Rcccued
-l August 198 I, MI tin.rl iorm 17 September 198 I A gener.rllzed Langcvm cquatron, based on a pseudo-Lrouvrllc representation of hard-spbcrc dynsmrcs. ts uwd to c~anunr the hmcrrc energy relJ\atron TJIC cochicrcnr.b,. of J sphcrrnl broa nun pa, trclc m a drluce ~3s In the hmn of 3 brfc and massrvc test p~ruclc. we find hE = 1~Jft1,. w hcrc ts IS the S~ohes' law friction and rrrr IS rhe m.ru of IIIC broonwn ~JIIICIC I. lntroductron The success of hydrodynamrcal tlteortes rn descrrbmg molecular matron has prompted a considerable research mterest m thts phenomenon, leading to a number of mrcroscoplc derrvatrons of the force and torque exerted by a flmd on a movtng sphertcal browntan (B-) part& from kmetrc [ 1,2] and mode couphng theory vrewpomts [2.3]. A comprehcnsrve theory of self-dtffuston m a dense sample fltnd as yet rematns to be formulated. Of related interest IS the relaxatron of a B-partrcle's kmettc energy, I e. the manner m which the tagged partmle's translatronal energy IS dlssrpated among the bath molecules The interplay between colhstonal and collecttve effects IS quite subtle for the energy relalatron problem For example, kmettc and mrcroscoprc boundary layer theory methods have been used to show that the ktnettc energy rclaxatron rate constant, k,, takes the form