x exp(-x[2cos cos0'-sin @sin'cos(-)]), x≡mm'/kTR3 where is considered to be a small quantity.The (4r)2 expansion with respect to xyields the contribution in zeroth order and no contribution in first order.The second order contribution is found to be 5∫daos0jde厂∫deas0 d/Bow0cos9-sin0sin9 'cos-P =号a号 (114 Thus we finally obtain for the partition function Z≈(4P(1+3T西 1m2m2 (115) The mean force may be found with the help of the relation (可=kT 0 In Z. OR (116) Solution 2 Fromwhere is considered to be a small quantity. The expansion with respect to yields the contribution in zeroth order and no contribution in first order. The second order contribution is found to be (114 ) Thus we finally obtain for the partition function (115) The mean force may be found with the help of the relation (116) Solution 2 From