Solution
= Solution
\b[$k_Q=9.9\times10^4\ \mathrm{dm^3\,mol^{-1}\,s^{-1}}$.] The unquenched triplet lifetime is
$$
\tau_0=\frac1{180+18}=5.05\times10^{-3}\ \mathrm s.
$$
Since the slope is $k_Q\tau_0$, the bimolecular <rate constant> is
$$
\boxed{k_Q=(5.0\times10^2)(198)=9.90\times10^4\ \mathrm{dm^3\,mol^{-1}\,s^{-1}}.}
$$
For comparison, the unquenched phosphorescence yield in the unit-triplet-yield approximation is $180/198=0.909$.