Intramolecular spin relaxation probed by stern-gerlach experiments

Abstract

Abstract The phenomenon of intramolecular electron-spin relaxation (ISR) in isolated, collision-free molecules was studied by a Stern-Gerlach experiment in a molecular-beam apparatus. The relaxation was exhibited by a reduced Stern-Gerlach separation between molecules with different spin states induced by an inhomogeneous magnetic field as well as by the failure of the molecules to undergo refocusing by a second magnet with an opposite sense. Different degrees of Stern-Gerlach deflections were obtained for various molecules starting from normal behavior exhibited by NO 2 and MnCl 2 , partial deflections for nitroxyl radicals, nickelocene. CoBr 2 and CoCl 2 , and complete absence of Stern-Gerlach deflection for chromium(III) and iron(III) acetylacetonates, cobaltocene and various uranium halides. Thus, a correlation of the ISR with spin-orbit coupling and with the rotational and vibrational density of states was indicated. Using a statistical model, an estimation for the spin-relaxation times could be obtained for the nitroxyl radicals. They were 0.5 μs and 7 ns for TEMPO (2.2.6.6-tetramethylpiperidinooxyl) and DTBN (di-tert-butyl nitroxyl) radicals respectively in effusive molecular beams, while for the cold molecules in a seeded supersonic beam they were = 350 μs and slightly longer for these two radicals respectively. The implications of ISR to other experiments, especially those which are using Stern-Gerlach type of experiments are discussed.