Accurate determination of the interchain exchange in CsCoCl3 · 2H2O from detailed low-temperature susceptibility data

Detailed measurements of the b and c axis susceptibilities of CsCoCl₃ · 2H₂O have been made between 1.5 and 30 K. The results support the canted antiferromagnetic linear chain model previously used to describe this determine the value of the intrachain exchange. The results give J/k = ?52 ± 2 K and g_b = 4.18 ± 0.08. This value for J/k is significantly larger than what other investigators have reported for CsCoCl₃ · 2H₂O and if the Ising model is applicable it will be more accurate because of the simplicity of the analysis.     

Calculation of the influence of the wind effect and collision-induced velocity changes on the H2O-molecule absorption-line profiles upon broadening by monatomic gases

The influence exerted on the H₂O-molecule absorption line profiles in the H₂O-He, H₂O-Ar, and H₂O-Kr systems by two factors—the dependence of broadening coefficient γ on velocity ν _a of the absorbing H₂O molecule (wind effect) and the collision-induced change in the H₂O molecule velocity—is studied. Three H₂O molecule absorption lines of the ν ₂ band, which are formed by transitions from energy levels with different rotational quantum numbers J and K _a , are chosen for investigations.     

Radiative and radiationless processes of Eu3+ in dimethyl sulfoxide

Solutions of Eu³⁺ in dimethyl sulfoxide (DMSO) exhibit a considerable enhancement in the intensities of bands associated with ?J = 2 both in the absorption and in the emission spectra. This effect is so strong that addition of considerable amounts of either D₂O or H₂O has no effect at all. Contrary to that, addition of very small quantities of DMSO in solutions of Eu³⁺ in D₂O is accompanied by drastic changes in the appropriate transition probabilities. In solutions of Eu³⁺ in DMSO containing relatively small [H₂O] or [D₂O], the primary solvation sphere appears to consist mainly of DMSO. Secondary and primary fluorescence quenching rate constants have been determined such as: k^sec_D2O ? 5.1 M^-1s^-1; k^sec_DMSO ? 20 M^-1s^-1 and k_fl + k^≈_h ? 4.5 × 10²s^-1.     

Adsorption of NO and N2O on Fe-BEA and H-BEA zeolites

FT-IR (Fourier-transform infrared) spectroscopy and density function theory (DFT) methods have been applied to the investigation of the interaction of NO and N₂O with Fe³⁺ species in a beta zeolite (BEA). The geometries for H-BEA and Fe-BEA represented as 10T cluster, and NO and N₂O adsorption on them in η¹-O and η¹-N modes have been completely optimized. The results show that NOx could be adsorbed on Fe³⁺ species and Brønsted acid sites in two modes, but NOx is mainly bonded by N to H or Fe atom and the iron site is preferred. NOx adsorbed on Fe³⁺ species is more stable than on Brønsted acid sites. Adsorption energies for N₂O and NO follow the order of NO > N₂O, predicating that the affinity of NO molecule on BEA zeolite is much stronger than N₂O molecule on BEA zeolite.     

Comparaison de la méthode C.N.D.O. et de modèles analytiques pour la détermination de la polarisabilité de petits amas linéaires

We compare the values of the polarisabilities F(k) of small aggregates obtained by using the C.N.D.O. method to those given by analytical models. The studied clusters are the hypothetical molecules H₇₆ and H₇₈ where the atoms are equally spaced and arranged along a linear closed chain. Our conclusion is that there is a good agreement between C.N.D.O. and RPA results for the absolute value and for the variation with k of F(k). The difference which remains between the 2 curves is mainly due to the neglect of exchange correlations in RPA. This point is checked by taking into account exchange terms in the analytical approach. Moreover we also show that the C.N.D.O. curve presents some specific particularities due to degeneracies in the level spectra. These effects do not alter the forementioned agreement because they are limited to a few values of k (Δk?5) and localized near k = 38 for H₇₆ and k = 0 for H₇₈. In the first case they are due to the spontaneous formation of a charge density wave with wave vector k = 38, in the second case to a depolarization term which would not appear if, for example, the transitions k = 1 and k = ?1 were not exactly degenerated. We extend our analytical study to the n = 1014 case and show how the F(k) values behave when N → ∞.     

Relative intensities in x-ray photoelectron spectra. Part VI. The spectra of He(I), He(II), Y Mζ and Zr Mζ

The 2s- and 2p-electron photoionization cross-sections at photon energies up to 190 eV have been calculated, using the RPAE method for averaged configurations of the C, N, O and Ne atoms. The RPAE method ensures a more accurate relation between the cross-sections, 2s/2p, than that obtained using the Hartree—Fock method. Within the framework of the Gelius—Siegbahn model, but with the use of theoretical atomic cross-sections, we have calculated the photoionization cross-sections for He(I), He(II), Y Mζ, Zr Mζ for CH₄, C₂H₆, C₃H₈, C₂H₄, C₂H₂, NH₃, H₂O, CN^?, N₂, CO, CO₂, N₂O and NO₂^? molecules. For CO, N₂, CO₂, N₂O and H₂O molecules, a comparison is made between the theoretical and experimental cross-sections for hν < 60 eV. The calculated absolute and relative values of the molecular-orbital cross-sections are in reasonable agreement with experiment, especially at hν ? 40 eV. The calculations correctly reproduce the change in intensities under the transition He(I) → He(II). We have shown that our calculations have a significant advantage over those performed using the PW and OPW approximations. It is shown for NO, N₂, CO, H₂O, CH₄, NH₃ and N₂O molecules that the total photoionization cross-section calculated taking into account the real structure of the molecular orbitals is in better agreement with the experimental photoabsorption cross-section than is the sum of the cross-sections for the atoms in a molecule.     

Competition of two mechanisms of retardation of domain walls in the molecular ferrimagnet [Mn{(R/S)-pn}]2[Mn{(R/S-pn}2(H2O)][Cr(CN)6]2

The temperature dependence of the magnetization reversal dynamics of the chiral molecular ferrimagnet [Mn{(R/S)-pn}]₂[Mn{(R/S)-pn}₂(H₂O)][Cr(CN)₆]₂ has been studied at low frequencies of 1–1400 Hz, which are characteristic of the domain wall motion. It has been found from the Cole-Cole plots that domain walls undergo relaxation (at temperatures T > 10 K) and creep (at T < 10 K), and the main parameters determining these modes and the transition between them have been determined. It has been shown that the quantitative regularities of the transition between the modes of the domain wall motion correspond to the concepts of the competition between the contributions of two mechanisms to the domain wall retardation (the periodic Peierls relief and random structural defects).     

Effective dipole moment of rotational transitions of X 2 Y molecules

Contributions determining the rotational dependence of the effective dipole moment of molecules are calculated for the ground state of H₂S and H₂O molecules. The calculation is carried out in various ordering algorithms of perturbation theory. It is shown that the convergence of the effective dipole moment for the ground state of an H₂O molecule in the polynomial representation is rather slow in the rotational operator J _z (the convergence radius is K*≤17). Nonpolynomial forms of the dipole moment as a function of rotational operators are discussed.     

On the additivity of atomic and molecular dipole properties and dispersion energies using H,N, O,H2, N2, O2, NO,N2O,NH3 and H2O as models

The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums S_k , L_k and I_k , and dispersion energy constants C ₆, for H, N, O, H₂, N₂, O₂, NO, N₂O, NH₃ and H₂O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C ₆, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are reliable to within ?20 per cent and the estimates improve substantially as k increases. The effects of molecule formation on DOSDs is examined by comparing the various molecular DOSDs with the sum of the DOSDs for the atoms making up the molecules. Molecule formation results in a net decrease in the amount of dipole oscillator strength for low excitation energies and a compensating net increase for higher energies in a region extending from the absorption threshold to about 100 eV. This is shown to imply that estimates of the stopping average energy I ₀, obtained by using bona fide atomic I ₀ values, are lower bounds to the correct molecular I ₀ results.     

Line phosphorescence spectrum of octachlorodibenzo-p-dioxine at 4.2 K

The line phosphorescence spectrum of octachlorodibenzo-p-dioxine (OCDX) is obtained and interpreted. The symmetry of the lowest triplet state of this molecule is established. The vibrational frequencies found from the vibronic phosphorescence spectrum at 4.2 k are assigned to the vibrational modes of certain symmetry related to individual functional atomic groups of the molecule. The relation between contributions from the spin-orbit (SO) and vibronic-spin-orbit (VSO) interactions to the phosphorescence rate constant k _ph of the OCDX molecule is found from the vibronic line intensities. It is found that the increase in the number of Cl atoms in OCDX compared to that in tetrachlorobenzo-p-dioxine results in the increase in the relative contribution of the VSO interaction to k _ph.     

High sensitivity CW-CRDS of O enriched water near 1.6 μm

The absorption spectrum of ¹⁸O enriched water has been recorded by continuous wave cavity ring down spectroscopy between 5905.7 and 6725.7 cm⁻¹ using a series of fibred DFB lasers. The investigated spectral region corresponds to the important 1.55 μm transparency window of the atmosphere where water absorption is very weak. The typical CRDS sensitivity (noise equivalent absorption of 5×10⁻¹⁰ cm⁻¹) allowed for the detection of lines with intensity as low as 10⁻²⁸ cm/molecule while the minimum intensity value provided by HITRAN in the considered spectral region is 1.7×10⁻²⁴ cm/molecule. The line parameters were retrieved with the help of an interactive least squares multi-lines fitting program assuming a Voigt function as line profile. Overall, 4510 absorption lines belonging to the H₂¹⁸O, H₂¹⁶O, HD¹⁸O, HD¹⁶O and H₂¹⁷O water isotopologues were measured. Their intensities range between 3×10⁻²⁹ and 5×10⁻²³ cm/molecule at 296 K and the typical accuracy on the line positions is 1×10⁻³ cm⁻¹. 2074 of the observed lines attributed to H₂¹⁸O, HD¹⁸O and H₂¹⁷O are reported for the first time. The transitions were assigned on the basis of variational calculations resulting in 288, 135 and 38 newly determined rovibrational energy levels for the H₂¹⁸O, HD¹⁸O and H₂¹⁷O isotopologues, respectively. The new data set includes the band origin of the 4ν₂ bending overtone of H₂¹⁸O at 6110.4239 cm⁻¹ and rovibrational levels corresponding to J and K_a values up to 18 and 12, respectively, for the strongest bands of H₂¹⁸O: 4ν₂, ν₁+2ν₂, 2ν₂+ν₃, 2ν₁, ν₁+ν₃, and ν₂+ν₃. The obtained experimental results have been compared to the spectroscopic parameters provided by the HITRAN database and to the recent IUPAC critical review of the rovibrational spectrum of H₂¹⁸O and H₂¹⁷O as well as to variational calculations. Large discrepancies between the 4ν₂ variationally predicted and experimental intensities have been evidenced for the H₂¹⁸O and H₂¹⁶O molecules.     

Triplet-triplet absorption studies of the intersystem crossing mechanism of 2-aminopurines

The triplet excited states of 2-aminopurine (2-APu) and 2-N, N-dimethylaminopurine (2-DMAPu) in acetonitrile and water have been detected and characterized. Comparison of the initial T-T absorbancies, together with the measured singlet lifetime, in these systems allowed us to determine the relative intersystem crossing rate constants. The ratios k_ISC (2-APu/CH₃CN) : k_ISC (2-APu/H₂O) and k_ISC (2- DMAPu/CH₃CN) were found to be 36.7 and 11.2, respectively. Comparison with the ratios calculated from the luminescence data confirm the previously proposed [1] scheme of electronic levels in these purines.     

Surface and interface optical phonon modes and electron-phonon interaction in a multi-shell spherical system

Within the framework of the dielectric continuum model, interface optical(IO) and surface optical(SO) phonon modes and the Fr?hlich electron-IO (SO) phonon interaction Hamiltonian in a multi-shell spherical system were derived and studied. Numerical calculation on CdS/HgS/H₂O and CdS/HgS/CdS/H₂O spherical systems have been performed. Results reveal that there are two IO modes and one SO mode for the CdS/HgS/H₂O system, one SO mode and four IO modes whose frequencies approach the IO phonon frequencies of the single CdS/HgS heterostructure with the increasing of the quantum number l for CdS/HgS/CdS/H₂O. It also showed that smaller l and SO phonon compared with IO phonon, have more significant contribution to the electron-IO (SO) phonon interaction. Received 16 October 2001 and Received in final form 23 January 2002 Published online 25 June 2002     

Pyrolysis of diethyl carbonate: Shock-tube and flow-reactor measurements and modeling

Shock-tube and flow-reactor experiments were used to study the thermal decomposition of diethyl carbonate (C₂H₅OC(O)OC₂H₅; DEC). The formation of CO₂, C₂H₄, and C₂H₅OH was measured with gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) behind reflected shock waves. The same products were also detected by GC/MS in flow reactor experiments. All experiments combined span a temperature range of 663–1203 K at pressures between 1.0 and 2.0 bar. Time-resolved species concentration profiles from HRR-TOF-MS and product compositions from GC/MS measurements were simulated applying a detailed reaction mechanism for DEC combustion. A master-equation analysis was conducted based on computed energies from G4 calculations. Quantum chemical calculations confirm that DEC primarily decomposes by six-center elimination, C₂H₅OC(O)OC₂H₅ → C₂H₄ + C₂H₅OC(O)OH (1a), followed by rapid decomposition of the alkoxy acid, C₂H₅OC(O)OH → C₂H₅OH + CO₂ (1b). Measured DEC decomposition rate constants k(T) at p ≈ 1.5 bar can be represented by the Arrhenius equation k(T) = 10^13.64±0.12 exp(?204.24±1.95 kJ/mol/RT) s ^{? 1}. Theoretical predictions for k_1a were in good agreement with experimentally derived values. The theoretical analysis also included dipropyl carbonate (C₃H₇OC(O)OC₃H₇; DPC) decomposition and the reactivities of DEC and DPC are compared and discussed in the context of reactivity of dialkyl carbonates under pyrolytic conditions.     

Infrared and raman spectra of barium nitrite monohydrate

The low temperature infrared absorption and room temperature laser Raman spectra of polycrystalline Ba(NO₂)₂ · H₂O and its deuterated analogue are studied. The strongly bonded H-atom of the water molecule makes a highly bent H-bond while the weakly bonded H-atom exhibits a slightly bent (or possible bifurcated) bond consistent with recent structural data; the H-bond enthalpies are estimated to be 3.3 and 2.1 $\text{KCal}\text{mole}$ respectively. The wagging, twisting and rocking modes of the water molecule have been assigned using several well known criteria. The force constants of these modes have also been computed. The librational splittings observed at low temperature are consistent with polarization data, and are being attributed to infrared active factor group components.     

Adsorption of water molecule on (001) and (110) surfaces of MgH2

First principle calculations have been performed to explore the adsorption characteristics of water molecule on (001) and (110) surfaces of magnesium hydride. The stable adsorption configurations of water molecule on the surfaces of MgH₂ were identified by comparing the total energies of different adsorption states. The (110) surface shows a higher reactivity with H₂O molecule owing to the larger adsorption energy than the (001) surface, and the adsorption mechanisms of water molecule on the two surfaces were clarified from electronic structures. For both (001) and (110) surface adsorptions, the O p orbitals overlapped with the Mg s and p orbitals leading to interactions between O and Mg atoms and weakening the O–H bonds in water molecule. Due to the difference of the bonding strength between O and Mg atoms in the (001) and (110) surfaces, the adsorption energies and configurations of water molecule on the two surfaces are significantly different.     

Local mode vibrations of water

Classical trajectory calculations on a realistic potential for the stretching vibrations of the water molecule are used to demonstrate the existence of stable local vibrational modes, which occur in degenerate pairs. The proportion of phase space occupied by such modes increases with increasing energy, with a clearly characterized (0, 2) local state in a local quantum number assignment. It is argued that quantum mechanical corrections will lead to a local mode splitting which is predicted to decrease in magnitude along any given stretching vibrational progression, and to be larger for a given quantum state of D₂O than for H₂O.     

Topological and thermodynamic investigations of ternary mixtures containing cyclic ether: Excess molar enthalpies

Excess molar enthalpies, H_ijk^E, of 1,3-dioxolane or 1,4-dioxane (i) + aniline (j) + benzene or toluene (k) ternary mixtures have been measured as a function of composition at 308.15 K. The H_ijk^E data have been fitted to Redlich-Kister equation to determine ternary adjustable parameters along with their standard deviations. It has been observed that H_ijk^E values predicted by Graph theory compare well with their corresponding experimental values. The observed data have been analyzed in terms of (i) Graph theory (which involves the topology of a molecule); (ii) Prigogine-Flory-Patterson; and (iii) Sanchez and Lacombe theories.     

Vibrational spectra of H2O and CF4 molecules using Lie algebraic approach

In this paper, we introduce one dimensional vibron model to analyze the fundamental, overtone and combination modes of CF₄ molecule and both stretching, bending vibrational mode of bent H₂O molecule up to first overtone with few algebraic parameters. Using the model Hamiltonian, we reported here better results for the vibrational spectra of H₂O. Our analysis suggests some reassignments of levels and predicts location of states in case of CF₄ molecule which was not yet observed.