Energy transfer and chemical reaction resulting from the impact of molecular beams upon surfaces
Platinum detectors with shiny and black surfaces are placed in the path of intense molecular beams of He, Ar, H{sub 2}, N{sub 2}, and SF{sub 6} which are generated through supersonic expansion from nozzles at a known temperature. The detectors have relatively large surface areas (about 0.2 x 0.2 cm{sup 2}) compared to the total cross section of the three fine thermocouple wires (diameter 0.025 mm) that support each of them. Thus a relatively large number of beam molecules can transfer energy to the surfaces, while the heat loss through conduction is made relatively small. The mass of the Pt surfaces is small so that their temperature reaches steady state in about three minutes. For a nozzle at room temperature and a shiny Pt surface initially also at room temperature, the thermocouple records temperature rises that for pure gases are as large as 30 K, and for binary mixtures exceed 110 K. He also observes temperature rises of the Pt surfaces due to energy transfer from vibrationally excited SF{sub 6} molecules produced by irradiation with a CO{sub 2} laser. He proposes a mechanism to account for the temperature rises during the interaction of the beam molecules with the surfaces. He has used a compound called hexafluoroDewarbenzene (HFDB) to study the effect of the kinetic energy of the incident beam on the rate of the isomerization to hexafluorobenzene (activation energy is 118 KJ/mole), initiated by collision of the molecule with various surfaces. This HFDB is accelerated using the seeded beam technique to a kinetic energy as high as 230 KJ/mole before its collision with the surfaces. The results, as yet not understood, show that slower HFDB molecules produced by seeding into Ar produce more reaction than faster molecules produced by seeding into H{sub 2} or He.
- Research Organization:
- Brown Univ., Providence, RI (USA)
- OSTI ID:
- 5830376
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201 -- Chemical & Physicochemical Properties
656003* -- Condensed Matter Physics-- Interactions between Beams & Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ARGON
AROMATICS
BEAMS
CHEMICAL REACTIONS
COLLISIONS
ELEMENTS
ENERGY TRANSFER
FLUIDS
FLUORIDES
FLUORINE COMPOUNDS
GASES
HALIDES
HALOGEN COMPOUNDS
HEATING
HELIUM
HYDROGEN
ISOMERIZATION
MASS
METALS
MOLECULAR BEAMS
MOLECULE COLLISIONS
NITROGEN
NONMETALS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PLATINUM
PLATINUM METALS
RARE GASES
STEADY-STATE CONDITIONS
SULFUR COMPOUNDS
SULFUR FLUORIDES
TRANSITION ELEMENTS