Isomorphy Classes of $k$-Involutions of $\text{SO}(n, k,\beta)$, $n > 2$
  A first characterization of the isomorphism classes of $k$-involutions for any reductive algebraic group defined over a perfect field was given in \cite{Helm2000} using $3$ invariants. In \cite{HWD04,Helm-Wu2002} a full classification of all $k$-involutions on $\text{SL}(n,k)$ for $k$ algebraically closed, the real numbers, the $p$-adic numbers or a finite field was provided. In this paper, we find analogous results to develop a detailed characterization of the $k$-involutions of $\text{SO}(n,k,\beta)$, where $\beta$ is any non-degenerate symmetric bilinear form and $k$ is any field not of characteristic $2$. We use these results to classify the isomorphy classes of $k$-involutions of $\text{SO}(n, k,\beta)$ for some bilinear forms and some fields $k$. 
Robert W. Benim, Christopher E. Dometrius, Aloysius G. Helminck, Ling   Wu
math.RT