Dipole moments, quadrupole moments, dipole polarizabilities and their derivatives are reported for the isoelectronic, isostructural molecules NH,, Hz0 and FH,+ . They were determined by using self-consistent-field wavefunctions and large Gaussian basis sets which included a number of diffuse orbitals. The results for NH? are particularly sensitive to the exponents of the latter.
Recently Swanton et al.
[ 1 ] made a theoretical study of the dipole moment derivatives for the isoelectronic series NH,, H20, and FHZ . In this article we continue their study, at the self-consistent-field level, by looking at the dipole moment, quadrupole moment and dipole polarizability for the same three molecules. Just as their work is relevant to infrared spectroscopy, so is ours to Raman spectroscopy. These three isostructural molecules ( C2"), as well as being candidates for showing isoelectronic trends, are good subjects for exploring the difficulties associated with calculating the dipole polarizability of an anion as opposed to a cation or a neutral species.
In all three cases the z axis was chosen as the C, axis and positive in the direction of the hydrogens (which were placed in the xz plane). The origin was taken to be the centre of mass. For NH, the equilibrium geometry calculated by Bell [ 21 (R= 1.9496 ao, 8 = 102.96' ) was used; for Hz0 the experimental geometry quoted by Ermler and Kern [ 31 was used (R=1.8111 a,, 0=104.45"); and for FH$ the experimental geometry given by Schafer and Saykally [4] was used (R=1.81 ao, 19=114.55"). Calculations were also made at non-equilibrium geometries, as discussed later.
The SCF energies and multipole moments were ' Member of the Ottawa-Carleton Chemistry Institute.