Water dimer equilibrium constant calculation: A quantum formulation including metastable states

Abstract

We present a full quantum evaluation of the water second virial coefficient B(T) based on the Takahashi-Imada second order approximation. As the associated trace T r[e(-βH(AB)) - e(-βH(0)(AB))] is performed in the coordinate representation, it does also include contribution from the whole continuum, i.e., resonances and collision pairs of monomers. This approach is compared to a Path Integral Monte Carlo evaluation of this coefficient by Schenter [J. Chem. Phys. 117, 6573 (2002)] for the TIP4P potential and shown to give extremely close results in the low temperature range (250-450 K) reported. Using a recent ab initio flexible potential for the water dimer, this new formulation leads to very good agreement with experimental values over the whole range of temperatures available. The virial coefficient is then used in the well known relation Kp(T) = -(B(T) - bM)/RT where the excluded volume bM is assimilated to the second virial coefficient of pure water monomer vapor and approximated from the inner repulsive part of the interaction potential. This definition, which renders bM temperature dependent, allows us to retrieve the 38 cm(3) mol(-1) value commonly used, at room temperature. The resulting values for Kp(T) are in agreement with available experimental data obtained from infrared absorption spectra of water vapor.

Hydrogen bond breaking dynamics in the water pentamer: Terahertz VRT spectroscopy of a 20 μm libration

“…[10][11][12] Towards the development of improved water models, VRT experiments on water clusters have been shown to accurately probe the short-range interactions. 13,14 The key distinctions between water clusters and the bulk are the free hydrogens of the clusters. These hydrogens are predicted to have little effect on the librational motions, as evidenced by low resolution spectroscopy studies of small clusters (n = 10-100).…”

Far-infrared VRT spectroscopy of the water dimer: Characterization of the 20 μm out-of-plane librational vibration

“…The study of water clusters with high-resolution spectroscopic methods has facilitated the determination of accurate potential energy surfaces for the water dimer, and more detailed models for bulk water. [1][2][3][4][5][6][7][8][9] A central objective of this research, and one which is actually nearing fruition, is the determination of a "predictive universal water model" capable of describing water in all its forms over wide ranges of conditions, based on the combination of high precision spectroscopic results and state-of-the-art ab initio calculations for small water clusters. 1,6,7,[10][11][12][13][14][15] The most important step in this process is to obtain a "perfect" water dimer potential surface, since two-body forces account for ∼90% of the total cohesive energy of solid and liquid water, 3,6,16 and the dominant many-body interactions (induction) are actually contained in the tensorial description of dimer polarization.…”

Dimerization Degree of Water Molecules, Their Effective Polarizability, and Heat Capacity of Saturated Water Vapor

“…Автори використовують рiзнi методи для дослiдження: 1) визначення концентрацiї ди-мерiв d за допомогою другого вiрiального коефiцi-єнта [10][11][12]; 2) прямий розрахунок [13][14][15], що ви-магає знання коливальних i обертальних спектрiв збуджень димерiв; 3) визначення концентрацiї за допомогою дослiдження теплопровiдностi водяної пари. На жаль, результати суттєво вiдрiзняються один вiд одного.…”

“…Ми розгляне-мо 1) специфiку нормальних координат для диме-ра води; 2) тепловi коливання дипольного момен-ту димера; 3) внесок теплових збуджень у вiль-ну енергiю; 4) узагальнення int ( ) для ансамблю мономерiв та димерiв та 5) їх спiльний вплив на поведiнку ефективної поляризовностi молекули та теплоємностi водяної пари. Ми також детально порiвняємо температурну залежнiсть концентрацiї димерiв, отриману в [10][11][12][13][14].…”