Nonfactorizable contributions to hadronic decays of charm mesons in the Cabibbo-suppressed modes

We investigate nonfactorizable contributions to charm meson decays into D --> pi pi/K (K) over bar/K (K) over bar*/(K) over bar K*/D --> K''(K) over bar* modes. Obtaining the contributions from spectatorquark diagrams for N-c = 3, we determine the nonfactorizable isospin amplitudes required to explain the data for these modes. For these decays, we observe that pi pi, np, decay modes favor a nonfactorizable-isospin-amplitudes ratio A(0)(nf)/A(2)(nf) equal to (1.123 +/- 0.158) and for K (K) over bar, K (K) over bar*, (K) over bar K* and K*(K) over bar* modes, the ratio of nonfactorizable amplitudes A(0)(nf) and A(1)(nf) turns out to be unity.