A new method for simulating the effect of outgoing-wave boundary conditions in the calculation of quantum resonances is presented. The Hermitian Hamiltonian operator H is multiplied on each side by a damping operator D, consisting of areal function d(R), which is unity in the resonance region and falls gradually to zero in the asymptotic region. The spectrum of the symmetrically damped Hamiltonian operator, DHD is shown to provide an excellent approximation to the resonance energies of the Hamiltonian with outgoing-wave boundary conditions. Applications to the calculation of resonance energies for collinear H+H-2 scattering and for HO2 dissociation are presented. In addition, we explore the feasibility of extracting resonance widths by using the DHD operator within a filter diagonalization (FD) scheme. Application of the FD scheme to HO2 yields encouraging results. (C) 1997 American Institute of Physics. [S0021-9606(97)02447-1].