The characteristic classes and Weyl invariants of Spinor groups

Based on a pair of cohomology operations on so called $\delta -2$-formal spaces, we construct the integral cohomology rings of the classifying spaces of the Lie groups $Spin(n)$ and $Spi{n}^c(n)$. As applications, we introduce characteristic classes for the reduced topological $K_{Spin}$ theory, determine the ring of integral Weyl invariants of the group $Spin(n)$, and demonstrate their usages in spin geometry.