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Analysis of conventional ion time-of-Right spectra of N, and CO at laser wavelengths of 248 3nd 305 nm suggests that fragmentation is predominantly chargeasymmetric. In a recent publication we describe the use of covariance mapping to prove that charge-symmetric fragmentation is, in fact, the dominant mechanism at 305 nm. This present contribution shows that the same is true at 248 nm. Moreover, the dissociation energies associated with specific fragmentation channels are the same, within experimental error, for both molecules and at both wavelengths.

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We solve exactly the one-dimensional random field Ising model for two classes of magnetic field distributions: symmetric exponential (model I) and non-symmetric exponential (model 11). For both models, expressions for the free energy at all finite temperatures are presented. The low-temperature region is examined in more detail; we obtain the zero-temperature energy and entropy in closed form; it is shown that the free energy of both models has an expansion in integer powers of temperature. Model I has a non-vanishing zero-point entropy for all values of the parameters as soon as randomness is diluted. In model I1 the zero-point entropy is zero except for a discrete sequence of values of one parameter. In some cases the zero-temperature magnetisation is positive whereas the average magnetic field is negative; the magnetisation may also change sign as a function of temperature.