Measurements of the absolute branching fractions for D->Kbar pi e+ nu_e, D-> K*bar e+nu_e and determination of Gamma(D+ -> K*0bar e+ nu_e)/Gamma(D+ -> K0bar e+nu_e)

Using the data of about 33 pb$^{-1}$ collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays $D^+ \to K^-\pi^+ e^+\nu_e$, $D^0 \to \bar K^0\pi^-e^+\nu_e$, $D^+ \to \bar K^{*0}e^+\nu_e$ and $D^0 \to K^{*-}e^+\nu_e$. The absolute branching fractions for the decays are measured to be ${BF}(D^+ \to K^-\pi^+e^+\nu_e)=(3.50\pm0.75\pm0.27)%$, ${BF}(D^0 \to \bar K^0\pi^-e^+\nu_e)=(2.61\pm1.04\pm0.28)%$, ${BF}(D^+ \to \bar K^{*0}e^+\nu_e)=(5.06\pm1.21\pm0.40)%$ and ${BF}(D^0 \to K^{*-}e^+\nu_e)=(2.87\pm 1.48\pm 0.39)%$. The ratio of the vector to pseudoscalar semileptonic decay rates $\Gamma(D^+\to\bar K^{*0}e^+\nu_e)/\Gamma(D^+\to\bar K^0e^+\nu_e)$ is determined to be $0.57\pm0.17\pm0.02$.