Computational Study of the Mono- and Dianions of SO\\r sub/2sub\\r , SO\\r sub/3sub\\r , SO\\r sub/4sub\\r , S\\r sub/2sub\\r O\\r sub/3sub\\r , S\\r sub/2sub\\r O\\r sub/4sub\\r , S\\r sub/2sub\\r O\\r sub/6sub\\r , and S\\r sub/2sub\\r O\\r sub/8sub