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rotational relaxation time, ρ

Parameter describing the time-dependence of the tumbling of a molecular entity in a medium of viscosityη 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, τ c, by ρ = 3 τ c. Thus, in the case of a spherically emitting species reorienting itself in a homogeneous fluid, ρ = 1 / 6 D r, with D r the rotational diffusion coefficient.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 416
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: https://doi.org/10.1351/goldbook.RT07475.
Original PDF version: http://www.iupac.org/goldbook/RT07475.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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