Water-cluster distribution with respect to pressure and temperature in the gas phase

Abstract

In spite of decades of extensive studies of water, the experimental information of water clusters larger than the trimer is hardly available yet. To aid the better analysis of certain cluster properties in an experiment, we studied the small-water-cluster distribution (particularly for the minimum-energy structures) in the gas phase. Utilizing the thermodynamic information in the range from the water monomer to the octamer (except for the heptamer) by ab initio calculations, we investigated the mole fractions of the water clusters along the vapor pressure of the condensed phase. These mole fractions increase with increasing temperature or pressure, while the higher clusters increase still more. The entropy increment of the cyclic pentamer relative to the cyclic tetramer is particularly small; thus, the cyclic pentamer shows thermodynamically unusual characteristics. For the trimer, the cyclic structure is more stable than the linear structure at temperatures lower than -400 K, while above this temperature, the latter is more stable due to the entropy effect. Similar phenomena are also expected for the higher clusters. The mole fractions of the higher cyclic clusters are found to be very small in a vapor unless they are uncondensed with insufficient water molecules.PACS number(s): 36.40. +d, 31.20.Ej, 31.20.Tz, 36.90.+f

Water Dimers in the Atmosphere II: Results from the VRT(ASP-W)III Potential Surface

“…However, our more rigorous partition function calculation at 292.4 K yields results of ∆H°) -14.24 kJ/mol, ∆S°) -66.68 J/mol K, and K P (292.4K) ) 0.1151 atm -1 . Thus, slight variations in ∆H°and 47 41 × 10 -3 Suck et al 13 11 × 10 -3 Mhin et al 56 21 × 10 -3 Braun and Leidecker 57 54 × 10 -3 Pfeilsticker et al (292.4 K) 22 18 × 10 -3 ∆S°(ca. 10-15% in this example) can have large ramifications in the approximation used by Pfeilsticker et al due to the exponential dependence of K P (T).…”

What can clusters tell us about the bulk?

“…Therefore we use Eq. (16) and Eq. (17) in an iterative procedure in order to determine the volume V and the particle numbers N ℘ in a self-consistent manner.…”

Structures, binding energies, and spectra of isoenergetic water hexamer clusters: Extensive ab initio studies

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This study is important to understand the hydration structures of cations, anions, electrons, and biomolecules. [19][20][21][22][23][24][25][26] A number of studies have focused their attention on investigating the changes in structural and spectral properties of small water clusters with increasing cluster size, 2,5,8 and also on modeling analytical water potentials to describe accurate properties of the clusters and the bulk. 9,10 Since the water-water intermolecular potential practically governs the structural prediction of the water clusters and the hydrated molecular systems, various ab initio results of the water clusters have been very useful.…”