| eQq | 
          Qudrupole Coupling Constant | 
        
        
          | eQq2 | 
          Extra Qudrupole Coupling Constant for degenerate states;
            This
            is defined by analogy with eQq2 in linear molecules, and
            gives the same
            matrix elements within K
            =
            ±1
            states as in Λ = ±1 states for linear
            molecules.  | 
        
        
          | Czz | 
          Component along symmetry axis of Nuclear Spin - Rotation
            interaction. | 
        
        
          | Cperp | 
          Average of components perpendicular to symmetry axis of
            Nuclear Spin - Rotation interaction. |