Molecular-Beam Resonance Method With Zeeman-Decelerated Samples: Application To Metastable Helium Molecules

We use a multistage Zeeman decelerator to generate slow beams (upsilon similar or equal to 100 m/s) of translationally cold, spin-polarized metastable a (3)Sigma(+)(u) He(2 )molecules and perform a precision measurement of their spin-rotation fine structure. The spin polarization results from the elimination of the high-field-seeking J = N spin-rotational component of each rotational level (rotational quantum number N) by the Zeeman deceleration process. By repopulating the J = N component from the J = N +/- 1 low-field-seeking components using radio-frequency radiation, we measured the spin-rotation fine structure of 13 rovibrational levels with upsilon = 0, 1 and N = 1-21. The low beam velocity and the resulting long interaction times with the radio-frequency radiation were exploited to determine the transition frequencies with a precision of 300 Hz.