Molecular beam sampling

Beam attenuation and mass discrimination in effusive and quasieffusive molecular beams of gaseous mixtures have been studied experimentally in an instrument of conventional design, and have been rationalized in terms of transition flow effects and elastic scattering. Their implication in the quantitative monitoring of reacting chemical systems is examined, with particular emphasis in the case of the very-low-pressure pyrolysis technique.     

The pyrolysis of dimethyl sulfide,kinetics and mechanism

The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system at 681–723 K by monitoring total pressure-time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths: with a slow, minor, secondary reaction: In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by with θ = 2.303 RT in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data: which agrees well with the experimental one over the range studied. The reaction is initiated by Me₂S → Me + MeS? and propagated by metathetical radical attack on Me₂S. C₂H₄ is formed by an isomerization reaction which may in part be due to a hot radical: Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.     

The very-low-pressure study of the kinetics and equilibrium: Cl + CH4 ⇄ CH3 + HCl at 298 K. The heat of formation of the CH3 radical

The bimolecular rate constant for the direct reaction of chlorine atoms with methane was measured at 25°C by using the very-low-pressure-pyrolysis technique. The rate constant was found to be In addition, the ratio k₁/k_?1 was observed with about 25% accuracy: K₁₍₂₉₈₎ = 1.3 ± 0.3. This gives a heat of formation of the methyl radical ΔH° _{f 298}(CH₃) = 35.1 ± 0.15 kcal/mol. A bond dissociation energy BDE (CH₃ ? H) = 105.1 ± 0.15 kcal/mol in good agreement with literature values was obtained.     

An eigenfunction solution of entry flow in a semi-infinite pipe at low Reynolds numbers

The developing flow in a semi-infinite pipe is solved for by an eigenfunction method. The results are applicable to zero and low Reynolds number flows. The eigenfunction method yields a solution which accurately predicts overshoots in the axial velocity for small axial positions. Results are presented for both uniform and non-uniform inlet conditions. The latter condition has important implications for numerical simulations of the developing flow problem.This research was performed while Mr Benson was a graduate student at Clarkson College, Potsdam, NY, USA.     

Efficiency and proper efficiency in vector maximization with respect to cones

Vector maximization problems arise when more than one objective function is to be maximized over a given feasibility region. The concepts of efficiency and proper efficiency have played a useful role in the analysis of such problems. Recently these concepts have been extended to vector maximization problems in which the underlying domination cone is a convex cone. In this paper, efficient and properly efficient solutions for the vector maximization problem in which the underlying domination cone is any nontrivial, closed convex cone are examined. Differences between properly and improperly efficient solutions are established. Characterizations of efficient and properly efficient solutions are presented, and conditions under which efficient solutions exist and fail to exist are derived.     

Doubly stochastic matrices over arbitrary vector spaces and the Birkhoff theorem

Doubly stochastic matrices are defined which have entries from an arbitrary vector space V. The extreme points of this convex set of matrices are studied, and convex subsets of V are identified for which these extreme matrices are of a permutation matrix type, i.e. for which a Birkhoff theorem holds.     

Exact transcendental equation for scalar modes of rectangular dielectric waveguides

Conclusion A Fourier operator method has been used to derive for the first time an exact closed-form eigenvalue equation for the scalar mode propagation constants of a buried rectangular dielectric waveguide. The new method has been implemented and the results used to determine the accuracy of the scalar finite-difference approach. It is hoped that the exact results obtained here may assist in the validation of the accuracy of the other numerical and semi-analytical methods.     

The oxidation of HI at low temperatures and the heat of formation of HO2

The kinetics of the oxidation of hydrogen iodide (HI + O₂) at low temperature (414–499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k₁ for the first and rate-determining step (1) These data are combined with an estimated A factor A₁ = 10^9.3±0.2 L/mol·s (assuming a tight linear I···H···O— transition state), to calculate the lower limit of the activation energy for the forward reaction E₁. This leads to a minimum value for the heat of formation of the HO₂ radical, ΔH_f298^°(HO₂) < 3.0 kcal/mol.