An effective Hamiltonian method was used to deperturb the (X (2)Pi(i))4p sigma and (X (2)Pi(i))4p pi Rydberg states and the V(1)Sigma(+) valence state of HCl and DCl. A least-squares fit of the eigenvalues of the Hamiltonian to the experimental term energies was performed, and the zero-order diabatic characters of the basis states were determined. These deperturbed states were used to fit the observed h-doublings, to predict the energies of unknown states, to model spectroscopic intensity anomalies, and to explain the spin-orbit branching ratio for predissociation.