MBMS SAMPLING FROM HIGHLY HEATED GAS-MIXTURES (1000-3000 K) AND WEAKLY IONIZED RF PLASMAS (800-2800 K) OR LASER PLASMAS (5008-20000 K)

Molecular beam mass spectrometric (MBMS) sampling is often used in ana lysis techniques, applied mainly to heated gaseous media. The present paper shows the efficiency of the method, but also the difficulties oc curing from the distortions that may be introduced in the properties o f the molecular beam by the sampling procedure itself. Condensation ph enomena, background gas penetration, shock structure, aerodynamic sepa ration effects, skimming process can be responsible of important distu rbances. The means for avoiding or minimizing these drawbacks are exam ined, especially in the case of molecular beams skimmed from free jets generated at high temperature. Different heating techniques are studi ed : gas heated in an oven (1000-3000 K), plasma generated in a radio- frequency discharge (800-2800 K), plasma sustained by laser power abso rption (5000-20000 K).