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In thermal collisions between Xe(nf) Rydberg atoms and NH3 collisional depopulation of the nf state occurs through at least three distinct mechanisms: n-changing collisions, l-changing collisions, and ionizing collisions. Using selective field ionization we have measured the total collisional depopulation rate constants kd for laser-excited Xe(nf) atoms in the n range of 22 to 39. The magnitudes of kd are large, corresponding to reaction cross sections comparable to the geometric size of the Xe(nf) atom at n∼22. In the n range of 25 to 40, Xe+ ion production provides an absolute measure of the rate constants for collisional ionization. Approximate rate constants for n- and l-changing collisions are also presented for the 31f state. In these experiments we find that the state-changing collision rate constants are fairly independent of n and are determined largely by the l-changing collisions. The collisional ionization rate constants measured are smaller than the state-changing rate constants and increase with increasing n, ranging between 0.2 and 4.6×10−7 cm3/sec for n between 25 and 40. The present results are compared to those of recent theoretical calculations.

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Absolute rate constants for the ionization of highly excited xenon atoms in collisions with CH3I, C7F14, C6F6, and CH3Br have been measured and the major charged reaction products have been identified for all but CH3Br. Theoretical models view such collisions as being dominated by the interaction between the target molecules and the ’’essentially free’’ Rydberg electrons. It is thus predicted that the negative ions produced during collisional ionization are identical to those resulting from free electron attachment, and that the rate constants for collisional ionization are the same as those for free electron attachment. The present data are reviewed in light of these predictions.

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