Production of electronically excited NF by the reaction of fluorine atoms with HN3

Electronically excited NF in both the a¹Δ and b ¹Σ⁺ states hasbeen observed from the reaction of fluorine atoms with HN₃. The results suggest that fluorine atoms first abstract the hydrogen atom from HN₃, then react with the remaining N₃ to form NF^≠(a¹Δ). NF^*(b¹Σ⁺) is produced by a subsequent energy pooling reaction between NF^≠(a¹Δ) and vibrationally excited HF. The rate of the F + N₃ reaction is estimated to be ≈ 10¹² and ³ mole^?1 s^?1.     

Microscopic-based fluid flow simulation of invasion on a two-dimensional lattice. II. Mobilization and cohesion

An algorithm for modeling secondary invasion processes in porous media is presented. Mobilization of trapped defender fluid is accomplished through interfacial interaction rules. Cohesive forces are also included within the defender phase. A series of simulation runs are performed using two-dimensional lattices and examined to determine optimal conditions for secondary invasions that sweep the trapped defender phase from the porous medium.     

The effect of diatom-diatom collisions on depolarized light scattering linewidths : I. General theory

With the use of an appropriately generalized Waldmann-Snider collision (super-) operator, a unified kinetic theory treatment of depolarized light scattering (both depolarized Rayleigh and rotational Raman) and their related linewidths is presented for gases of rigid rotor molecules. Explicit expressions are given, both exactly and within a distorted wave Born approximation, for the various state-to-state (i.e. rotational quantum number dependent) collision processes which can contribute to any observed linewidths due to diatom-diatom collisions. The results of this paper are employed in the calculation of the depolarized linewidths for the hydrogen isotopes in the following article.     

Collision models for spectral line shapes: explicit parity considerations

The Voigt line shape is standardly used for interpolating between gaussian and lorentzian line shapes as the gas pressure increases. This is equivalent to modelling the collision processes by one relaxation rate. Deviations from the Voigt line shape are obtained by using more detailed forms for the collision model. Here it is shown that parity considerations motivate a class of collision models, and resulting line shapes, that have not been previously considered.     

Visible and near-infrared electronic transitions in NCl and NBr

The reactions of mixtures of halogen atoms (F + (Cl or Br)) with molecular azides produce banded emissions in the visible and near-infrared regions of the spectrum. The observed features correspond to b¹Σ⁺ → X³Σ^? and a¹Δ → X³Σ^? transitions, respectively, in NCl and NBr. The data obtained represent the first spectroscopic observation of the a¹Δ states of these molecules. The molecular constants of the a¹Δ states were determined to have the following values:

     

8.

A lattice model of foam flow in porous media: A percolation approach     

W. G. Laidlaw  W. G. Wilson  Dennis A. Coombe 《Transport in Porous Media》1993,11(2):139-159

Because fluid flow in porous media is opaque to most observational techniques simulations of the processes occurring in porous media have become important. Typical reservoir simulations treat the flow as taking place in some averaged (Darcy-scale) medium but simulations can also be carried out at the level of the network of pores and throats of the porous medium. We report the results of a pore-scale investigation of mechanisms for the alteration of mobility by foam lamella blockage in a network of these spaces and channels of porous media. Saturation and relative permeability curves are obtained using well-known power-law expressions of percolation theory and a rescaling of the percolation parameter readily permits a number of lamella-blocking mechanisms to be treated. An explanation of the shift in breakthrough gas saturation and the deformation of the shape of permeabilityvs saturation curves upon introduction of foam is provided for a variety of blocking mechanisms. The qualitatively different features seen in experimental studies of modification of gas mobility by foam can be rationalized using only two parameters which characterize the throat-size at which blockage commences and the degree of blockage.     

9.

Azide mechanisms for the production of NCl metastables     

A. T. Pritt  R. D. Coombe 《国际化学动力学杂志》1980,12(10):741-753

The production of both the b¹Σ⁺ and a¹Δ states of NCl has been observed from the reaction of HN₃ with flowing streams of Cl and F atoms. The results suggest that a two-step reaction sequence is responsible for the production of excited NCl, as follows: The rate contant (all products) for the first step is k(F + HN₃) > 1 × 10^?11 cm³/molecule sec. Comparison of this value to results obtained in a previous study of the F + HN₃ system yields a value k(F + N₃) = 2 × 10^?12 cm³/molecule sec. The rate constant for the reaction of chlorine atoms with HN₃ was determined to be k(Cl + HN₃) 1 × 10^?12 cm³/molecule sec. The difference between the Cl + HN₃ and F + HN₃ rates is interpreted in terms of an addition–elimination mechanism.     

10.

Yields of singlet nitrenes from halogen atom—azide molecule reactions     

A. T. Pritt  D. Patel  R. D. Coombe 《国际化学动力学杂志》1984,16(8):977-993

Chemiluminescence from the a¹Δ and b¹Σ⁺ excited electronic states of nitrogen halide diatomics is observed when HN₃ is allowed to react with mixtures of halogen atoms in a discharge-flow apparatus. Excited NF (a¹Δ) is produced by the F + HN₃ reaction, and NCl (a¹Δ, b¹Σ⁺) and NBr (a¹Δ, b¹Σ⁺) are produced by the F, Cl, + HN₃ and F, Br + HN₃ reactions, respectively. In the low-density limit, the yield of NF(a¹Δ) was found to be near unity. The yields of the b¹Σ⁺ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N₃ radicals in the flow, support a hypothetical mechanism in which N₃ acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.     

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	NCl	NBr
$\text{ν}{}_{\mathrm{e}}$	9260 ± 10 cm?1	9226 ± 10 cm?1
$\text{ω}{}_{\mathrm{e}}$	904 ± 6 cm?1	763 ± 4 cm?1
$\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}$	4.7 ± 1.2 cm?1	2.4 ± 1.6 cm?1

A lattice model of foam flow in porous media: A percolation approach

Because fluid flow in porous media is opaque to most observational techniques simulations of the processes occurring in porous media have become important. Typical reservoir simulations treat the flow as taking place in some averaged (Darcy-scale) medium but simulations can also be carried out at the level of the network of pores and throats of the porous medium. We report the results of a pore-scale investigation of mechanisms for the alteration of mobility by foam lamella blockage in a network of these spaces and channels of porous media. Saturation and relative permeability curves are obtained using well-known power-law expressions of percolation theory and a rescaling of the percolation parameter readily permits a number of lamella-blocking mechanisms to be treated. An explanation of the shift in breakthrough gas saturation and the deformation of the shape of permeabilityvs saturation curves upon introduction of foam is provided for a variety of blocking mechanisms. The qualitatively different features seen in experimental studies of modification of gas mobility by foam can be rationalized using only two parameters which characterize the throat-size at which blockage commences and the degree of blockage.     

Azide mechanisms for the production of NCl metastables

The production of both the b¹Σ⁺ and a¹Δ states of NCl has been observed from the reaction of HN₃ with flowing streams of Cl and F atoms. The results suggest that a two-step reaction sequence is responsible for the production of excited NCl, as follows: The rate contant (all products) for the first step is k(F + HN₃) > 1 × 10^?11 cm³/molecule sec. Comparison of this value to results obtained in a previous study of the F + HN₃ system yields a value k(F + N₃) = 2 × 10^?12 cm³/molecule sec. The rate constant for the reaction of chlorine atoms with HN₃ was determined to be k(Cl + HN₃) 1 × 10^?12 cm³/molecule sec. The difference between the Cl + HN₃ and F + HN₃ rates is interpreted in terms of an addition–elimination mechanism.     

Yields of singlet nitrenes from halogen atom—azide molecule reactions

Chemiluminescence from the a¹Δ and b¹Σ⁺ excited electronic states of nitrogen halide diatomics is observed when HN₃ is allowed to react with mixtures of halogen atoms in a discharge-flow apparatus. Excited NF (a¹Δ) is produced by the F + HN₃ reaction, and NCl (a¹Δ, b¹Σ⁺) and NBr (a¹Δ, b¹Σ⁺) are produced by the F, Cl, + HN₃ and F, Br + HN₃ reactions, respectively. In the low-density limit, the yield of NF(a¹Δ) was found to be near unity. The yields of the b¹Σ⁺ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N₃ radicals in the flow, support a hypothetical mechanism in which N₃ acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.