rotational relaxation time, ρ 

https://doi.org/10.1351/goldbook.RT07475
Parameter describing the time-dependence of the tumbling of a molecular entity in a medium of viscosity η as originally defined by Debye, and used by Perrin in the original development of the theories of rotational motion of fluorophores.
Note:
Related to the rotational correlation time, τc, by ρ=3τc. Thus, in the case of a spherically emitting species reorienting itself in a homogeneous fluid, ρ=1/(6Dr), with Dr the rotational diffusion coefficient.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 416 [Terms] [Paper]
Citation: 'rotational relaxation time' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.RT07475 RIS BibTex EndNote
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Last revised: February 24, 2014