MAGNETIC ANALYSIS OF NEARLY EFFUSIVE AND MODERATELY SUPERSONIC BEAMS OF OXYGEN MOLECULES

We report here experimental results on the magnetic analysis of velocity-selected molecular beams of oxygen using mass spectrometric detection. The experimental configuration allows us to establish a connection between the transmittance of the beam as a function of magnetic field intensities and the rotational distribution of the molecules. It is found that rotational temperatures can be usefully defined to describe distributions of the rotational angular momentum of an O-2 molecule when beams are moderately supersonic (non-statistical behavior and alignment effects occurring under the extreme cooling conditions of highly supersonic expansions are considered elsewhere [38]). Most results can be explained assuming adiabatic adjustment of effective magnetic moments as molecules enter the magnetic field, but evidence is put forward that nonadiabatic effects can be of importance for sudden passages at high velocities and fields. The technique is also shown to be of use for diagnostic purposes in the specific case that the nearly effusive beam is heated under microwave discharge leading to an estimate of the role of metastable molecular states produced under such conditions.