  We present methods for accurate evaluation of van der Waals coefficients of
dimers with excited atoms that have a strong decay channel. We calculate C_6
coefficients for the Yb-Yb 1S_0+ 3P_{0,1}, 3P_0+3P_0 and Yb-Rb 3P_1+5s, 1S_0+
5p_{1/2} dimers and C_8 coefficients for the Yb-Yb 1S_0+1S_0, 1S_0+3P_1 and
Yb-Rb 1S_0+5s dimers. We evaluate uncertainties of all properties.
