HEXAPOLE-SELECTED SUPERSONIC BEAMS OF REACTIVE RADICALS - CF3, SIF3, SH, CH, AND C2H

A supersonic corona discharge source was used to produce molecular bea ms of plasma particles. Neutral, polar components of the plasma mixtur e were selectively focused by an electrostatic hexapole, thereby ''sim plifying'' the chemical and rotational state composition of the beam. Careful choice of a radical precursor, combined with control of discha rge and hexapole voltage allowed the production of pure beams of CF3, SiF3, and SH (purity typically better than 90%), with no noticeable si gnal arising from undissociated precursor, ions, or other radicals. Fo cused beams from a hydrocarbon plasma contained a radical mixture of p redominantly CH and C2H. Radical beams were characterized by rotationa lly and translationally cold temperatures (typically T-R < 20 K and T- S < 20 K, respectively) and high intensities (typically 10(11)-10(12) cm(-2)s(-1)). Simulated focusing spectra using classical trajectory ca lculations showed generally good agreement with the experimental data, leading to the first experimental measurement of the permanent electr ic dipole moment of SiF3 (mu = 1.2+/-0.1 D). (C) 1998 American Institu te of Physics.