Free isometric actions on the affine space Qn

We will show that for every integer n greater than or equal to 3 there exists a free non-abelian group of linear isometrics of the vector space Q(n) such that any subgroup fixing any point (mu) over right arrow not equal (0) over right arrow of Q(n) is cyclic. Recall that two elements of F-2 commute if and only if they belong to a cyclic subgroup of F-2.