Aerodynamic focusing of heavy molecules in seeded supersonic jets
The phenomenon of aerodynamic enrichment of heavy molecules seeded in supersonic free jets has been known since 1955. But its systematic exploitation in the generation of intensely focused molecular beams has been prevented by the lack of a quantitative and realistic explanation of the observed facts. Here, the aerodynamic focusing of CBr/sub 4/, W(CO)/sub 6/, and C/sub 2/Cl/sub 6/ molecules seeded in jets of He or H/sub 2/ is studied experimentally, and found to be most singular under conditions similar to those known to produce sharply focused beams of microscopic spheres suspended in air jets. The gas mixture expands through thin-plate orifice into a vacuum chamber, forming a supersonic free jet. The spacial distribution of the heavy molecules in the jet is measured at varying distances /ital L/ to the nozzle by scanning a thermocouple probe across a jet diameter. The probe is sufficiently small to interfere negligibly with the flow. The increment DV in the thermocouple voltage resulting from seeding the heavy gas on a given flow of He or H/sub 2/ is seen to be a sensitive indicator of the local concentration of seed molecules in the jet. The following behavior is observed in terms of the same Stokes number or inertia parameter /ital S/ that governs the simpler and better understood phenomenon of aerosol focusing. Below /ital S/=0.4 for H/sub 2/ and /ital S/=0.2 for He, heavy molecule and aerosol beam widths are practically identical, and the boundary of the jet of heavy molecules is rather sharp. At higher values of /ital S/, aerosol beams show further reductions
- Research Organization:
- Yale University, Department of Mechanical Engineering, New Haven, Connecticut 06520(US)
- OSTI ID:
- 5976183
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 91:4; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AERODYNAMICS
BEAMS
BROMINATED ALIPHATIC HYDROCARBONS
CARBONYLS
CHLORINATED ALIPHATIC HYDROCARBONS
DISTRIBUTION
ELEMENTS
FLUID FLOW
FLUID MECHANICS
FLUIDS
FOCUSING
GASES
HALOGENATED ALIPHATIC HYDROCARBONS
HELIUM
HYDROGEN
JETS
MECHANICS
MOLECULAR BEAMS
NONMETALS
ORGANIC BROMINE COMPOUNDS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
RARE GASES
REFRACTORY METAL COMPOUNDS
SPATIAL DISTRIBUTION
SUPERSONIC FLOW
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS