The effects of rotation, vibration and isotopic substitution on the electric dipole moment, the magnetizability and the nuclear magnetic shielding of the water molecule

Abstract

Ab initio SCF surfaces for the electric dipole moment, magnetizability and proton and oxygen shielding of the water molecule have been combined with an accurate empirical force field to predict values of these properties for each of the eighteen isotopomers of this asymmetric top molecule in a large number of vibration-rotation states. Results are presented for some of the more important isotopomers in their lower vibration-rotation states.

Zero point corrections to the magnitudes of these properties for H₂ ¹⁶O are 0·4 per cent for the dipole moment, 0·5 per cent for the magnetizability and 2 per cent for the proton shielding. For H₂ ¹⁷O the zero point correction to the oxygen shielding is substantial, 13·1 p.p.m. (4 per cent). Each increment of unity in the rotational quantum number J (at low J) increases the dipole moment by about 0·005 D, has little effect on the magnetizability, decreases the proton shielding by about 0·001 p.p.m. and decreases the oxygen shielding by about 0·04 p.p.m. Vibrational excitation has relatively large effects, about 0·02 D on the dipole moment and several p.p.m. on the ¹⁷O shielding for a single vibrational excitation. Also given are calculated effects of vibration-rotation on the bond lengths and bond angles in HD ¹⁶O and some other isotopomers.