Current-voltage characteristics of drifting spherical Langmuir probes have been studied experimentally in collisionless plasmas. In order to single out the effect of probe speed on the ion current collection, the experiment was carried out by a rotating arm facility. With this device the probe speed as well as the properties of the undisturbed plasma were accurately determined. As predicted by the theories of Kanal, Godard, and Laframboise, the ion current at small speed ratios was found to be either increased or decreased as the probe speed increased depending on the ratio of probe radius to Debye length R/λD. As for the absolute magnitude of ion current change by the probe speed, however, discrepancies were found between these theories and the present experiment. The difference is considered to originate from asymmetry in the potential distribution, which is not included in these theories.

The orientation dependence of the CF3* formation was investigated for two collisional energy transfer reactions, CF3C1 + AI-(~P) and CF3Br + Kr(3P>, and the results were compared with that of a related CF3H + Ar(3P) reaction which was previously studied. For the three systems studied, the reactivity was found to be the greatest for collisions at the CF3 end of the molecules. The CF3C1 + Ar(3P) system exhibited a steric opacity function with two reactive sites. The CF3Br + Kr(3P) system showed a broad steric opacity function as compared with the other two systems. This broadness of the steric opacity function is discussed in terms of the effect of the center-of-mass shift in the molecular frame and/or of impact parameter broadness.

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