On equilibrium structures of the water molecule -: art. no. 214305

被引:148
作者
Császár, AG
Czakó, G
Furtenbacher, T
Tennyson, J
Szalay, V
Shirin, SV
Zobov, NF
Polyansky, OL
机构
[1] Eotvos Lorand Univ, Dept Theoret Chem, H-1518 Budapest, Hungary
[2] UCL, Dept Phys & Astron, London WC1E 6BT, England
[3] Hungarian Acad Sci, Crystal Phys Lab, Res Inst Solid State Phys & Opt, H-1525 Budapest, Hungary
[4] Univ Ulm, Sekt Spektral & Strukturdokumentat, D-89069 Ulm, Germany
[5] Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod 603950, Russia
基金
英国工程与自然科学研究理事会; 匈牙利科学研究基金会;
关键词
D O I
10.1063/1.1924506
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Equilibrium structures are fundamental entities in molecular sciences. They can be inferred from experimental data by complicated inverse procedures which often rely on several assumptions, including the Born-Oppenheimer approximation. Theory provides a direct route to equilibrium geometries. A recent high-quality ab initio semiglobal adiabatic potential-energy surface (PES) of the electronic ground state of water, reported by Polyansky [ ibid. 299, 539 (2003)] and called CVRQD here, is analyzed in this respect. The equilibrium geometries resulting from this direct route are deemed to be of higher accuracy than those that can be determined by analyzing experimental data. Detailed investigation of the effect of the breakdown of the Born-Oppenheimer approximation suggests that the concept of an isotope-independent equilibrium structure holds to about 3x10(-5) A and 0.02 degrees for water. The mass-independent [Born-Oppenheimer (BO)] equilibrium bond length and bond angle on the ground electronic state PES of water is r(e)(BO)=0.957 82 A and theta(BO)(e)=104.48(5)degrees, respectively. The related mass-dependent (adiabatic) equilibrium bond length and bond angle of (H2O)-O-16 is r(e)(ad)=0.957 85 A and theta(ad)(e)=104.50(0)degrees, respectively, while those of (D2O)-O-16 are r(e)(ad)=0.957 83 A and theta(ad)(e)=104.49(0)degrees. Pure ab initio prediction of J=1 and 2 rotational levels on the vibrational ground state by the CVRQD PESs is accurate to better than 0.002 cm(-1) for all isotopologs of water considered. Elaborate adjustment of the CVRQD PESs to reproduce all observed rovibrational transitions to better than 0.05 cm(-1) (or the lower ones to better than 0.0035 cm(-1)) does not result in noticeable changes in the adiabatic equilibrium structure parameters. The expectation values of the ground vibrational state rotational constants of the water isotopologs, computed in the Eckart frame using the CVRQD PESs and atomic masses, deviate from the experimentally measured ones only marginally, especially for A(0) and B-0. The small residual deviations in the effective rotational constants are due to centrifugal distortion, electronic, and non-Born-Oppenheimer effects. The spectroscopic (nonadiabatic) equilibrium structural parameters of (H2O)-O-16, obtained from experimentally determined A(0)(') and B-0(') rotational constants corrected empirically to obtain equilibrium rotational constants, are r(e)(sp)=0.957 77 A and theta(sp)(e)=104.48 degrees. (c) 2005 American Institute of Physics.
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