Nonempirical estimation of the ionization conditions of water and amorphous ice

Based on the results of nonempirical dynamics simulations of the vibrationally excited water clusters combined with the data on the dynamic reorganization of water cations obtained upon the vertical ionization of neutral clusters at the additional assumptions about the general rigidity of the hydrogen-bond fragments in amorphous ice and the thermal excitation of rotational vibrations and swinging motions of molecules in liquid water, the characteristic times of structure reorganization are estimated. The possibility to evaluate the photoelectric threshold of amorphous ice from the data about the adiabatic ionization of small water clusters, whose structure reorganization upon the electron removal does not involve opening of rings and formation of chains, is founded. It is shown that the conditions of the threshold ionization of liquid water can be judged from the second intermediate ionization potentials of neutral clusters, that is, from the potentials corresponding to the appearance of cations in which H₃O and OH fragments are separated with one water molecule. Based on an analysis of the electron density distribution in the cationic and neutral water clusters, a functional dependence of the ionization potentials on the number of water molecules is derived. Approximations of the calculated full adiabatic and intermediate ionization potentials of clusters comprising up to 12 water molecules provided the photoelectric threshold estimates of water and amorphous ice in close agreement with experiments.