An investigation of nonequilibrium effects on combustion in supersonic streams
Effects of nonequilibrium free-radical content and composition variation of supersonic streams entering air breathing engines on ignition points and delays
Bryce, C. A.↗
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Electron affinities of the halogen molecules by dissociative electron attachment
Halogen molecules electron affinities by measuring negative ion average translational energy and appearance potentials, noting free radicals heat of formation
Decorpo, J. J.↗
The combustion process
The effect of thermodynamic, chemical, and physical properties on the combustion of materials is discussed. The mechanisms which produce and support combustion of various materials are examined. The effects of free radical reactions, convection and gravitational effects on combustion rates, and changes in flame propagation due to size and shape of surfaces are described.
Downs, W. R.↗
Fracture Behavior in Nylon 6 Fibers
Electron paramagnetic resonance (EPR) techniques are used to determine the number of free radicals produced during deformation leading to fracture of nylon 6 fibers. A reaction rate molecular model is proposed to explain some of the deformation and bond rupture behavior leading to fracture. High-strength polymer fibers are assumed to consist of a sandwich structure of disordered and ordered regions along the fiber axis. In the disordered or critical flaw regions, tie chains connecting the ordered or crystalline block regions are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The effective length distribution was determined by EPR. The probability of bond rupture was assumed to be controlled by reaction-rate theory with a stress-aided activation energy and behavior of various loadings determined by numerical techniques. The model is successfully correlated with experimental stress, strain, and bond rupture results for creep, constant rate loadings, cyclic stress, stress relaxation and step strain tests at room temperature.
Lloyd, B. A.↗
Hydrocarbon polymeric binder for advanced solid propellant
The results of curing vinyl alcohol terpolymers of ethylene, propylene and vinyl acetate are reported for an average functionality of 1.24 when reacted with an equivalent amount of diisocynate, and saturated polyisoprene derivative is described having terminal methyl ester functionality. The development is reported of two hydroxy-telechelic polyisoprenes prepared by DEAB initiated free radical polymerization followed by LiAlH4 reduction of the end groups.
Potts, J. E.↗
Reductive cleavage of the peptide bond
In many biological research efforts, long chain organic molecules are studied by breaking large molecules into smaller components. Cleavage technique of recent interest is the use of solvated electrons. These are formed when aqueous solutions are bombarded with gamma radiation. Solvated electron is very reactive and can reduce most any species present, even to form free radicals.
Holian, J.↗
Chemical evolution of cosmic clouds
Reaction rate characteristics of interstellar matter were studied by the reaction of hydrogen cyanide and molecular hydrogen at about 1000 K at an HCN to H2 ratio of 1 to 100 to simulate the large excess of cosmic hydrogen. It was found that HCN decays with a half life of about 20 hours and that a large surface increases the reaction rate as a function of temperature. Reaction rates may be considerable increased by energetic processes that produce free radicals and ions.
Down, B. D.↗
New horizons in chemical propulsion
After a review of the work of the late-Fifties on free radicals for propulsion, it is concluded that atomic hydrogen would provide a potentially large increase in specific impulse. Work conducted to find an approach for isolating atomic hydrogen is considered. Other possibilities for obtaining propellants of greatly increased capability might be connected with the technology for the generation of activated states of gases, metallic hydrogen, fuels obtained from other planets, and laser transfer of energy.
Cohen, W.↗
Photoionization of atoms and molecules
A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.
Samson, J. A. R.↗
Holographic recording materials - A review
Holographic recording materials in current use are examined along with a few of their applications. Some experimental media are also studied. No effort is made to rank the commercial materials, since satisfactory results can be obtained with any of them. The discussion covers silver halide plates and films, photoresists, thermoplastics, photopolymers, dichromated gelatin, photochromic materials, electrooptical crystals, styryl free radical film, and TEP film. A convenient summation of some material properties is presented in tabular form.
Kurtz, R. L.↗
Interstellar molecules
Progress in the discovery and study of interstellar molecules is summarized. The 36 molecular species thus far identified in interstellar space are listed in several groups which include simple hydrides, oxides, and sulfides, various derivatives of ammonia, molecules involving linear carbon chains, cyanides, and molecules related in structure to formaldehyde, alcohols, or ethers. Several free radicals are described, the discovery of molecules in external galaxies is discussed, and possible mechanisms for molecular formation are noted. Methods for examining relative isotopic abundances by measuring molecules in interstellar clouds are outlined, mechanisms for the excitation of interstellar molecules are reviewed, and values are presented for the C-12/C-13 abundance ratio in a number of interstellar clouds. The detection of interstellar masers is discussed along with pumping mechanisms and masing transitions in H2CO, CH, OH, and SiO. The nature of dense interstellar clouds is examined in terms of several simple and complex cloud models, with emphasis on multiple condensation models.
Townes, C. H.↗
Storage and recombination of atomic H in solid H2
A phenomenological rate process theory is developed for the storage and rapid recombination of atomic hydrogen free radicals in a crystalline molecular hydrogen solid at temperatures in the range of about 0.1-4 K. It is shown that such a theory can account quantitatively for the recently observed dependence of the storage time on the storage temperature, for the maximum concentration of trapped H atoms, and for the time duration of the energy release in the tritium decay experiments of Webeler. The theory predicts that maximum atomic hydrogen concentrations of the order 10 to the 20th per cu cm are realizable for storage temperatures in the vicinity of 0.14 K.
Rosen, G.↗
Silicon monoxide in the 4 micron infrared spectrum of long-period variables
The first-overtone sequence of vibration-rotation transitions of the free radical silicon monoxide are shown to have extreme phase-dependent variations in the spectra of two M-type long-period variables, Omicron Ceti and R Leonis, and the mild S-type long-period variable, Chi Cygni. At maximum light, the SiO band heads are not detectable. Near minimum light, the band heads of (Si-25)O are detected in the 4-micron spectra of all three stars. The band heads of the terrestrially less abundant isotopic species, (Si-29)O and (Si-30)O, are detected in Chi Cygni. Possible explanations of the phase-dependent behavior are discussed, and the role of the stellar chromosphere is considered.
Hinkle, K. H.↗
Upper bound on the equilibrium concentration of atomic H in solid H2
A phenomenological rate process theory has been developed for the production, storage and recombination of atomic H free radicals in a tritium-impregnated solid H2 at temperatures in the range of about 0.1 to 4 K. In this paper it is shown that the theory requires a stringent upper bound on the equilibrium concentration of trapped atomic H, namely that it cannot exceed about 0.125%, even if the temperature is reduced to an arbitrary low value and a very strong magnetic field is applied to the tritium-impregnated H2 solid.
Rosen, G.↗
Energy storage possibilities of atomic hydrogen
The possibility of storing large amounts of energy in a free radical system such as atomic hydrogen is analyzed. Attention is focused on theoretical calculations of the ground state properties of spin-aligned atomic triplet hydrogen, deuterium, and tritium. The solid-liquid phase transition in atomic hydrogen is also examined.
Etters, R. D.↗
The composition of comets
Questions concerning the origin of comets are considered. It is pointed out that the molecular composition of a dense interstellar cloud appears to have exactly the composition needed to produce the observed features of the visible cometary spectrum, which consists mainly of emission bands of unstable free radicals. A working model of cometary structure is discussed together with the classical observations which have led to it. The discussed model was originally described by Whipple (1951). It is emphasized that the model can serve only as a rough guide in efforts to interpret the evolution of cometary behavior. A survey is provided of new techniques which have only recently been applied to cometary observations, taking into account the spectrum of a comet, radio observations, and ultraviolet observations.
Feldman, P. D.↗
Stability of the equilibrium for atomic H in solid H2
The previously reported phenomenological rate process theory for the storage of atomic hydrogen free radicals in a tritium-impregnated crystalline molecular hydrogen solid is used to determine the dynamical stability of the constant uniform equilibrium solution. The analysis indicates that the equilibrium is unstable (thus, unattainable experimentally) for storage temperatures in a certain range (specifically between 0.134 and 0.80 K for 0.03% tritium by weight, and between 0.165 and 0.80 K for 1.20% tritium by weight), while being absolutely stable with respect to arbitrary small-amplitude perturbations for all storage temperatures below and above this range. The theory also predicts the maximum size for a stable H/H2 sample with an appreciable concentration of trapped H and a net excess rate of volumetric heating due to the tritium decay.
Rosen, G.↗
Some speculations about the origin of the high speed HCN jets in Comet Kohoutek /1973f/
The origin of the high-speed HCN jets observed in Comet Kohoutek (1973f) is considered. It is argued that the occurrence of these jets with Doppler shifts corresponding to velocities of approximately 3-5 km/s with respect to the nucleus cannot be explained in terms of either explosive outbursts of trapped sub-surface volatiles, highly exothermic chemical reactions involving free radicals, or the outward expansion of the cometary atmosphere with additional heating. Instead, acceleration of the precursor ions of HCN by energetic electrons in the ionospheric current sheets or current arcs is suggested to play an important role.
Ip, W.-H.↗