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We present results of gas phase cluster and liquid water simulations from the recently determined VRT(ASP-W)III water dimer potential energy surface (the third fitting of the Anisotropic Site Potential with Woermer dispersion to vibration-rotation-tunnelling data). VRT(ASP-W)III is shown to not only be a model of high 'spectroscopic' accuracy for the water dimer, but also makes accurate predictions of vibrational ground-state properties for clusters up through the hexamer. Results of ambient liquid water simulations from VRT(ASP-W)III are compared with those from ab initio molecular dynamics, other potentials of 'spectroscopic' accuracy and with experiment. The results herein represent the first time to the authors' knowledge that a 'spectroscopic' potential surface is able to correctly model condensed phase properties of water.

We investigated the magnitude and temperature dependence (T dependence) of the dimer absorption in the region of 0–600 cm-1 and the collision-induced absorption (CIA) in the region of 0–1150 cm-1. Together with our previous study of the self water-vapor continuum contributions resulting from far-wing line shapes of the allowed H2O lines in the infrared window between 800 and 1150 cm-1, we find that the three mechanisms have completely different T dependence behaviors. The dimer absorption has the strongest negative T dependence and the continuum absorption from far wings of the allowed lines has a moderately strong negative one. Meanwhile, the CIA exhibits a mild T dependence. In addition, their T dependence patterns are quite different. The T dependence of the far-wing theory varies significantly as the frequency of interest ω varies. For CIA, in general, its T dependence is mildly negative, but becomes slightly positive in the window region between the H2O bands. In contrast, the T dependence of the dimer absorption varies slightly as ω varies. In the microwave and submillimeter region, its T dependence becomes uniform. Concerning the relative importance for each of these three mechanisms, we find that in the infrared widow, the far-wing contributions are the dominant source of the self-continuum. Within the band, its contributions are definitely responsible for the measured continuum data. But, it is impossible to draw quantitatively conclusions on its relative importance unless one is able to improve the accuracy of the local line calculations significantly. On the other hand, within the pure rotational band, the dimer absorptions are a minor contributor to the self-continuum measurements, and its role becomes more important in the microwave and submillimeter regions. Finally, based on our study we conclude that contributions to the self-continuum from CIA in the frequency region of 0–1150 cm-1 are negligible. [ABSTRACT FROM AUTHOR]

We use our adiabatic pseudospectral method (APS) to calculate energy levels of the H2O2 molecule up to 5000 cm-1. Reasonably high accuracy (a few wave numbers) is achieved for a fully six dimensional calculation in a few hours of CPU time on an IBM 580 workstation. This contrasts with previous calculations on the same system which required 50–100 times more computational effort for a similar level of accuracy. The method presented here is both general and robust, and will allow routine studies of six dimensional potential surfaces and the associated spectroscopy, while making calculations on still larger systems feasible. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Precise measurement of all tunneling splittings in the ground vibrational state of the water dimer is essential for a complete and rigorous determination of the intermolecular potential energy surface. Here, accurate experimentally determined rotational constants and tunneling splittings were combined with estimates of the ground state acceptor switching (AS) splittings for both (H2O)2 and (D2O)2 in order to exactly predict the fingerprints of the weakly allowed E2 ↔ E1 transitions and to approximately predict their absolute frequencies. While these transitions are predicted to be quite weak, current technology guided by the now fairly complete water dimer data should permit their observation. The measurement of these weak transitions would permit the direct determination of AS splittings, which has so far eluded experiments. [ABSTRACT FROM AUTHOR]

Extensive new spectroscopic measurements are combined with a global analysis of the ground state data in order to re-examine and to refine the description of the excited vibration rotation tunneling (VRT) states of the water dimer. Notably, six new 'donor torsion' subbands are analytically identified, current vibrational assignments of the Ka = 1 stacks are reassessed, the previously reported (H2O)2 donor torsion overtone (DT)2 and hydrogen bond stretch (S) data sets are augmented, and four new (S) subbands have been measured. Unusually large Coriolis effects are predicted, excited state E2 ↔ E1 assignments are reinforced, and possibilities of experimentally determining ground state AS splitting in (H2O)2 from excited state data are discussed. [ABSTRACT FROM AUTHOR]

Presents research that describes the determination of a polarizable water pair potential by regression analysis of the rotational constants, tunneling splittings, and intermolecular vibrational frequencies. Methods; Results; Conclusions.

Abstract: Attempts of experimental observations of the water dimer spectrum at equilibrium conditions have lasted for more than 40 years since the dimeric hypothesis for extra absorption, but have not yielded any positive confirmed result. In the present paper a new approach is considered: using a high-resolution millimeter-wave spectrum of the water dimer at equilibrium, calculated by a rigorous fully quantum method, we show the potential existence of discernible spectral series of discrete features of the water dimer, which correspond to J+1←J, K lines of E 1 symmetry, already observed in cold molecular beam experiments and having, therefore, well-defined positions. The intensity of spectral series and contrast to the remaining continuum-like spectrum of the dimer are calculated and compared with the monomer absorption. The suitability of two types of microwave spectrometers for observing these series is considered. The collisional line-width of millimeter lines of the dimer at equilibrium is estimated and the width of IR dimer bands is discussed. It is pointed out that the large width of IR dimer bands may pose difficulties for their reliable observation and conclusive separation from the rest of absorption in water vapor. This situation contrasts with the suggested approach of dimer detection in millimeter-waves. [Copyright &y& Elsevier]