χ J (ϕ ± 4π) = +χ J (ϕ) ; (an integer/a half-integer J), In the non-relativistic (NR) case, the molecular symmetry is described by the spatial symmetry and the electronic orbital angular momentum (M J = M L ). In thfis case, the quantum number (J = L) is an integer, and rotation by 2π returns the system to the original state (eq 4). That is, rotation by 2π is equivalent to the identity operator Ê. This is the case of a normal point group. Meanwhile, in the relativistic case, the projection of the total angular momentum M J = M L +M S is a good quantum number, and J becomes a half-integer when the system contains an odd number of electrons. Here, rotation by 2π reverses the sign (eq 5). In both cases, Rϕ=4π = Ê is satisfied.