Limiting molar conductances (lgr;0) of the Li+and Cs+ions in water have been determined at 0, minus;5, and minus;10thinsp;deg;C as a function of pressure up to 2 kbar. In the studied ranges of pressure and temperature, lgr;0(Li+) increases monotonically with increasing pressure and lgr;0(Cs+) has a maximum against pressure. The lowhyphen;temperature conductances fit well an empirical equation of the critical law form over the pressure range studied; lgr;0=A(T/TSminus;1)ggr;. The parameterTSdecreases with a rise in pressure below 1.5 kbar, but above thatTSis almost constant. The Hubbardndash;Onsager (HO) dielectric friction theory has been critically tested against the experimental results obtained under the extreme conditions after lgr;0are transformed into the drag coefficient (Dgr;zgr;) subtracted by that due to Stokesrsquo; law for perfect slip (4pgr;eegr;R). The observed pressure coefficientdDgr;zgr;/dPis negative for the small ion Li+even in cooled or supercooled water as predicted by the HO theory but positive for the large ion Cs+in contrast to the theoretical prediction. The following three kinds of anomalies in Dgr;zgr;(Cs+) are revealed: Dgr;zgr;0,dDgr;zgr;/dPgsim;0, anddDgr;zgr;/dTgsim;0. The PTC mechanism proposed for explaining the found anomalies has been supported by model calculations; it turns out that the potential for the PTC process can be flat with a reasonable size of cavities.
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