Intramolecular Spin Relaxation in Isolated Molecules

We report an experimental observation of intramolecular electron-spin relaxation in isolated, collision-free molecules, in a molecular-beam apparatus. The relaxation was probed by a Stern-Gerlach experiment with Rabi-type inhomogeneous magnets. Relaxation was found to be very efficient for molecules such as chromium acetylacetonate and U${\mathrm{Cl}}_4$. For the nitroxide free radical TEMPO (2,2,6,6-tetramethylpiperidinooxy) relaxation times of about 0.4 and 200 μs were found in effusive and supersonic beams, respectively.