Localized states in molecular auger spectra

The influence of the degree of localization of the two final holes on the Auger spectra of a simple diatomic molecule is analysed in detail and cases where such effects may be observed experimentally are discussed. The results are compared with studies of the valence band Auger spectra of solids.     

A new diabatic molecular representation in He+-he charge transfer collision

A “frozen-orbital” diabatic basis has been constructed to study the He⁺-He resonant charge transfer collision in a closecoupled impact parameter treatment. The Σ—Π rotational couplings are reasonably free from the incorrect asymptotic behaviour (α R^?1) Comparison with experiment at large scattering angles demonstrates significant improvement over earlier work.     

Ab initio relativistic self-consistent-field (RSCF) wavefunctions for the diatomics Li2 and Be2

RSCF wavefunctions are calculated using the formalism of the authors. The results essentially agree with the non- relativistic calculations as expected because relativistic effects are negligible for these light atom diatomics.     

A CNDO/2 investigation of the CH3/CF3 substitution effect

The variation of the A-C bond lengths with substitution of methyl by perfluoromethyl in molecules of the kind A(CH₃ )_n is investigated using the CNDO/2 method. Calculations were performed with A as fluorine, oxygen, nitrogen, sulphur and phosphorous and n = 1, 2 or 3. The variation of the A-C bond length can be explained qualitatively by combining two effects, (1) changes in the covalent bond order and (2) changes in the ionic bond strength. While the covalent bond order decreases in all cases, the extent of the decrease depending largely on the electronegativity of A, the ionic bond order increases for fluorine, oxygen, nitrogen and sulphur and decreases in the case of phosphorous. The variations in the ionic bond strength are found to depend on the electronegativity of A as well as on the number of substituted methyl groups.     

Effects of geometric distortions and substituents on rates of intersystem crossing; diazomethane and pyrazoline

We report a qualititive perturbation-theoretic analysis of the effects of substituents on the spin-orbit coupling and on the density of states in diazomethane and pyrazoline systems. The importance of the form of the distortion which accompanies approach to the singlet-triplet crossing zone is also discussed with the aim of determining when reactions involving a spin multiplicity change can compete in rate with spin-conserving reactions.     

Theoretical studies of some nonbenzenoid hydrocarbons—IV : Pleiadiene and related compounds

Pleiadiene and other similar compounds have been studied by the semi-empirical SCFMO method of Pariser, Parr and Pople using the core resonance integral value developed by Lo and Whitehead, Dewar et al. and Yamaguchi et al. It has been found that π^*←π transitions predicted by the methods of Lo and Whiteheadand Dewar et al. suitable for the prediction of ground state properties are also in good agreement with experimental results where available and comparable to those predicted by the method of Yamaguchi et al. developed for the prediction of spectral transitions. The resonance stabilization of the molecules 3,4.5,7,8 and 9 have also been studied. It is found that ethylinic linkage across the naphthalene moity in pleiadiene increases the resonance energy of the final compound, in contrast to our previous observation, i.e. ethylinic linkage across the naphthalene moiety reduces the resonance energy of the final compound.     

Enhanced raman scattering from carbon layers on silver

The broad bands at 1350 and 1550 cm^?1 observed in Raman scattering from Ag in electrochemical cells have been observed on Ag surfaces in tunneling structures and in ultrahigh vacuum. Both the shape and intensity of this scattering is explained by the presence of amorphous carbon on the Ag surfaces.     

The dertermination of trace elements in commerercial human serum albumin solutions by proton-induction x-ray emission spectrometry and neutron activation analysis

Particle-induced x-ray emission (p.i.x.e.) and neutron activation analysis (n.a.a.) are proposed for determining the trace element content of human serum albumin. Application of these methods to some commercial albumin solutions provided concentration data for up to 19 elements, most of which were present at a level below a few μg ml^-1. The precision of the p.i.x.e. technique, as determined by irradiating up to 20 targets from one sample, was about 3% for those elements where counting statistics were good. A comparison between the p.i.x.e. and n.a.a. results showed close agreement, indicating that p.i.x.e. can yield data which are accurate to within 10%. Neutron activation showed very good sensitivity for the elements producing long-lived nuclides (t_{$\text{1}\text{2}$} ? 3 days), but had rather high detection limits for the other elements, unless radiochemical separations were used.     

Excitation profiles of resonance raman spectra in condensed media

A simple model, obtained by reducing a multimode system to a simple coordinate, is proposed to explain the broadening of RRS in liquid or solid media. It is shown that the coherent excitation of the near continuous background of low-frequency modes can cause homogeneous broadening of RRS profiles. The model is applied to the excitation profile of β-carotene.     

The wavefunction of non-stationary states in terms of complex coordinates and a related variational principle

The wavefunction of a decaying state is expressed in terms of complex coordinates as ψ(p) = a(θ)ψ _o(p) + b(θ)x(p), where the square integrable θ_o(p) and x(p) contain the localized and asymptotic information respectively. From Fano theory, we derive the relationship of a(?) and b(?) to the energy and width of the resonance state. This forms the basis for a new variatfonal principle for optimization of trial functions in the complex coordinate—energy plane.     

Phonon spectroscopy of photochemical reactions in organic solids: Photodimerization of 2,6-dimethyl-p-benzoquinone

The Raman phonon spectroscopic study shows that the photodimerization of 2,6-dimethyl-p-benzoquinone. In the solid state is initially a homogeneous reaction but later becomes heterogeneous as the product accumulates. The Ion-temperature electronic absorption spectrum reveals that the reaction is phonon assisted by a polaron formed due to a strong electron- phonon coupling in the cxcited ¹nπ^* state.     

Dispersion energy between closed-shell and half-closed-shell molecules.an ab inito calculation from a perturbation procedure on LiHe

A perturbation procedure previously used for closed-shell molecules is generalized to the case of the interaction between closed-shell and half-closed-shell molecules In particular, the use of different denominators is considered and special attention is paid to the effect of small basis sets for LiHe.     

Conformation-coupled proton migration in tetraphenylporphin

The proton migration process in tetraphenylporphin is found to be strongly coupled to the symmetry-breaking deformation of the porphin skeletal structure. The adiabatic potential for the proton motion suggests that the in-plane N-H bending vibration will make an important contribution to the proton migration.     

Geometry optimised ab inttio calculations on 1,5- and 1,2-dicarba-closo-pentaborane (5)

Geometry optimised ab initio LCAO- MO-SCF calculations for the isomeric carboranes 1,5- and 1,2-dicarba-closo-pentaborane (5) are reported. The optimised geometry of the 1,5-isomer agrees with the experimental geometry and for this isomer greater thermo-dynamic stability is predicted. The framework bonding is due mainly to interactions between the apical atoms and those in the equatorial plane, while within this equatorial plane there is very weak bonding.     

On the barrier to internal rotation in trichloromethyl trichlorogermane,Cl3CGeCl3

Consideration of the continuing successes of the theory of condensed phase isotope effects in the harmonic approximation leads to the conclusion that relative changes expected in anharmonic constants on condensation are constrained to be of the same order of magnitude or smaller than the corresponding changes in harmonic force constants. Benzene-deuterobenzene isotope efforts are analyzed in an illustrative example and a brief discussion of other cases, including CS₂ and CHCl₃, is given.     

Die rotationsisomerie des bicyclopropyls.: II. Die gauche/trans-isomerisierungsenthalpie und-entropie von bicyclopropyl aus ir-intensitäts-messungen. Ein experimenteller test

The determination of the enthalpy ΔH and entropy ΔS of the isomerization bicyclopropy l(trans)? bicyclopropyl(gauche) in the liquid phase by the IR intensity method is described. It is assumed that the ratio of the integral absorption coefficients of the two reference bands at 1351 cm^?1 (gauche) and 1291 cm^?1 (trans), which both belong to the same type of vibration, is temperature independent. The two values ΔH = ?160 ± 40 cal Mol^?1 and ΔS = ?0.4 ± 0.5 cal (Mol · Grad)^?1 respectively. ΔS_U = ?1.8 ± 0.5 cal (Mol · Grad)^?1 thus determined agree well with the corresponding results obtained from NMR and electron diffraction measurements. However, from the pair of reference bands at 695 cm^?1 (gauche) and 1291 cm^?1 (trans), which do not belong to the same type of vibration, strongly differing values for ΔH and ΔSresult under the same assumption as above, which apparently is not applicable in this case.It is shown through these data that the “Fateley-Test” does not provide a suitable tool to decide whether the absorption coefficients of the reference bands are temperature independent or not. The reason for this insignificance is the relatively poor accuracy and reproducibility of measured IR band intensities obtainable up to now.The relative density of bicyclopropyl between ?60°C and + 50°C was determined.     

Inclusion of non-bonded interactions in calculations of vibrational frequencies

The consequences of including non-bonded interactions in the calculation of vibrational frequencies are examined by comparing the results of the consistent force field method (CFF)and a conventional spectroscopic force field calculation method. Sample calculations are given, using ethane as a test case. It is shown that the CFF method is more practical for the calculation of non-bonded interaction parameters for large molecules, provided that the molecular potential energy is first minimized.