The elimination of a hydrogen atom in Na(H2O)n

Abstract

By a systematic examination on Na(H2O)n, with n = 4-7, 9, 10, and 15, we demonstrate that a hydrogen loss reaction can be initiated by a single sodium atom with water molecules. This reaction is similar to the well-known size-dependent intracluster hydrogen loss in Mg+(H2O)n, which is isoelectronic to Na(H2O)n. However, with one less charge on Na(H2O)n than that on Mg+(H2O)n, the hydrogen loss for Na(H2O)n is characterized by a higher barrier and a more flexible solvation shell around the metal ion, although the reaction should be accessible, as the lowest barrier is around 8 kcal/mol. Interestingly, the hydroxide ion OH- produced in the process is stabilized by the solvation of H2O molecules and the formation of an ion pair Na+(H2O)4(H2O)n-l-4[OH-(H2O)l]. The activation barrier is reduced as the unpaired electron in Na(H2O)n moves to higher solvation shells with increasing cluster size, and the reaction is not switched off for larger clusters. This is in sharp contrast to the reaction for Mg+(H2O)n, in which the OH- ion is stabilized by direct coordination with Mg2+ and the reaction is switched off for n > 17, as the unpaired electron moved to higher solvation shells. Such a contrast illustrates the important link between microsolvation environment and chemical reactivity in solvation clusters.

Theoretical study of OH-breaking reactions in Na(H2O)n clusters

“…Values of DE h (n), DE a (n) and DE r (n) (kcal/mol) are also given (see text at n = 8. Those numbers are high compared to the approximate barriers found in a previous study ($15(n = 6) and $8(n = 9) kcal/mol) [18]. The DE r (n) values also show a slow reduction with increasing n. The variations of DE a (n) and DE r (n) among the same sizes range over 4-6 and 3-7 kcal/mol, respectively, roughly speaking.…”

“…The approximate activation energy was 11 kcal/mol. Liu's group extended their work to Na(H 2 O) n (n = 4-7, 9, 10 and 15), and found that the H-loss can be initiated by a single Na atom [18]. The barrier was reduced to $8 kcal/mol, since the hydrated electron moved to the outershell with increasing size.…”

A sodium atom in a large water cluster: Electron delocalization and infrared spectra

“…30,31 The time scale of this process, which is characterized also by delocalization and redistribution of the excess electron density, is in a range of hundreds of femtoseconds. To this end, we monitored the positions of both oxygen and hydrogen atoms with respect to sodium along the trajectory.…”

“…24 Size selection was achieved by coupling the UV radiation of a dye laser below the threshold for ionization with the tunable IR radiation from an optical parametric oscillator. [26][27][28][29][30][31][32] The largest size treated was n = 8. 25 A number of theoretical studies addressed sodium-water clusters.…”

A theoretical study of Ti nanoparticle effect on sodium water reaction: Using ab initio calculation

“…When Na and H 2 O meet, an Na/H 2 O interface forms between the different phases. SWR is composed of three steps: hydration, electron solvation, and OH bond breaking (Bewig et al, 1998;Bobbert and Schulz, 2001;Buck and Steinbach, 1998;Chan et al, 2005;Cwiklik et al, 2008a,b;Fukushima et al, 2012;Glendening and Feller, 1995;Hashimoto and Morokuma, 1994;Hashimoto et al, 2013;Kim et al, 2009;Maye and Mezei, 1996;Mundy et al, 2000;Rowley and Roux, 2012;Schulz et al, 2003;Siu and Liu, 2002;Vorontsov and Novakovskaya, 2009;Wheatley, 1996;White et al, 2000). First, water molecules surround the Na atom and solvate its valance electron.…”