On the theory for closed shell intermolecular forces

The electron gas model of Gordon and Kim is applied to the interaction of inert gases with a hydrogen molecule. Comparison of the isotropic potential wells with available experimental data shows clearly that modification of the exchange potential along the lines suggested by Rae produces greatly improved agreement when simple power series representations of the dispersion energy are included.     

Spherical tensor theory of long-range intermolecular forces

General expressions are given for the electrostatic, induction and dispersion energies of a pair of interacting, molecules in terms of spherical tensor components of the molecular multipole moments and polarizabilities. The orientation dependence is given in terms of the scalar expansion functions S_l1l2l^k1k2.     

Long range intermolecular forces between conjugated systems

The long range intermolecular forces in terms of the interaction energies between two conjugated molecules are computed and discussed for the cases: (a) a point charge and ethylene, (b) two ethylene molecules, (c) two hexatriene molecules, (d) two benzene molecules, (e) two naphthalene molecules, and (f) two polar merocyanine molecules. The calculations are based on Buckingham's theory of long range intermolecular forces and the author's values for multipole moments and polarizabilities presented previously. The advantage of the treatment is: asymmetric molecules are correctly described and the intermolecular potential is better approximated than by the usual dipole approximation.     

Super-molecule calculations of intermolecular forces between long-chain molecules

Intermolecular interactions between paraffin chains (C₃C₉) in four different mutual orientations have been studied by PCILO and INDO methods. The PCILO method is found to be superior. It is observed that polarity optimization is not required for these interaction studies although it most certainly would be for molecules with more polar bonds. The calculated interaction energies per carbon atom extrapolated to long-chain length are (0.09–0.22) kcal mol^?1 depending upon the orientation and geometry. The effect of a polar head group on the intermolecular interactions of long-chain molecules is also studied using the propionic acid dimer as model. Lone-pair interactions cause one of the dimer orientations to be totally repulsive.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

The excitation of the strontium-like systemS ₀ —P ₁ by the light pulse of duration comparable or larger than relaxation times is considered. The influence of the different pulse envelopes on the time evolution of the density matrix components and on energy spectrum is analyzed. In the case of large detuning and small Rabi frequency the secular approximation is adopted.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

Scattering of a laser pulse on a single atom perturbed by collisions with inert gas atoms is described in terms of suitably defined cross-sections. The relations of the energy balance are explored to show the connection between attenuation and total cross-section for scattering. The different scattering channels, corresponding to the polarisation, spectral decomposition and coherence properties of the light are analysed in terms of the cross-sections. As an example we consider the scattering of a light pulse on an alkali metal atom with a frequency close to the atomic transition frequency from the ground stateS _1/2 to the first excited stateP _1/2.     

Modelling of repulsive potentials from atom charge density distributions: interactions of inert gas atoms

Using electron charge density overlap integrals, a correlation procedure for estimating short-range repulsive intermolecular potentials has been investigated. It is found that the repulsive potentials correlate well with the density overlap integral divided by the square of the distance. A simple combining rule for inert gas atoms is obtained and compared with an accurate determination of repulsive potentials for all the mixed rare gases and with other combining rules.     

Studies of the reactions of lithium atoms with methyl cyanide and methyl isocyanide in inert gas matrices

Linear LiNC is known to be the more stable isomer when isolated in inert gas matrices at low temperatures (4–15K).¹ In an attempt to form the other geometrical isomer, LiCN, studies of the reaction of lithium atoms with CH₃CN and CH₃NC were undertaken. A new absorption in the CN stretching region was observed when lithium atoms were co-condensed with CH₃NC in solid argon and xenon matrices. Photolysis of the matrices with a medium pressure Hg lamp during deposition of Li/CH₃NC seemed to favour the formation of the more stable isomer, LiNC. Reactions of lithium atoms with CH₃CN only led to the formation of LiNC, with or without photolysis.     

Triplet splitting of the 1p state of mercury atoms in inert gas matrices

The effect of O₂ and N₂ impurities on the spectrum of Hg atoms in solid krypton matrices at 20°K has been investigated. The relative intensity of the components of Hg ¹P⁰₁ are shown to depend strongly on the amount of O₂ or N₂ in the matrix. Under certain conditions, the long wavelength triplet component can be completely eliminated. It is shown that the triplet arises from the superposition of spectra of atoms trapped at three distinct trapping sites.     

Vacuum UV emission from reactions of metastable inert gas atoms: Chemiluminescence of ArO and ArCl

Vacuum UV chemiluminescence from bound upper states of ArO, KrO and ArCl is observed from the quenching of excited inert gas atoms by N₂O, O₃, Cl₂ and CCl₄. In these systems, the metastable ³P₂ states of Ar and Kr strongly resemble ground state alkali atoms in their chemical properties.     

Hardness of intermolecular forces and thermal diffusion

An approximate momentum transfer theorem leads to a direct relation between the thermal diffusion ratio and the logarithmic derivative of the potential. The correlation with exact results is excellent.     

On the nature of bonds between carbon atoms

The combined effect of conjugation and van der Waals' interaction has been calculated for carbon sp²-sp² single bonds of different lengths and for different molecular conformations. The bond shortening effect of conjugation is found to be comparable to that of hybridization. The attractive van der Waals' interaction, on the other hand, is always found to be small. It seems thus most improbable that this interaction should be the cause of the planarity of butadiene.     

Higher-order contributions to the intermolecular energy in the perturbation treatment of long-range forces in the light of spherical tensor theory

A preliminary account of the full spherical tensor theory of long-range interactions between two molecules based on a Rayleigh-Schrödinger perturbation treatment is given. The isotropic third-order interaction energy expression is then derived. Finally, the interaction between two tetrahedral molecules in the third-order of perturbation is studied as an example. It is shown that, in some cases, higher-order contributions should be taken into account.     

On the theory of electron correlation in atoms and molecules: Relation between cluster expansion theory and the correlated wave functions method

A relation between the cluster expansion theory of many electron wave functions and the correlated wave functions method is established. In this way, the theoretical basis of the method is elucidated and the approximations involved in its application become apparent. General forms of the correlated wave function, differing in certain important respects from that form usually assumed, are derived.     

On the recombination mechanism of halogen atoms in rare gas diluents

A classical method is developed which explicitly considers the ET and RMC components of the total recombination coefficient and interprets them in terms of contributions from classical similar trajectories (ST). In the case of halogen atoms in rare gases, flash photolysis data can be satisfactorily understood if the depth of the rare-gas—halogen interaction is taken to be of the order of 1 kcal/mole. The results of the ST treatment are found to be in essential agreement with those of Monte Carlo trajectory calculations.