title: Cold and intense OH radical beam sources.
abstract: We present the design and performance of two supersonic radical beam sources: a conventional pinhole-discharge source and a dielectric barrier discharge (DBD) source, both based on the Nijmegen pulsed valve. Both designs have been characterized by discharging water molecules seeded in the rare gases Ar, Kr, or Xe. The resulting OH radicals have been detected by laser-induced fluorescence. The measured OH densities are (3.0 ± 0.6) × 10(11) cm(-3) and (1.0 ± 0.5) × 10(11) cm(-3) for the pinhole-discharge and DBD sources, respectively. The beam profiles for both radical sources show a relative longitudinal velocity spread of about 10%. The absolute rotational ground state population of the OH beam generated from the pinhole-discharge source has been determined to be more than 98%. The DBD source even produces a rotationally colder OH beam with a population of the ground state exceeding 99%. For the DBD source, addition of O2 molecules to the gas mixture increases the OH beam density by a factor of about 2.5, improves the DBD valve stability, and allows to tune the mean velocity of the radical beam.
authors.affiliation: Institute for Molecules and Materials, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors.forename: Ludger
authors.initials: L
authors.lastname: Ploenes
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Haas
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
authors.forename: Dongdong
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Institute for Molecules and Materials, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors.forename: Sebastiaan Y T
authors.initials: SY
authors.lastname: van de Meerakker
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Willitsch