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A time-resolved powder diffraction study of in situ photodimerization kinetics of 9-methylanthracene using a CCD area detector and parametric Rietveld refinement

Acta Cryst. (2012). B68, 424-430 (

[Plots] Crystal structures of (a) 9-MA monomer and (b) dimer phases. (c) Comparison of the weight fraction progress with time for the monomer and dimer phases in sequential and parametric Rietveld refinements.

A time-resolved X-ray powder diffraction study of 9-methylanthracene (9-MA) during [4π + 4π] photodimerization was performed in situ, which is a typical example of solid-state photoreactions. The study overcomes the drawbacks of photoreaction in single crystals by the application of powder diffraction reaching higher completion (63.8%) of dimer fraction (Figure), and by taking advantage of full quantitative parametric Rietveld refinement of both monomer and dimer phases. The suggested reaction kinetics using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model is a heterogeneous decreasing nucleation and one-dimensional growth.

A. F. Mabied, M. Müller, R. E. Dinnebier, S. Nozawa, M. Hoshino, A. Tomita, T. Sato and S. Adachi