Studies on lanthanoid sulphites: V. thermal decomposition of cerium and neodymium sulphites

The preparation and thermal behaviour of Ce₂(SO₃)₃· 3H₂O, Nd₂(SO₃)₃·6H₂O and Nd₂(SO₃)₃ have been studied. Cerium sulphite undergoes first dehydration which is followed by decomposition to CeO₂ in the temperature range 500 – 850 °C. The decomposition involves two intermediate phases both in air and nitrogen. According to the TG curves the phases in air are Ce₂(SO₃)₂SO₄ and Ce₂SO₃(SO₄)₂. In nitrogen, Ce₂O₂SO₄ was identified and this provides a synthetic route to cerium oxysulphate.Neodymium sulphite decomposes to Nd₂O₂SO₄ when heated in air or in nitrogen up to 950°C. The intermediate levels observed do not correspond to single phases, and the reaction mechanism depends strongly on the experimental conditions.     

Effect of quadratic interactions on the resonance raman scattering of T × t2 jahn-teller systems

Raman excitation profiles and depolarization dispersion curves are calculated for T × t₂ Jahn-Teller systems that are subject to quadratic vibronic (Renner-Teller) coupling as well as frequency changes of the active vibrational mode.     

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.     

Spectroscopy of large molecules in inert gas clusters

Aromatic hydrocarbons provide nucleation centers for the formation of clusters of inert gases in high-flow supersonic beams. Large clusters of Ar, each containing a single tetracene (T) molecule, were prepared by supersonic expansion of the seeded gas at pressures p = 3000–13000 Torr and interrogated by laser-induced fluorescence spectroscopy Evidence is reported for homogeneous line broadening of large TAr_n clusters prepared at p? 8000 Torr.     

Vibrational and high pressure conformational studies of 1,1,2-trichloroethane

The infrared spectra of 1,1,2-trichloroethane were recorded from 4000 to 50 cm^?1 in the vapour and liquid states. Additional spectra above 200 cm^?1 of the low temperature crystal and of two crystalline solids, prepared by compressing the sample in a diamond anvil cell, were obtained. Also, infrared spectra of the liquid and of the compound dissolved in CS₂ were recorded at increased pressures. Raman spectral data of the liquid (including polarization measurements) and of the low temperature crystal were obtained.The fundamental frequencies for each of the two conformers, C₁ and C_s, were assigned and the results checked by normal coordinate analysis. The same diagonal and off-diagonal force constants were employed for the two conformers and the force fields were derived by means of a least squares refinement, including data for chloroethane, 1,1-dichloroethane and various deuterated species. A standard deviation of 3 % was obtained in the final fit.From the changes in relative intensities for infrared bands belonging to the C₁ and C_s conformers with increasing pressure, the volume differences (ΔV¯between the conformers were determined in CS₂ solution and in the pure liquid.     

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.     

Production of the n2 herman infrared system by the energy pooling reaction of N2(Δ3Σ+u) metastable nitrogen molecules

Molecular N₂ emission, observed from an Ar(³Po, 2) and Xe(³P₂) + N₂ flowing afterglow apparatus, indicates that the energy pooling reaction by 2N₂(A ³Σ⁺_u) generates the emission from the Herman infrared system, which is an unassigned nitrogen band system. A lower limit to the formation rate constant for the upper state of the Herman infrared system was found to be 2.5 × 10^-11 cm³ molecule^?1 s^?1. The information presented here may help in the identification of the upper and lower states of the emission system. The 2N₂(A) energy pooling reaction also forms N₂(B³ Π_g, v? 8) but a rate constant cannot be assigned from the present data.     

The orientational correlation parameter g2 of symmetrical benzene derivatives

Values for the orientational correlation parameter of liquid 1,3,5-trifluorobenzene and 1,3,5-trimethylbenzene at 295 K are reported. The results were obtained by combining the Cotton-Mouton constants and the intensity of the reorientational contribution to the depolarized Rayieigh scattering. The g₂ values are compared with the ratio of Rayleigh and single-particle rerorientation times, to which they are related in some models of molecular reorientation.     

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.     

CNDO/2 calculations of rotational barriers in N.N-dimethylamino-azines: Lineshape study of the barrier in 3-dimethylamino-1,2,4-triazine

3-Dimethylamino-1,2,4-triazine has been prepared and the hindered rotation around the exocyclic C-N bond has been studied by a complete lineshape method. CNDO/2 calculations on dimethylamino derivatives of pyridine, pyrimidine, 1,2,4-triazine and 1,3,5-triazine have been performed, and it is found that the calculations satisfactorily reproduce the experimental data. The barrier heights are also discussed in terms of total and π-charge densities obtained from CNDO/2 calculations.     

Reactions of water with carbon and ethylene over illuminated pt/tio2

The room temperature reaction between gas phase water and active carbon to form carbon dioxide and hydrogen on a platinized titanium dioxide catalyst, illuminated with band gap radiation, is reported. Using the same catalyst system, ethylene is converted to ethane, carbon dioxide, hydrogen and a small amount of methane.     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.     

Advantages of deuterium modification of nitroxide spin labels for biological epr studies

The spin label, perdeuterio-N-(1-oxy 1-2,2,6,6-tetramenthyl-4-piperidinyl)maleimide (DMSL) was synthesized and its EPR and saturation transfer EPR spectra were compared to those of the hydrogen analogue, HMSL- The labels were studied as freely tumbling entities and also bound to bovine serum albumin (BSA). Significant gains in spectral resolution and detectability were observed for DMSL relative to HMSL.     

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.     

Vibrational studies in aqueous solutions: Part I. The oxalate ion

The assignment of the fundamental modes and the symmetry of the oxalate ion in solution are re-examined in the light of new experimental evidence. Particular attention is given to the Raman bands at 1455 and 1488 cm^?.     

On the planarity and resonance effect of tetraphenylporphyren and its metallocomplexes

Based on Lennard-Jones potential and resonance effect calculations it has been demonstrated that in solution tetraphenylporphyrin assumes a structure closer to coplanar by 17° from that in the solid state. In the case of metalloporphyrin the tendency towards coplanarity is even greater, about 40°. The minimum in the energy curve is of the same order of magnitude as reported values of free energy of activation for the phenyl rotation.     

Crystalline hydrogen bonded adducts of oxygen bases with peroxybenzoic acids

The preparation and isolation of several crystalline 1 : 1 adducts of substituted peroxybenzoic acids with triphenylphosphine oxide, triphenylarsine oxide, and pyridine oxides, is reported. Infrared spectra indicate the presence of strong intermolecular hydrogen bonds in these adducts.     

Electronic absorption spectroscopy of cooled supersonic expansions: dynamics of the 1B1u state of trans-butadiene

An ultraviolet absorption technique is developed for studying molecules cooled in a supersonic expansion. In this experiment, the temperature-dependent contribution to the diffuseness of electronically excited states is reduced for CS₂ and butadiene. The broadness of the spectral features of the butadiene ¹B_1u state is independent of temperature