Wuhan Univ, Dept Phys, Wuhan 430072, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
Using the leading-order low-energy effective Hamiltonian, we calculate B-c --> PP (where P stands for pseudoscalar meson) decays induced by pure W-emission mechanisms. In order to estimate the hadronic matrix elements, we apply the perturbative quantum chromodynamics (PQCD) method proposed by Szczepaniak et al. [Phys. Lett. B 243 (1990) 287] and developed by Simma et al. [Phys. Lett. B 272 (1991) 395]. Compared with the predictions of other models, we find that the PQCD method is suitable for these decays and therefore the spectator ansatz seems questionable.