THE AUTOMORPHISMS OF NON-DEFECTIVE ORTHOGONAL GROUPS Ω8（V）AND O’8（V）IN CHARACTERISTIC 2

Let V be a non-defective 8-dimensional quadratic space over a field F of characteristic2,F≠F2.We prove that if there is an exceptional automorphism of either Ω8（V）orO’8（V）,then Va has a Cayley algebra structure for some a in .Moreover,everyexceptional automorphism of O’8（V）as exactly one of the following forms:1°Φg or 2°Φg,where Φg is an automorphism of O’8（V）given by conjugation by a semilinear automorphismof V which preserves the quadratic structure,and 1 and 2 are the automorphismsinduced by triality principle.Every exceptional automorphism of Ω8（V）is the restrictionof a unique exceptional automorphism of O’8（V）.