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Ab initio surfaces in reduced normal‐coordinate space for water, for the potential energy and components of the dipole moment and second moment of charge about the center of mass, have been refined for use in calculating energies of vibration and expectation values of of these properties in low‐lying states of vibration. The two procedural refinements consist of (i) direct fitting of the surfaces to values obtained at a grid of points, where the internal coordinates for each point have been transformed to reduced normal coordinates by an iterative procedure, and (ii) (small) rotation of the axes into coincidence with a vibrationally invariant set at each asymmetric configuration on the grid. The first refinement brings the calculated values of the constants of anharmonicity xij into much closer agreement with experiment. Both refinements generate significant changes in the fitted property surfaces. For several isotopic species of water calculated expansion coefficients are listed for the potential energy ...

High‐resolution spectra of the infrared‐active stretching fundamental ν3 of 238UF6 have been obtained between 620.6 and 633.5 cm−1 using tunable semiconductor diode lasers. Interference from hot bands was suppressed by cooling the UF6 in a supersonic expansion, and useful monomer concentrations were produced with effective temperatures of

Doppler‐limited tunable diode laser spectra of ν4 of 28SiF4 have been analyzed and the spectroscopic constants determined. In contrast to most earlier low‐resolution studies, the Coriolis constant ζ4, when combined with ζ3 as obtained from previous laser spectroscopy, yields a zeta sum that is within 5% of the expected harmonic value of 1/2. The band origins of 12 overtones and combinations have been obtained from Fourier‐transform spectra (0.04 cm−1 resolution), resulting in estimates of the anharmonicity constants and harmonic frequencies. From the Coriolis constants and the isotope shifts in ν3 we have redetermined the general quadratic force field of SiF4.

The infrared absorption spectrum by the fundamental modes of UF5 is calculated using force constants transferred from UF6 to predict the wavenumbers and using the F atom polar tensor from CH3F to predict the intensities. Calculations are made for several assumed geometrical configurations of UF5. Comparison of the predicted spectra with the recently observed spectrum, in the UF‐stretching region, of a photolysis product of UF6 isolated in an Ar matrix suggests strongly that the structure is square pyramidal (C4v) with the U atom above the F atom equatorial plane. Although the model for the intensities is simple, the calculated spectrum is expected to predict the correct order of magnitude of the intensities of the fundamentals, first overtones, and binary combination bands of UF5, and the approximate wavenumbers for the expected absorption. Some comparisons are given between the calculations for the several structures of UF5 and observed spectra of other XF5 molecules, including PF5, BrF5, and IF5.

Line intensities of the (21 1 0-000) I and (21 1 0-000) III bands of CO 2 have been measured at high resolution and fitted to F -factors of the form F ( m ) = (1 + ξm ) 2 to yield coriolis interaction coefficients, ξ, of 0.14 and 0.33, respectively. Explicit expressions are derived for these coefficients in terms of the molecular parameters and observed and calculated values are compared both for these bands and the previously measured (21 1 0-000) II , (11 1 0-000) I , and (11 1 0-000) II bands. A consistent choice of relative signs of the rotationless dipole moment matrix elements yields agreement within experimental error.

A general expansion is derived for the transition moment between two nondegenerate vibrational states of a polyatomic molecule. This analysis is combined with ab initio surfaces for the potential energy and the dipole moment of water vapor to predict integrated band absorption intensities. Calculations are compared with experiment for several transitions which originate in the zero‐point vibrational state.

The ν3 bands of 187Os16O4, 189Os16O4, and 192Os16O4 have been recorded using both a Michelson interferometer (resolution 0.06 cm−1) and a tunable semiconductor diode laser (resolution limited by the Doppler width, ∼0.0007 cm−1). The rotational fine structure differs from that of most other spherical‐top molecules, for only rotational levels of A symmetry exist. A total of 112 individual vibration–rotation lines in the P and R branches of the three isotopic species were calibrated against stimulated emission lines from a high‐voltage CO2 gain cell, and were used to determine three scalar and two tensor spectroscopic constants for each species; an additional scalar constant was obtained from an analysis of the Q branch of 192OsO4. The strength of P (11) A2 0 was measured for 192OsO4 and yields a vibrational transition moment for ν3 of 0.17±0.02 D. Transitions of all isotopic species that are expected to fall near CO2 laser lines in the region 949–972 cm−1 are tabulated as an aid in the interpreation of satu...

A computer listing of the diagonal F/sup 4/ and F/sup 6/ coefficients of Moret--Bailly (Cah. Phys., 15: 237 (1961)) was prepared for 2