Characterization of oriented molecule beams by radio frequency spectroscopy

Molecular-beam electric-resonance spectroscopy is used to interrogate the rotational states present in a molecular beam of oriented symmetric-top molecules produced for scattering experiments, Delta M = +/-1 transitions are observed between Stark energy levels in weal; electric fields and depend on the rotational quantum numbers J and K. Substantial rotational cooling is apparent in both neat and seeded beams. Each resonance signal has a complicated dependence upon the high voltage applied to the hexapole focusing fields because molecules in the newly transformed states have vastly different focusing properties from the original. These effects can be unified using a "reduced" focusing voltage that allows intensity comparisons between rotational states, giving rotational temperatures of 3-4 K for CF3H seeded in He or Ar. Under favorable circumstances, radio frequency "labeling" might: allow one to selectively remove one rotational level at a time from an oriented molecular beam and thereby to study the orientation dependence of different rotational states.