HAL Id: jpa-00217049
https://hal.archives-ouvertes.fr/jpa-00217049
Submitted on 1 Jan 1977
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
ELECTRON DIFFRACTION STUDIES OF
CLUSTERS FORMED IN SEEDED NOZZLE BEAMS
P. Jeuck, G. Stein
To cite this version:
JOURNAL DE PHYSIQUE Colloque C2, suppldment a u no 7 , Tome 38, Juillet 1977, page C2-53
ELECTRON DIFFRACTION STUDIES OF CLUSTERS FORMED
IN SEEDED NOZZLE BEAMS
(*)
P. R. JEUCK, 3rd and G. D. STEIN
Northwestern University, Gasdynamics Laboratory, Evanston, Illinois 60201,
USA
Abstract. - A multistage molecular beam has been constructed to provide a continuous supply of clustered species into a torr scattering chamber where the beam is crossed with a 40 keV electron beam. Diffraction patterns from the molecular beam are magnetically scanned over a scintillator-photomultiplier detector. The molecular beam is mechanically chopped and patterns taken in either an analog mode using a lock-in amplifier, or in a digital pulse counting mode. The pulse counting scheme provides equal time windows when the molecular beam is on and off eliminating the shutter opening and closing parts of the cycle. Since one scattered high energy electron can produce many photons, single photon noise events can be discriminated against using a pulse height analyzer.
Experiments are carried out in two modes. One is the conventional mode of expanding an unsaturated gas mixture through the nozzle where the nucleation occurs in the free jet expansion. The other mode, for metals, consist of mixing with a cold carrier gas just prior t o the nozzle expansion causing nucleation before the free jet formation. The mean cluster size is varied by changing the temperature, pressure and condensable species mole fraction. Diffraction patterns, for H20 and for COz in the former mode, and Ag plus Ar in the latter mode, will be presented and the resultant cluster size and structure discussed.
(*) The partial support of this work by the Office of Naval Research and by the National Science Foundation is gratefully acknowledged.
