ROTATIONAL ALIGNMENT IN SUPERSONIC SEEDED BEAMS OF MOLECULAR-OXYGEN

The ''seeding'' phenomenon associated with the supersonic expansion of gaseous mixtures into a vacuum leads to cooling of the molecular degr ees of freedom and also to alignment of the rotational angular momentu m. Exploiting magnetic analysis of supersonic seeded beams of O-2 from various gaseous mixtures with rare gases and from air near atmospheri c pressure, we demonstrate that the phenomenon naturally leads to excl usive population of the ground rovibrational triplet state and also to strong rotational alignment. The observation is also made that the al ignment depends on the final speed, so that within the same beam, mole cules traveling faster show much greater alignment than slow ones. The dependence of the effect on the gas carrier and on pressure and compo sition of the mixtures has also been investigated.