Katheryn (Kathie) Marie Edmonds Rajnak (April 30, 1937 – February 3, 2005) was an American theoretical physical chemist who lived and worked in the United States. She was known for her work applying variations of the Hartree–Fock approach to calculating the energy levels of the lanthanide elements and their compounds. Applications of those results include the design of lasers for inertial-confinement fusion and for uranium isotope separation. She was the first woman to teach physics at Kalamazoo College, starting in 1967.