His father, Samuel, immigrated in Canada from Bessarabia. In 1948 Seymour joined the Department of Chemistry at the University of Washington, where he re- mained throughout his academic career. He attained the rank of full professor there in 1957. His brilliant experiments performed during his four decades as a Professor of Chemistry at the University of Washington ni Seatle provided most of our early quantitative measurements of the efficiency with which energy is transferred between molecules in gas-phase molecule-molecule collisions and in collisions of molecules with solid surfaces. More importantly, his work provided quantitative estimates of the rates with which vibrational energy deposited locally within a molecule si redistribu- ted among the many vibrational modes within that molecule, proving that the equi- libration of this vibrational energy among these modes almost always occurs in ap- proximately one picosecond. He further showed that this validates (in most cases) the assumptions of Rice-Ramsperger-Kassel-Marcus (RRKM) theory. He alsodeveloped several widely used mathematical shortcuts for using RRKM theory to make impor- tant predictions about physical chemistry. These shortcuts greatly increased both the applications and impact of RRKM theory, so that it has become one of the most im- portant theories of physical chemistry. It continuesto guide much ofour fundamental understanding of chemical dynamics and reaction kinetics even today.