Twolevel systems and lowtemperature glass dynamics: Spectral diffusion and thermal reversibility of hole burning linewidths J. Chem. Phys. 92, 4145 (1990); 10.1063/1.457773Photochemical hole burning of 1,4dihydroxyanthraquinone in polymer glasses: Poly(ethylene), poly(methacrylic acid), and their copolymer systems ~n this ~aper we report an analysis of hole burning line shapes yielding both reversible and lrreVerSl?le contributions to the linewidth which are due to spectral diffusion. These terms show a lInear T dependence and can, through cycling experiments, be investigated in the temperature range of 0.5 < ~ -:: 25 K. The range 1 < T < 25 K is particularly interesting because, under normal condItIons, Debye contributions and local mode contributions overwhelm the small spectral diffusion terms at these temperatures. Comparison between optical data and specific heat data supports our model of spectral diffusion.

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