William Klemperer

William Aloys Klemperer (October 6, 1927 – November 5, 2017) was an American chemist, chemical physicist and molecular spectroscopist. Klemperer is most widely known for introducing molecular beam methods into chemical physics research, greatly increasing the understanding of nonbonding interactions between atoms and molecules through development of the microwave spectroscopy of van der Waals molecules formed in supersonic expansions, pioneering astrochemistry, including developing the first gas phase chemical models of cold molecular clouds that predicted an abundance of the molecular HCO+ ion that was later confirmed by radio astronomy.