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The technique of Brownian dynamics simulation is used to study polarized dynamic light scattering from semi-stiff models of polymers. The primary objective is to determine how sensitive the dynamic scattering form factor, S(q, t), is to dynamic flexibility as opposed to static flexibility (average conformation). S(q, t) over a range of experimentally accessible scattering vector (q) are derived from the dynamical trajectories of many different chains initially selected from an equilibrium ensemble. In order to minimize noise, which is of crucial importance in order to accurately characterize the low amplitude, fast decay components of S(q, t), the center of diffusion or mass is subtracted from the polymer coordinates in most simulations. This procedure, which is valid for systems that have weak coupling between overall translational and rotational motions, has the additional advantage of simplifying S(q, t) since the contribution of overall translation has been factored out. In the analysis of experimental data, premultiplying S(q, t) by exp (+q2 Dt) where D is the translational diffusion constant has the same effect. Simulations are described for dynamically rigid and flexible wormlike chains with variable persistence length (P equals 40 to 100 nm) and contour length corresponding to 762 bp DNA. S(q, t)'s with and without overall translation are analyzed with CONTIN in order to determine lifetime distributions. For large P (> 70 nm), rigid and flexible models are indistinguishable. However, differences are observed when P is less than 70 nm as far as the faster decay components are concerned. The amplitude of the faster decay components are the same for rigid and flexible models but the lifetimes are significantly shorter for the flexible case. For the rigid case, the 'first internal time' corresponds to <(60)-1> where (theta) is the end-over-end rotational diffusion constant. Finally, the simulation results are compared with actual light scattering experiments on 762 bp DNA. A flexible model with P equals 50 nm is in best agreement with experiment. All of the rigid models predict a first internal time that is too long by 40% or more.
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