Term: rotational relaxation time, \(\rho\)
https://doi.org/10.1351/goldbook.RT07475

Definition:
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 @R05411@.

Related Terms:
1) rotational diffusion coefficient (http://doi.org/10.1351/goldbook.R05411).
2) viscosity (http://doi.org/10.1351/goldbook.V06627).
3) debye (http://doi.org/10.1351/goldbook.D01533).

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 416 (https://doi.org/10.1351/pac200779030293)

Citation: 'rotational relaxation time, \(\rho\)' 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

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