## rotational diffusion coefficient

https://doi.org/10.1351/goldbook.R05411
Defined by the equation: $D_{\theta }=\frac{t_{\theta }}{\frac{\partial (f(\theta ,\mathit{\Phi }))}{\partial \theta }\ \sin\,\theta }$ where $$f\left(\theta ,\mathit{\Phi }\right)\:\sin \,\theta \ \text{d}\theta \ \text{d}\mathit{\Phi }$$ is the fraction of particles whose axes make an @A00346@ between $$\theta$$ and $$\theta +\mathrm{d}\theta$$ with the direction $$\theta =0$$, and have an azimuth between $$\mathit{\Phi}$$ and $$\mathit{\Phi} + \text{d}\mathit{\Phi}$$; $$t_{\theta }\ \mathrm{d}\mathit{\Phi }$$ is the fraction of particles having an azimuth between $$\mathit{\Phi}$$ and $$\mathit{\Phi} + \text{d}\mathit{\Phi}$$ whose axis passes from values $$<\theta$$ to values $$>\theta$$ in unit time. The axis whose @R05410@ is considered has to be clearly indicated.
Source:
PAC, 1972, 31, 577. (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 617 [Terms] [Paper]