Perturbed states representing the response to an external electric field are obtained from multi-reference configuration interaction wavefunctions. The multi-configurational reference function is designed to represent the ground state as well as the perturbed and even the first excited states on equal footing, i.e., orbital optimization is performed in a perturbed multi-reference self-consistent field procedure. For various perturbing operators, several perturbed wavefunctions for different frequencies of the perturbing field are obtained simultaneously with the corresponding lowest excited state. From these sets of perturbed and excited states, reduced spectra are derived which represent effective oscillator strength distributions and serve to calculate dynamic polarizabilities. hyperpolarizabilities, and long-range interaction coefficients. The results for both the dynamic polarizabilities and the interaction coefficients are found to be in excellent agreement with experimental data and other accurate theoretical values.