Rotor accelerated molecular beams

Abstract

Ultra-high-speed rotors constructed from carbon fibre composite material have been employed to generate supersonic molecular beams travelling at velocities ⩽ 2 km s^–1. Beams have been generated from molecules ranging in molecular weight from H₂O to W(CO)₆ and chemical activity from Ne to I₂; peak fluxes are ∼10¹⁷ molecule steradian^–1s^–1 corresponding to ∼10¹⁰ molecule pulse^–1. A kinetic model which describes all the observed beam characteristics has been developed; all the results can be understood by assuming that the molecules are fully accommodated at the advancing rotor surface and leave with a net velocity compounded from that of the rotor tip and the Maxwellian thermal velocity at the surface temperature. The potential utility of rotor accelerated beams is indicated; in some applications they offer advantages over conventional nozzle-beam sources, particularly when it is important for the beam to be composed of a single molecular species.