Rate constants of the O(D) reactions with N2, O2, N2O, and H2O at 295 K

Using a technique of laser flash photolysis coupled with vacuum ultraviolet laser-induced fluorescence spectroscopy, the rate coefficients of O(¹D) reactions with N₂, O₂, N₂O, and H₂O at 295 ± 2 K have been determined to be , k_O2=(4.06±0.24)×10^-11, k_N2O=(1.35±0.08)×10^-10 and . The quoted uncertainties include estimated errors and are the 95% confidence level. The k_N2 and k_N2O values obtained are larger than the current NASA/JPL recommendations by 26% and 16%, respectively, although they are still within the error limits associated with the recommendations.     

Computational study on the kinetics of the reaction between Ca and urea

A computational study, in the framework of statistical kinetic theories, of the reaction of Ca²⁺ with urea has been carried out. The kinetically preferred products are NH₃ + [CaOCNH]²⁺, which are the fifth products in order of stability. The second kinetically preferred products are , followed by [CaNH₃]²⁺+HNCO, whereas the most stable ones, and , appear only in residual quantities. These estimates are in agreement with the experimental evidence and provide a suitable mechanism to understand the competition between Coulomb explosion and neutral loss processes.     

Pulse radiolysis of 9-anthrylmethylammonium cation in aqueous solution

The reaction of hydrated electron with 9-anthrylmethylammonium cation to form the respective anthracene radical anion in aqueous solution has been studied by the method of pulse radiolysis. The rate constant of the reaction of with is reported. It is demonstrated that the anthracene radical anion is unstable and undergoes further reactions. The spectra of transient intermediates, leading to the final reduction products, are presented.     

Linking the loading dependence of the Maxwell–Stefan diffusivity of linear alkanes in zeolites with the thermodynamic correction factor

Molecular dynamics simulations have been carried out to determine the Maxwell–Stefan diffusivity Đ of C1–C4 linear alkanes for a range of molecular loadings, q, in AFI, MOR, MTW, and MFI zeolites. Configurational-Bias Monte Carlo simulations were used to determine the thermodynamic correction factor, Γ ≡ ∂ ln f/∂ ln q. For diffusion in the large 1D pores of AFI, Đ is proportional to 1/Γ. In other zeolite topologies with smaller pore sizes, though such a direct proportionality is not observed, the Đ–q dependence appears to be closely linked to the 1/Γ–q characteristics, especially when the latter exhibits strong inflection.     

Production of HO2 and O2 by multiple ionization in water radiolysis by swift carbon ions

We present a simulation of liquid water radiolysis by swift carbon ions that explicitly takes into account multiple ionization of water molecules. For high linear energy transfer (LET), this process is not negligible with respect to single ionization. The rearrangement of highly ionized water molecules is consistent with production of atomic oxygen. Multiple ionizations is shown to be responsible for creation of a large amount of radicals and O₂ molecules. The simulated yield reproduces very well direct optical measurements for swift ions with comparable LET. Our simulation for is in also agreement with experiment.     

The temperature dependence of the kinetic isotope effect in the reaction of F atoms with CH4 and CD4

The kinetic isotope effect k_F+CH4/k_F+CD4 has been determined by reacting F atoms with mixtures of CH₄ and CD₄, using a discharge-flow-mass spectrometric technique. Experiments were carried out at four temperatures in the temperature range 183–298 K. The Arrhenius expression corresponding to the results is k_F+CH4/k_F+CD4=(0.99±0.02)×exp[(100±5)/T]. The present results are compared with previous published experimental and theoretical results.     

Gas-phase reactivities of charged platinum dimers with ammonia: A combined experimental/theoretical study

Computational and experimental studies of with ammonia are reported. While ammonia is dehydrogenated with either cluster type, the reaction efficiencies are quite different with  = 0.27 for [K. Koszinowski, D. Schröder, H. Schwarz, J. Phys. Chem. A 107 (2003) 4999.] and  = 0.0033 for . DFT-based relativistic calculations are consistent with this distinct behavior, with maximum energies along the reaction path of −13.3 kcal/mol for the cationic and +1.4 kcal/mol for the anionic clusters relative to the reactants. The recently proposed mechanism for the system [D. Xu. X.-Y. Chen, S.-G. Wang, Int, J. Quant. Chem. 107 (2007) 1985.] needs to be modified to account for the experimental findings.     

Laser pulse control of exciton dynamics in the FMO complex: Polarization shaping versus effects of structural and energetic disorder

Femtosecond laser pulse control of exciton dynamics in biological chromophore complexes is studied theoretically using the optimal control theory specified to open quantum systems. Based on the laser pulse induced formation of an excitonic wave packet the possibility to localize excitation energy at a certain chromophore within a photosynthetic antenna system (FMO complex of green bacteria) is investigated both for linearly polarized and polarization shaped pulses. Results are presented for an ensemble of N energetically disordered and randomly oriented FMO complexes. Here, the optimized control pulse represents a compromise with respect to the solution of the control task for any individual complex of the ensemble. For the case of an ensemble with N=10 members the polarization shaped control pulse leads to a higher control yield compared with a linearly polarized pulse. This difference becomes considerably smaller for an ensemble with N=120 members. The respective optimized pulses are used to drive excitation energy in a different ensemble with MN complexes to simulate the usual experimental condition in solution. For the case with N=120, the relative control yield coincides with the resulting control yield “in solution”, giving a slightly higher control yield for polarization shaped pulses.     

On irregular oscillatory structures in resonant vibrational excitation cross-sections in diatomic molecules

We examine in detail the origin of irregular oscillatory structures in the cross-sections of low-energy resonant vibrational excitation of several diatomic molecules by electron impact. We show that these irregularities are caused by a combination of two phenomena: enhancing of the magnitude of the nuclear wave function in the vicinity of poles in the complex energy plane corresponding to quasi-bound vibrational states of the molecular anion, and energy variations of the phase of the nuclear wave function which corresponds to the reflection in the potential well of the molecular anion and which are sometimes called boomerang oscillations. These two phenomena are usually both involved in the nuclear dynamics. The former one is usually dominant at lower energies (NO molecule) and in systems where the potential energy of the molecular anion (H₂ in high rotational states) possesses an outer potential well. The latter one dominates if the width of the quasi-bound vibrational states of the molecular anion is relatively large (e.g. at higher energies for NO and N₂ molecule, H₂ in ground state).     

Coulomb crystals of few particles: Closed-form expressions for equilibrium energies and geometries, and vibrational force constants

Analytical expressions for equilibrium energies and geometries, and the corresponding vibrational force constants are derived for clusters of between three and eight particles interacting through a pairwise potential of the form (r)=(1/3)(r²+2r^-1). In the case of five-, seven-, and eight-particle clusters, these expressions are functions of single parameters that are the larger real roots of respective twelfth-degree polynomials.     

Intercomparison of slip flow velocity measurements of filled polymers by capillary extrusion rheometry

Slip flow can complicate both the measurement of the shear flow behaviour of polymers and the modelling of moulding processes. However, the understanding of the reliability of methods for measuring slip flow behaviour is limited. The results of an intercomparison on the measurement of slip flow behaviour by capillary extrusion rheometry of two polymer melts—a filled high-density polyethylene and a filled ethylene–vinyl acetate copolymer—are reported. Slip velocities were calculated, following the Mooney method, from the dependence of the shear stress–shear rate behaviour on the extrusion die diameter. Both compounds exhibited wall slip: in one case the slip velocity accounted for ≈80% of the total flow rate. Slip velocity results were typically within ≈±20% of the average values for the materials, although scatter up to ≈±40% was obtained for one material at high shear stresses. An analysis of slip velocity measurements indicated that uncertainties of 40–50% are typical (95% confidence level) although significantly higher uncertainties could result if testing conditions (primarily die diameters) are not optimised.     

To what extent are thermodynamic properties of water argon-like?

A new view on the role of H-bonds in water, arising from the principle of corresponding states and Hilbert’s principle is presented. It is shown that the relative values of the H-bond contributions to the fraction volume and the heat of evaporation per molecule do not exceed 5%, although H-bonds are responsible for the non-monotone behavior of the fraction volume. It is established that the average number of H-bonds per molecule everywhere on the vapor–liquid coexistence curve is given by the formula n_H(T) ≈ 4(1 − 0.83t), where and is the critical temperature of water.     

The limiting partial molar volume and apparent molar volume of glycylglycine in aqueous KCl solution at 298.15 and 308.15 K

Apparent molar volumes V_Φ of glycylglycine in aqueous KCl solutions have been obtained from densities at 298.15 and 308.15 K measured with a vibrating-tube densimeter. These data have been used to deduce partial molar volumes of transfer from water to different KCl–water mixtures. values are positive. This result arises from the interaction of KCl with the charged centers of glycylglycine. The results show that depends less on temperature. Hydration numbers are calculated from data and are interpreted in terms of various interactions.     

Electrochemical genosensing properties of gold nanoparticle–carbon nanotube hybrid

We have investigated the electrochemical genosensing properties of gold nanoparticle–carbon nanotube hybrid. Thiolated oligonucleotide probes and mercaptohexanol were self-assembled onto the Au–CNT hybrid. The hybridization events of target oligonucleotides are monitored using electrochemical impedance spectroscopy, cyclic voltammetry and a.c. voltammetry techniques. A redox-active mediator is used to detect the oxidation of guanine residues. The as-fabricated genosensor is able to differentiate between complementary and mismatched hybridizations, relying on the oxidation current of the guanine residues mediated via .     

Receding contact angle in the situation of complete wetting: Experimental check of a model used for evaporating droplets

This paper provides experimental checks of assumptions needed in a model describing the moving contact line of a wetting droplet evaporating in an inert atmosphere. Special interest is given to the maximum extension of the droplet, when the contact line starts receding. The predicted power law dependence between the values of the radius R₀ and the contact angle Θ₀ at the maximum extension is checked against experiments. We find fairly good agreement with theory for very small droplets. However, discrepancies show up rapidly when the droplet size increases.     

Infrared intensities of liquids XXV: Dielectric constants, molar polarizabilities and integrated intensities of liquid toluene at 25 °C between 4800 and 400 cm

The main purpose of this paper is to present accurate infrared integrated intensities of liquid toluene, C₆H₅CH₃, at 25 °C. Also presented are the decadic molar absorption coefficients, E_m, the real and imaginary dielectric constants, ε′ and ε″, and the real and imaginary molar polarizabilities, ^′_m and ^″_m. Integrated intensities were determined as C_j, the area under bands in the spectrum, for all bands between 4800 and 440 cm⁻¹. The contributions from the different bands were separated by fitting the spectrum with classical damped harmonic oscillator bands. The uncertainties in the integrated intensities of most bands are estimated to be 5–10%, with the uncertainties in very weak bands and in shoulders possibly up to 100%. The intensity that should be assigned to the fundamentals is more difficult to estimate due to Fermi resonance with overtone and combination bands, and a best estimate is given. The integrated intensities of the fundamental vibrations and the corresponding transition dipole moments are summarized and are compared with literature values for the gas.     

Mechanism of dissociative excitation of BrCN in electron cyclotron resonance plasma flow of He

The dissociative excitation reaction of BrCN induced by the products of the electron cyclotron resonance (ECR) plasma flow of He was studied based on the electrostatic-probe measurements and on the optical emission spectra of the B²Σ⁺ − X²Σ⁺ transition of CN radicals. The partial pressures of He and BrCN were 3 and 1 mTorr, respectively, and the partial pressure of H₂O, P_H2O, was in the range of 0.0–0.6 mTorr. The electron density, n_e, showed a negative dependence on P_H2O as (2.63 ± 0.13) × 10¹² − (0.23 ± 0.10) × 10¹² m⁻³, and the electron temperature, T_e, a positive dependence, (2.38 ± 0.36) − (4.51 ± 0.15) eV. The CN(B²Σ⁺ − X²Σ⁺) emission intensity showed a negative dependence on P_H2O. Based on a kinetic analysis of these P_H2O dependencies, the decomposition of BrCN does not proceed via electron impact; instead, decomposition proceeds via the processes involving He⁺ and/or He metastable atoms.     

Rare gas–iodine complexes in the ion-pair states

Luminescence and luminescence excitation spectra in the vicinity of the optical–optical double resonance transitions to the I₂(, v_f = 8 and 9, J_f ≈ 55) levels have been measured at the bulb conditions for the I₂ + Rg mixtures (Rg = He, Ar, Xe) at the rare gas pressures 2–20 Torr and room temperature. Luminescence attributed to the RgI₂ complexes in the ion-pair states has been observed for the first time. It is argued that the complexes can be formed by direct optical excitation from the complexes or colliding pairs. Besides, the RgI₂ complexes in the ion-pair states can be formed in nonadiabatic internal conversion processes from the one. The complexes have rather long lifetime, especially in the case of Xe, and decay radiatively and nonradiatively forming I₂ molecules in different ion-pair states.     

Long-term prediction of compressive creep development in expanded polystyrene

The results obtained in investigating the creep of expanded polystyrene (EPS) boards under compressive stress are presented. Power and exponential equations were used for describing creep compliance. It was found that the curves of creep compliance approximated by both equations adequately represent the research results, taking into account the scatter of the experimental data. Based on the calculation and empirical estimate of long-term creep of EPS under compressive stress σ_c=(0.25–0.45)σ_10%, its creep compliance was determined for a period of 10 years in the future. The dependence of on the density of polystyrene boards and the value of long-term compressive stress σ_c was established. The expected values of creep strain development in expanded polystyrene boards EPS 80–EPS 250 under constant compressive stress σ_c=(0.25–0.45)σ_10% are presented for the prediction period of 10 years. To obtain the expected creep values for any other period of time in the interval of 5T50 years, the values of should be multiplied by the empirical coefficient .     

A simple method for predicting the frequency of the infrared inactive carbonyl stretching mode in LM(CO)5 molecules with C4V symmetry

The paper presents a new method for predicting the frequency of the b₁ mode, which is infrared-inactive, in complexes of the type LM(CO)₅ belonging to C_4V point group. The method was based on the relation λ₃=λ₄+[(1−δ/δ)](λ₁−λ₂), where δ=(λ₁−λ₂)/(λ₁−λ₂+λ₃−λ₄), λ₁, λ₂, λ₃ and λ₄ are the λ parameters of the , , b₁ and e modes, respectively. For a large numbers of complexes of the type LM(CO)₅ the average value of δ was found to be 0.80, with a standard deviation of 0.02. With the use of average value of δ, the frequencies of b₁ mode were estimated. The result obtained indicated that there exists a rather good fit between observed and calculated frequencies, with a mean error of 2.7 cm⁻¹. In addition, it was shown that the δ parameter can be used as a criterion of the correct band assignment for the complexes understudy.