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Close-coupling calculations with 121 channels at an energy of 155 cm-1 have been made for the rotational scattering of LiF by Ar, using a Lennard-Jones type potential with long range anisotropic terms. Integral cross sections for transitions (jmj )→(j′mj′ ) are given for j = 0, 1, 2, 3, 4 and j′ = 0, 1, 2, 3, 4, 5, and also for the j = 0→8 and j = 0 → 10 transitions. Differential cross sections were obtained for Δj = 1 and j = 0, 1, 2, 3, and for j = 1 →1, 1 →3, 0 →2 and 3 →3 transitions. Rotated scattering amplitudes were used to obtain integral cross sections by numerical integration, but these show little evidence that for Δj ≠ 0 the Δm = 0 transition has a relatively large cross section along an axis perpendicular to the bisector of the angle between the initial and final relative velocity vectors. Certain rules for Δm are suggested, and a comparison with experimental results for (Ar, LiF) and (Ar, CsF) is given.

Close-coupling calculations at 500 cm −1 for the system (Ar,LiH) are used to obtain scattering amplitudes and cross sections for the rotational transitions j = 1 to j' = 0, 2, 3, 4, 5, j = 2 to j' = 3 and j = 3 to j' = 4. The degeneracy-averaged cross sections are in reasonable agreement with experiment for two different simple model potentials. Values for m -dependent cross sections with respect to two frames of reference are compared with various rules for Δ m and with the previous results for (Ar,LiH).

Elastic and inelastic differential cross-sections for the rotational scattering of p-H2 and MuH by He at a single collision energy are calculated with potential surfaces obtained by varying the parameters in a model potential. The importance of the attractive and repulsive terms in the potential, and of the available kinetic energy in the different channels is demonstrated, and it is shown that the whole potential surface determines the scattering cross-sections. Inelastic and elastic scattering are compared, and the differences between the rotational scattering of homonuclear and heteronuclear homopolar molecules are ascribed to the molecular constants rather than to the numbers of open channels.

Extended gaussian basis set ab initio molecular orbital calculations, both with and without configuration interaction, have been made for the polarizability components of CsF, using the distant charge finite field method. Preliminary calculations to obtain a suitable basis were made for the polarizability of LiF and for the dipole and quadrupole moments of LiF, RbF and CsF. A revised value is suggested for the quadrupole moment of RbF. The polarizability anisotropy of CsF is compared with previous empirical values.

To assist the interpretation of polarized rotational scattering experiments from states ( j, m ) to ( j, m' ), differential and total cross sections obtained from close-coupling calculations are given for m values corresponding to j ⩽ 3 in collisions between LiF and Ar at 20 cm −1 . The hypothesis ¦ m ¦-¦ m' ¦= 0 is proposed for the most likely transition, as an extension of the Δ m = 0 rule.

Calculations of the energies for various geometries of Li3, involving linear and perpendicular approaches of a Li atom to a Li2 molecule, are described. The basis set was of double zeta plus polarization contracted gaussian orbitals, and both a single configuration restricted Hartree—Fock function, and a five configuration function were used. The perpendicular approach was found to give the lowest energy, and the most stable form of Li3 is estimated to be about 10 kcal/mole lower in energy than Li + Li2.

Quasi-degenerate many-body perturbation theory with a multi-configuration reference space is used to obtain potential curves for the ground and excited electronic states of Li 2 , LiNa and Na 2 . Correlation contributions are analyzed and the effect of potential curve crossing on laser action is discussed.

Experimental values for 1H and 19F nuclear shielding anisotropies obtained from solid state, nematic phase, and molecular beam measurements are reviewed. Certain discrepancies are pointed out. An anisotropy operator is defined as a sum of two operators corresponding to the Lamb and high frequency terms. Approximations to the high frequency operator are given. Scales of absolute shielding constants are obtained, so that the magnitudes of the anisotropies can be discussed on the basis of non-empirical and semi-empirical calculations, and of the experimental results. The hypothesis due to Ramsey that the potential is constant for a given nucleus in different molecules is used to obtain approximate values for the Lamb term in the nuclear shielding constant. The distinction between shielding in large and small molecules is stressed. For the fluoromethanes and fluorobenzene the results of CNDO/2 molecular orbital calculations are used for a qualitative discussion of the anisotropies.

Data on the diagmagnetic anisotropies of C-C and C-H bonds obtained by measurements of chemical shifts, crystal diamagnetic susceptibilities, and Cotton-Mouton constants are discussed. It is suggested that for both C-C and C-H bonds the absolute value of the transverse susceptibility is greater than the absolute value of the longitudinal susceptibility. A relation for the anisotropy of a straight chain paraffin in terms of the bond anisotropies is derived. It is concluded that the crystal susceptibilities and Cotton-Mouton constants can be explained if the C-H bond anisotropy is greater than about one-half of the C-C bond anisotropy. It is suggested that values for the bond anisotropies obtained from proton chemical shifts are too high, owing to other contributions to the proton shielding, and to the breakdown of the classical magnetic dipole equation. Values for the C-C and C-H bond anisotropies consistent with the available data are given.

The approximate self-consistent molecular orbital method CNDO/2 is applied to calculations on all the valency electrons of some fluorobenzenes and fluoronitrobenzenes. The charge distribution, which shows σ-electron acceptance and π-electron donation by the fluorine atoms, is in accordance with general chemical ideas. It leads to satisfactory values for the dipole moments of the fluorobenzenes and slightly less good values for the fluoronitrobenzenes. The spin densities on the carbon, nitrogen and oxygen atoms obtained for the anions of the fluoronitrobenzenes by the unrestricted form of the method give a satisfactory representation of the experimental hyperfine splitting constants. The elements of the bond order matrix are used with the average energy approximation and theoretical values for r -3 integrals to obtain relative shielding constants for the fluorine nuclei. The assumption made by other workers that the σ-electron terms are effectively constant for the fluorobenzenes is found to be justified. ...

A self-consistent molecular orbital perturbation method suitable for use with the CNDO/2 approximations is formulated. The first-order perturbed equation is solved with an electric field perturbation for several molecules, and the polarizabilities are obtained. The results are too low, particularly for polarizabilities along short molecular axes, with a valency orbital basis set. The inclusion of 2p orbitals on hydrogen atoms gives improved results; but it is concluded that additional basis orbitals on other atoms are required for a valid interpretation of polarizabilities.

In order to assist experimental assignments in olefinic and aromatic fluorine compounds, fluorine nuclear coupling constants have been obtained from the first-order self-consistent perturbation theory equation with the INDO molecular orbital approximation in a series of fluoro-substituted furans. There is a clear distinction between the magnitudes and signs for the four fluorine coupling positions; the importance of the orbital and spin-dipolar contributions is very clear. Tentative signs are suggested for all the coupling constants.

Koopmans' theorem ionization potentials from ab initio gaussian basis set calculations on cis, trans and skew forms of HOOH and HSSH are compared with experimental values from photoelectron spectroscopy.

Ab initio calculations with a double zeta contracted gaussian basis are used to discuss the ionization potentials of o-, m- and p-difluorobenzene, and the correlation with benzene. Interpretations of the experimental X-ray and UV photoelectron spectra are given.

Ionization potentials calculated by the valency electron self-consistent molecular method CNDO/2 for BF 3 , HCHO, O 3 , N 2 , CO, the fluoromethanes, and some fluorobenzenes are compared with experimental values obtained by photo-electron and ultraviolet spectroscopy.

Values of vicinal fluorine nuclear coupling constants for the stable rotamers of (CH2F)2, CHF2, CH2F, (CHF2)2 and CF3. CH2F are obtained from the first-order self-consistent perturbation theory equation with the INDO molecular orbital approximations. A clear distinction is found between gauche and trans values. A comparison with experimental values for similar compounds is made.