Measurement of the branching fractions for D/sup 0/. --> pi. /sup -/e/sup +/. nu. /sub e/ and D/sup 0/. -->. K/sup -/e/sup +/. nu. /sub e/ and determination of chemically bondV/sub c//sub d//V/sub c//sub s/chemically bond/sup 2/

Measurements of the exclusive branching fractions B(D/sup 0/..--> pi../sup -/e/sup +/..nu../sub e/) and B(D/sup 0/..-->..K/sup -/e/sup +/..nu../sub e/), using data collected at the psi(3770) with the Mark III detector at the SLAC e/sup +/e/sup -/ storage ring SPEAR, are used to determine the ratio of the Kobayashi-Maskawa matrix elements chemically bondV/sub c//sub d//V/sub cs/chemically bond/sup 2/ = 0.057 +- /sup +0.038//sub 0.015/ +- 0.005.