We present experimental results on the collision of large binary noble gas
clusters with a hot graphite surface at an incident velocity of 430 ms(-1).
The mixed ArnXm clusters (X=Kr, Xe) with average sizes n+m between 1000 an
d 13 000 are obtained from pure argon clusters by the pickup technique. The
surface scattering dynamics belongs to the thermal evaporation regime and
large surviving binary fragments are detected at grazing angles. As expecte
d from simple binding energy considerations, in all cases the surviving clu
sters are richer in the dopant species X. This enrichment has been measured
as a function of incidence angle, incident cluster size, and dopant molar
fraction x. For the lowest values of x (about 0.7%), the measured enrichmen
t is the same for Kr and Xe, and decreases slowly with increasing size and
incidence angle. On the other hand, when x is raised up to 15%, this enrich
ment decreases substantially for Xe, and much less for Kr. This unexpected
behavior clearly shows that collision induced evaporation cannot be viewed
as a mere distillation of an homogeneous binary mixture. The possible role
of the incoming cluster structure is discussed in connection with the prepa
ration of the binary clusters by pickup. (C) 1999 American Institute of Phy
sics. [S0021-9606(99)01805-X].