x J. If this energy is converted completely into visible photons (energy-4 X J), the total number of photons is 7 X 10-14/4 X-2 X lo5. Taking account of the light collection efficiency (-0.004), the number of photons collected per diode array channel is-0.8, which could hardly be detected. Considering also the efficiency of energy conversion from discharge to emission, the energy consumed for the excitation of TSE should be several orders of magnitude higher than E estimated above. Namely, most of the electrical energy must be used in the internal discharge across the microcracks. The rise and decay times and pulse width of VTsE exhibit a pulse-to-pulse variation in synchronism with VPyE. The fastest decay time of TSE (-20 p s) is shorter than the normal decay time (-0.7 ms) for PL.I4 These facts indicate that the excited Acknowledgment. One of the authors (H.D.B.

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The self-diffusion coefficient of water is reported to −31°C, where the activation energy reaches 11 kcal/mole compared with 4.5 kcal/mole at 25°C. The similarity of the temperature dependence of the fraction of broken hydrogen bonds, as inferred from Raman and infrared data, and the diffusion coefficient over the entire liquid range forms the basis of empirical support of the dominant role of hydrogen bonding in the fundamental diffusion mechanism.

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The Carr-Purcell spin-echo method has been used to measure the self-diffusion coefficients of the normal paraffins C3Hi2, C«Hi4, C7H16, CsHis, Cí,H2o, Ci0H22, Ci8H38 and C32H66. The measurements were made over a temperature range in order to obtain activation energies. Within experimental error the plots of log D vs. 1 /T are linear. As expected the diffusion coefficients decrease with increasing molecular weight. The activation energies increase with increasing molecular weight. It is proposed that the elementary diffusion process involves the translation of an extended molecule parallel to its chain axis. A reduced temperature plot of the diffusion coefficient clusters the data in an interesting manner and the diffusion coefficients for all the hydrocarbons extrapolated to their respective critical points are approximately equal.

We report solid-state 13C NMR measurements on powder samples of Cw and of a mixture of CM and C^. The NMR resultsshow that, at 296 K, CM molecules rotate rapidly and isotropically in the solid state, while C70 molecules rotate somewhat more anisotropically. These results are consistent with the proposed spherical geometry of CM and prolate spheroidal geometry of C70. The rotational correlation time of CM molecules in the solid state becomes greater than 50 /ts at about 100 K.

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