Magic number water cluster

Nagashima, U., Shinohara, H., Tanaka, H. (1986). Enhanced stability of ion clathrate structures for magic number water clusters. Journal of Chemical Physics, 84, 209-214. 

Elucidating the origin of magic numbers has been a problem of long-standing interest, made accessible through the use of the laser-based reflectron TOF technique and evaporative ensemble theory. Three test cases are considered, first protonated ammonia clusters where (NH3)4 NHj has been found to be especially prominent, and then two other cases are considered, one involving water cluster ions and another rare gas clusters. 

Figure 28. (a) Mass spectrum of protonated water clusters H+(H20) (n = 4-45) at 119 K and 0.3 torr He in a flow tube reactor. Note the prominence of H3O+(H2O>20 even under quasi-equilibrium conditions, (b) Mass-spectrometric abundance of OH-(H20)n produced under thermal conditions. Note a magic number at n = 20, though not as prominent as for the case of H30+ hydrates. Taken with permission from ref. 92. 

In other related studies,186 we determined the structures of mixed water-methanol clusters the intensity distributions of (H20)n(CH30H)JBH+ showed magic numbers at n + m = 21, 0 < m 8 due to the enhanced stabilities of the dodecahedral cage structures in the mixed clusters. Studies of the metastable dissociation of (H20)B(CH30H)mH+ (n + m < 40) provided evidence that the dissociation channels... 

Water clusters containing simple ions are another area of current experimental and theoretical interest. Accordingly, they are also the subject of EA studies. Chaudhury et al. [113] have used EA methods on empirical potentials to obtain optimized structures of halide ions in water clusters, which they then subjected to AMI calculations for simulation of spectra. EA applications to alkali cations in TIP4P water clusters [114,115] have led to explanations of experimental mass-spectroscopic signatures of these systems, in particular the lack of magic numbers for the sodium case and some of the typical magic numbers of the potassium and cesium cases, and the role of dodecahedral clathrate structures in these species. 

The charge transfer in the first reaction is likely to occur because the ionization potential of water (12.6 eV) is lower than that of nitrogen (15.6 eV). When an APCI-MS system is mn with pure water as mobile phase, a series of protonated water clusters [(HjO) + H] can be observed in the low m/z region with the cluster ion with n=4 being especially abundant due to the magic numbers determining the stability of such clusters (Figure 6.4). If APCI-MS is done in... 

The second factor is the compartmentalization of the reaction medium where each water core is considered as a separate microreactor. The third factor concerns the role of adsorbed species—surfactant, ions, etc.—that could stabilize the colloidal particles at a certain size and prevent them from coagulating [45,46]. The existence of magic numbers was evoked to explain the higher stability of certain clusters [47]. This could be the fourth factor to be considered. 

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