The differential coefficient (∂P/∂n)ne for properties of diatomic molecules and atoms

The coefficient (?P/?n)_ne, where n is the stage of ionization and n_e is the total number of electrons, has been investigated for atoms and for diatomic molecules by the use of tabulated data. The P are (a) orbital configurations, (b) state symbols, (c) ionization potentials, (d) internuclear separations of ground state molecules, (e) crystal radii of ionized atoms, (f) relativistic HF radii of neutral atoms, (g) dissociation potentials of molecules, and (h) the logarithms of the transition moments of electron transitions from the first excited to the ground states of atoms and molecules. The differentials for atoms in cases (a), 0870 0891 V (c) and (h) add to form those for the diatomic molecules, agreeing with a prediction based on the matrix formulation of the periodic system of diatomic molecules diatomic molecules.     

On effective molecular electronic charge densities and vibrational potential energy functions

Empirical relationships connecting equilibrium internuclear distances, harmonic force constants and atomic numbers for diatomic molecules which were presented in a recent communication by Anderson and Parr (Chem. Phys. Lett.10, 293 (1971)) are discussed in detail for 4b-6b and 1a-7b molecules as sample cases. It is shown how to estimate cubic and quartic force constants for these diatomic molecules using these relationships. Methods for estimating stretching force constants in polyatomic and excited state diatomic molecules are presented; sample cases CO₂, CS₂, OCS and the states of CO are treated.     

Nuclear magnetic resonance of K2 in optically pumped potassium vapor

Nuclear spin polarization in diatomic potassium molecules is produced by polarization transfer between dimers and optically pumped potassium atoms. NMR signals from K₂-molecules have been measured. Linewidth studies give information on relaxation processes of nuclear magnetic polarization.     

Calculation of absolute electron-impact ionization cross-sections of dimers and trimers

We report calculations of the electron-impact ionization cross-sections of selected dimers (homonuclear diatomic molecules) and trimers (homonuclear triatomic molecules) using a method which relies only on macroscopic quantities in conjunction with a “defect concept”. The empirically determined defect describes the deviation of the cluster (dimer, trimer) cross-sections from a simple linear dependence on the cluster size. We compare the calculated cross-sections to experimental data for the dimers S₂ and F₂ and the trimer O₃ and we present predictions for the ionization cross-sections of Br₂, I₂, C₂ and C₃ for which no experimental data are available. Lastly, we extend the method to the calculation of ionization cross-sections for the fullerenes C₆₀ and C₇₀. Received 6 December 1999 and Received in final form 10 April 2000     

Resonance dipole-dipole coupling and Fermi resonance in CF4 dimers

The FTIR spectra of Ar(Ne)/CF₄ matrixes have been recorded at matrix concentrations varying in the range 10 000-600 cm⁻¹. The absorptions due to the CF₄ monomers and to the (CF₄)₂ resonance dimers in the spectra of the two matrixes have been identified. The intramolecular Fermi resonance in the spectra of the CF₄ monomers trapped in solid argon and neon has been analyzed. The spectra of the (CF₄)₂ dimers are determined by the strong resonance dipole-dipole interaction of the two interacting molecules and by strengthening or weakening of the intramolecular Fermi resonance interaction.     

Further Dunham energy coefficients of diatomic molecules

Expressions are given for the Dunham energy coefficients Y₃₃ and Y₄₂ in terms of the potential energy coefficients a_i, for diatomic molecules. Their use is briefly discussed.     

The study of ungerade electronic states of the Xe2 molecules in the region of Xe*(5p 56p, 5d, 7s, 6d) by the resonance multiphoton ionization method

Electronic spectra of the Xe2 molecules in the energy range of 77700?C89300 cm^?1 are recorded. The method of resonance enhanced multiphoton ionization of molecules in a supersonic molecular beam was used, in which excitation of the molecules by three photons was followed by ionization caused by a fourth photon (the (3+1) REMPI method). Analysis of the vibrational structure of observed systems of bands yielded information about the dissociation energy and the molecular constants for ungerade states of molecules. On the basis of the Franck-Condon principle, the equilibrium distances for potential curves were estimated from the relative intensities in vibrational progressions. Data on 16 new electronic states of diatomic xenon molecules with the dissociation limits Xe ₂ ^* ?? XE(5p ^{6 1} S ₀) + Xe*(5p ⁵6p,5d, 7s, 7p) were obtained.     

A method for predicting the anharmonicity constants ωeχe of halides of sodium

A method is proposed for estimation of the vibrational anharmonicity constants ω_eχ_e of diatomic molecules. The procedure involves fitting of the potential energy curve obtained by the RKRV method with that obtained by using the 5-parameter Hulburt-Hirschfelder potential function. We have predicted values of ω_eχ_e for alkali halides for which accurate data are not available.     

A periodic table of free diatomic molecules—II predicted internuclear separations from curve-fitted data

Recent theory substantiates the stacking order of the areas in the recently proposed periodic table of the free diatomic molecules. The periodic table suggests curve-fitting algorithms for r_e which, after semi-empirical perturbations yield ground-state values for r_e which agree with literature values and with those from an alternate algorithm to from 5 to 8%. 800 predicted r_e extend to superheavy quasimolecules and to molecules with superheavy atoms, and many pertain to molecules of laser interest.     

X-ray emission spectra of small molecules

An instrument for X-ray emission studies of free molecules is described and electron and fluorescence excitations are discussed. The application of X-ray emission spectroscopy to free molecules is exemplified by the spectra of N₂, CO, NO and CO₂. From the spectra the core level binding energies of the molecules are deduced. For the diatomic molecules vibrational fine structure is resolved and analyzed in terms of different bond lengths in the initial and final states. The change in bond length, when the initial 1s vacancy is formed, is also discussed. The influence of the X-ray selection rules and molecular localization properties on the band intensities are discussed and exemplified by the O1s and C1s spectra of CO and CO₂. In the spectra about ten satellites are found.     

Dissociation energies for the electronic ground states of BeCl,GaH and LiH

The dissociation energies of the diatomic molecules BeCl, GaH and LiH have been computed by fitting empirical potential functions to the true potential energy curves for the electronic ground states of the molecules. The Lippincott three-parameter potential function, the five-parameter Hulburt-Hirschfelder potential function and the Szöke and Baitz electronegativity potential function have been used. The estimated dissociation energiesD ₀ ⁰ are 4·50, 3·09 and 2·94 eV for BeCl, GaH and LiH respectively. These values compare well with the experimental values.     

Quantitative energy level correlations for linear,bent and internally rotating triatomic molecules

This paper is concerned with the study of the quantitative correlation of the rotation-bending energy levels of a linear or bent triatomic molecule with the energy levels of the molecule when there is free internal rotation of a diatomic fragment [as in, for example, Ar(HCl)]. The LiNC and KCN molecules are used as model systems. A correlation parameter γ_r is introduced to quantify the position a molecule occupies in these correlation diagrams; this parameter has the value +1 for an ideal bent molecule, ?1 for an ideal linear molecule, and ?3 for an ideal free internal rotor triatomic molecule. The rotation-bending energy levels of the HCN-HNC isomerization system, and of the double minimum HO₂ system, are also studied.     

Systematics of vibrational intensities for “diatomic” molecules: Approximate formulas

Several approximations are discussed which enable one to estimate electric dipole moment transition matrix elements for diatomic molecules based on a very limited amount of experimental data. For strongly polar molecules, a simplistic point-charge dipole model in which there is no vibrational charge flux predicts a simple relation between the permanent moment, M₀, and its derivative with respect to internuclear separation, M₁. This is found to be approximately valid for a surprisingly large number of polar molecules. Next, approximate matrix elements for the fundamental and overtone bands are presented for a linear dipole moment function. Finally, systematic trends for molecules having similar electronic structures are investigated and combined with the approximations discussed above in order to estimate the transition moments for several molecules of astrophysical interest. An extension to the ν₃ fundamental and overtone bands of CH₄ is suggestive that some of these ideas may be applicable to certain polyatomic molecules as well.     

Raman scattering by zigzag fluoropolymer molecules

The Raman spectra of ultrafine powders consisting of F(CF₂)_nF fluoropolymer zigzag molecules treated as a one-dimensional nanocrystal are investigated. These spectra are compared with the Raman spectra of C_nF_2n+1Br compounds (n=6–10 and 14) and fluoroplastics. It is found that the frequencies of optical vibrations of F(CF₂)_nF fluoropolymer molecules are shifted by more than 10 cm^?1 with respect to the relevant frequencies of C₆F₁₃Br molecules. The length of nanoparticles comprising an organofluoric ultrafine powder is estimated to be L=2–2.5 nm. This estimate is obtained from the measured frequency shifts in terms of the vibrational theory for a crystalline diatomic chain of finite length.     

The periodic table of diatomic molecules—I an algorithm for retrieval and prediction of spectrophysical properties

Related periodicities in properties of diatomic molecules are well known and periodic tables have already been constructed for some classes of molecules. The major difficulty is that two orthogonal periodicities are superposed, at 45° on the Z₁,Z₂ plane, on two others. Our proposed complete table is formed by cutting the plane along the Z₁ and Z₂ directions and stacking areas for similar molecules into 15 blocks. Evidence is presented that 15 is the correct number and that the stacking orders are optimal. It is shown that generalization to ionized molecules requires a fourth dimension, but that this 4-d architecture can be mapped into three dimensions. Computer curve-fitting of data has yielded initial results for r_e in three blocks. 116 data fitted to r_e = A + In √χ (where χ is area number, and A depends on the compartment, in the block) differ from tabulated data by ♂σ ? 3%. 254 predicted r_e are given, some of laser interest, some of superheavy (quasi) molecules, and some for molecules with superheavy atoms.     

Overtone transitions of diatomic dimers XH<Superscript>−</Superscript>-XH<Superscript>−</Superscript> in ionic crystals

The resonance interaction of molecular defects XH^– in ionic crystals is considered. In the dipole approximation, the frequencies and intensities of vibrational transitions of diatomic dimers ^mXH^?-ⁿXH^? are found for the exact (m=n) and quasi-exact (m≠n) resonances. The interaction-atrix elements are obtained with regard to the mechanical anharmonicity in the second order of the theory of perturbation for the case of a linear dependence of the dipole moment of a diatomic molecule on the vibrational coordinate. The expressions obtained are applied to the calculation of overtones in the absorption spectrum of dimers ^mSH^?-ⁿSH^? in a KCl crystal.     

Laser-heating diamond anvil cell studies of simple molecular systems at high pressures and temperatures

We report the application of new laser-heating techniques and sample preparation procedures for simple molecular materials (diatomic molecules and water) under high pressure in the diamond anvil cell (DAC). Both continuous and pulsed laser heating was employed. We probed the materials using Raman spectroscopy and also by analyzing the time evolution of the temperature of the metallic coupler that is used to absorb laser radiation and heat the sample. Raman measurements of H₂, D₂, N₂, H₂O and O₂ show a broadening of intramolecular vibrations at high P−T conditions, indicating a decreasing molecular lifetime, and hence suggest an increasing molecular dissociation. In diatomic molecules the intramolecular bonding can be further probed by observations of sidebands corresponding to vibrational transitions from excited states; the energies of these sidebands imply intramolecular potentials that become increasingly less anharmonic as pressure is increased. We also show that the pulsed heating technique combined with instantaneous radiative temperature measurements provides a useful tool for studies of thermochemical properties and phase transformation boundaries.     

Austauschwechselwirkungen,Intrabandschwingungen und Ti3+-Kristallfeldaufspaltung in dotiertem Al2O3

The absorption spectra of ruby with various Cr concentrations have been studied in the wavelength region between 50 μ and 1 mm at liquid helium and nitrogen temperatures. At liquid helium temperatures two strong absorptions have been found at 37.7 and 106 cm^?1 and weak absorptions at 18.8, 30.7, 33.2 and 43.0 cm^?1. These lines depend on the Cr concentration and vanish at N₂ temperatures. The two strong absorptions have also been observed in Al₂O₃ crystals doped with Ti or V. Sapphire did not show any of these absorptions. The origin of the two strong absorptions in Al₂O₃ crystals doped with Ti, V or Cr are discussed by consideration of magnetic dipole transitions of exchange coupled Cr³⁺ - pairs, the crystal field splitting of Ti³⁺ impurities and impurity — induced lattice modes. The weak absorption lines, on the other hand, may be assigned to transitions between the exchange levels of the second-nearest and fourth-nearest Cr³⁺ pairs if one makes use of the data obtained from the EPR and fluorescence spectra. For the second-nearest Cr³⁺ pairs group theory of the exchange interaction predicts transitions withΔS=2, whereas for the fourth-nearest neighbours no restriction forΔS exists.     

Exact solutions for vibrational levels of the Morse potential via the asymptotic iteration method

Exact solutions for vibrational levels of diatomic molecules via the Morse potential are obtained by means of the asymptotic iteration method. It is shown that the numerical results for the energy eigenvalues of⁷Li₂ are all in excellent agreement with those obtained before. Without any loss of generality, other states and other diatomic molecules could be treated in a similar way.