Molecular-tunneling spectroscopy in crystals with the use of a double-level-crossing technique

A method of measuring tunnel frequencies of molecular reorientation in crystals at low temperatures is demonstrated. Magnetic field variation brings the tunnel frequency to equality, first with the Larmor frequency of paramagnetic impurities and then with twice the Larmor frequency of protons whose magnetism has been saturated. In the first step paramagnetic ions cool the tunneling reservoir, and in the second the tunneling reservoir cools the proton Zeeman system, leading to enhanced proton relaxation.