Molecular beam focusing of ICl in rotational states with positive induced electric dipole moments

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Abstract
Molecular beams of ICl in selected rotational states with positive effective electric dipole moments have been produced using a new electrostatic alternate gradient focuser (AGF). It has been possible to select the states ‖J,M〉=‖0,0〉, ‖1,±1〉, and ‖2,±2〉. The experimental arrangement consists of a seeded supersonic nozzle beam source for ICl, the AGF selector based on four‐wire fields, and a quadrupole mass filter detector with electron bombardement ionizer. The velocity selector, usually used in state selection experiments, could be eliminated because of the narrow velocity distribution (Δv/v?0.05) of the ICl beam. On account of the strong rotational cooling during the nozzle beam expansion, the relative populations of lower J states are increased substantially. An additional advantage of the seeded beam technique is the possibility of changing the velocity of the state‐selected molecules by choosing a suitable noble gas mixture. The flux density of the state‐selected ‖1,±1〉 beam exceeds that of the direct unfocused beam; its absolute value is estimated to be greater than 3×1012 molecules cm−2 s−1.