Sears's itinerant-oscillator model of liquids has been reexamined so as to be consistent with the fluctuationdissipation theorem. An expression for the frequency spectrum of the velocity autocorrelation function is derived which is different from the one given earlier by other authors. Two cases have been considered, one corresponding to the exponential and the other corresponding to the Gaussian correlation in time of the stochastic force. Our calculated spectrum for liquid argon is in very good agreement with the machine computations of Rahman.
tron is little influenced by the pressure whereas the slight decrease of A might be accounted for by the increased hindrance of the rotation of dipoles in the bulk which suppresses the polarity of the solvent.The temperature effect on the spectrum is much more conspicuous as shown in circles of Figure 5.13 The coefficient A decreases rapidly with temperature and at the extreme temperature of 390°it becomes as low as 0.15. Since at this supercritical temperature most of the water molecule may be in the monomeric form and be vigorously agitated,14 the effective potential for the optical electron would not be of a long-range type as shown by Figure 1A or B in the preceding paper and the situation for the electron may be similar to that in paraffins. The decrease of the ground-state energy at higher temperatures is explicable by the temperature dependence of the terms in eq 1; above all, the decrease in (cos 9)av (^µ/3kTR2) and N and the increase in R will be effective for the de-stabilization. It is emphasized that the change of the absorption line shape from symmetric to asymmetric upon the temperature rise is automatically explained by the present theory in terms of the decrease in the value of A which means the gradual change of the major component of the absorption from the ls-2p bound-bound to the bound-free transitions.
Concluding RemarkConsidering that the hydrogenic model is coarse graining in the sense that it ignores the microscopic structure of the solvent, it is gratifying that the model can account for the difference of the solvent molecule to a considerable extent and extract some information proper to the electron in the solvent.
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