High-Accuracy ab Initio Rotation-Vibration Transitions for Water

NASA, Вашингтон, West Virginia, United States
Science (Impact Factor: 33.61). 02/2003; 299(5606):539-42. DOI: 10.1126/science.1079558
Source: PubMed


The spectrum of water vapor is of fundamental importance for a variety of processes, including the absorption and retention of sunlight in Earth's atmosphere. Therefore, there has long been an urgent need for a robust and accurate predictive model for this spectrum. In our work on the high-resolution spectrum of water, we report first-principles calculations that approach experimental accuracy. To achieve this, we performed exceptionally large electronic structure calculations and considered a variety of effects, including quantum electrodynamics, which have routinely been neglected in studies of small many-electron molecules. The high accuracy of the resulting ab initio procedure is demonstrated for the main isotopomers of water.

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Available from: Oleg Polyansky
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    • "The calculations were performed using the MOLPRO electronic structure package [30]. Unlike during generation of our earlier CVRQD surface [7] [8], employing a valence-only treatment at the IC-MRCI level, here all electrons were directly included in the correlation treat- ment. A series of test calculations were performed to study the effect of varying the MRCI reference (complete active) space, which included comparison with small basis (ccpVDZ ) full configuration interaction (FCI) calculations at several geometries, in particular those toward dissociation , and comparisons with a series of single-reference coupled cluster (CC) treatments, up to quadruple excitation (CCSDTQ), at and around equilibrium. "
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    ABSTRACT: A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H216O, the PES has a dissociation energy of D0 = 41109cm−1 and supports 1150 vibrational energy levels up to 41083cm−1. The deviation between the computed and the experimentally measured energy levels is below 15cm−1 for all the states with energies less than 39000cm−1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26500cm−1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.
    Full-text · Article · Jun 2010 · Journal of Quantitative Spectroscopy and Radiative Transfer
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    • "These uncertainties have also limited the fidelity of benchmark line-by-line (LBL) radiative transfer codes. Despite recent advances in ab initio methods [Polyansky et al., 2003], it is still not possible to compute the rotationvibration spectrum of water vapor directly from quantum mechanics. Current information on line properties represents a synthesis of laboratory studies, theoretical calculations, and field observations [Bernath, 2002]. "
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    ABSTRACT: 1] Recent improvements in the spectroscopic data for water vapor have significantly increased the near-infrared absorption in models of the Earth's atmosphere. The climatic effects of increased near-infrared absorption have been simulated with the latest Community Atmosphere Model (CAM3). The shortwave parameterization in CAM3 has been updated to minimize differences between CAM3 and line-by-line (LBL) calculations based upon the High Resolution Transmission (HITRAN) spectroscopic database issued in 2001. The new model reproduces LBL calculations of the near-infrared absorption to within 0.9% ± 1.4% and the near-infrared heating rates to within 0.02 ± 0.02 K d À1 . Estimates of the global annual mean shortwave absorption by water vapor have been calculated from the editions of the AFGL and HITRAN databases issued in 1982 and 2001, respectively. The main changes in water vapor spectroscopy during this period are the addition of many missing weak lines and increased estimates of line strength in near infrared wavelengths. The clear-sky and all-sky shortwave absorption increase by 4.0 W m À2 and 3.1 W m À2 , respectively, in calculations replacing the old with the new spectroscopic parameters. The atmosphere becomes warmer, moister, and more stable with the increased absorption in simulations with sea surface temperatures either prescribed from observations or predicted using a slab-ocean model. The latent heat flux and precipitation both decrease by approximately 2%. Hence the additional absorption has the effect of weakening the hydrological cycle in the atmospheric model.
    Full-text · Article · Sep 2006 · Journal of Geophysical Research Atmospheres
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