ИСТИНА

The dissolution of an alkaline metal in water is a well-known exothermic process. Many papers are devoted to the investigation of the mechanism of this reaction particularly in the case of sodium. However, its stages are still not clear even when it is metal atoms that interact with water clusters. It is scarcely possible to investigate the process with experimental methods. Therefore, it is nonempirical simulations that can shed light on the mechanism. Judging from the data of molecular-beam experiments [1,2], three sodium atoms are seemingly involved in the sodium hydroxide formation where one of the three acts as a catalyst. A mechanism was proposed [3] that implies the polarization of a sodium dimer in the field of a solvated third sodium atom. However, under experimental conditions, all three atoms should be nearly equivalent and coordinated to the surface of a water cluster. Thus, the motive force of the reaction remains unclear. Excited states of Nax(H2O)y systems should play an important role in the process. Using the high-level multiconfigurational self-consistent field and configuration interaction methods with either singles or singles and doubles, we determined the electronic state spectra of Nax(H2O)y systems (where x = 1 – 4 and y = 0 – 6) and studied the peculiarities of the excited states in detail. Already in the first excited state, the clusters with x = 3 are noticeably polarized, so that one of the sodium atoms has a negative charge. Polarization degree increases with an increase in the excited state number. The spectrum itself becomes more “dense,” and the energy gap between the ground and low-lying excited states rapidly narrows with an increase in the number of either H2O molecules or Na atoms. Thus, it is the electron excitation of the cluster that results in the polarization of the coordinated sodium trimer. One of the atoms acts as a typical catalyst providing the formation of an H2 molecule in its coordination sphere. The process is considered in detail by an example of Na3(H2O)6 cluster where all sodium atoms are originally coordinated to a water trigonal prism.