an invitation to Ava Helen to join him on a tryst in Mexico. She flatly refused, and reported the incident to Pauling. He immediately cut off his relationship with Oppenheimer.