Ortho-para Hydrogen Conversion Research Articles

Activated Adsorption of Hydrogens on Aromatic—Alkali-Metal Charge-Transfer Complexes

The ortho—parahydrogen-conversion reaction (p-H2⇌o-H2) and the hydrogen—deuterium exchange reaction (H2+D2⇌2 HD) were used to investigate the activated adsorption of hydrogen on aromatic—alkali-metal charge-transfer complexes. When deuterium gas was introduced onto these complexes, it was found that hydrogen exchange takes place between deuterium and the complexes (denoted as H2⇌D2). The kinetics of the parahydrogen conversion and of the H2—D2 exchange were studied as a function of the temperature and it was found that the rate of reactions was first order at a constant pressure. On the basis of the effect of the temperature on the rate constant, an apparent activation energy E for p-H2⇌o-H2 was 4.4 kcal/mole in the presence of phthalonitrile—Na (I), 3.7 kcal/mole with tetracyanopyrene—Cs (II), 10.0 kcal/mole with violanthrene B–Cs (III) and 0.6 kcal/mole with graphite—Cs (IV). Further, E for H2+D2⇌2 HD was 6.6 kcal/mole in the presence of (I) and ∼0.6 kcal/mole with (IV). These reaction suggests that the strong activated adsorption of hydrogen on the complexes takes place with the excess charge transferred from alkali metal to the organic molecule. Further, it was found that the hydrogen exchange reaction between gaseous hydrogen and phthalonitrile takes place reversibly.

Paramagnetic Catalysis of the Ortho—Parahydrogen Conversion

A theory is presented for the paramagnetic catalysis of ortho—para transitions in molecular hydrogen, deuterium, and tritium. The cause for reaction is taken to be an inhomogeneous magnetic field, orginating from a catalyst molecule and operative during the binary collisions of catalyst and reactant species. Formulas for the distorted wave approximation to the cross sections are presented, as are expressions for the specific rates of the associated thermal reactions. Exploratory calculations are performed for the oxygen catalyzed para (L=0)→ortho(L=1) transition in hydrogen. With the assumption of a hard-sphere interaction the rates calculated for 77.3° and for 86°K turn out to be only about 25% to 30% of the experimentally observed rates.

Low-temperature ortho-para conversion of hydrogen on silver

A study of the low temperature ortho-para conversion of hydrogen on sintered silver particles was carried out to probe the surface for paramagnetic chemisorbed species. No paramagnetic structure of chemisorbed oxygen was found. Hydrogen chemisorbs on silver below room temperature only in the presence of adsorbed oxygen. No paramagnetic surface structure results. On the other hand, hydrogen chemisorbed at high temperatures gives a strongly paramagnetic surface; it appears to be chemisorbed in atomic form at centres containing firmly bound residual oxygen atoms and is not easily removed. This may explain the reported existence of a strongly bound paramagnetic form of oxygen and generally must be considered in adsorption studies on “bare” surfaces produced by hydrogen reduction.

On the catalytic activity of certain synthetic organic polymers

1. Data were obtained on the catalytic activity of synthetic polymers with conjugated bondspolymethyl vinyl ketone and polyparadiethynylbenzene in reactions of ortho-para and para-ortho conversion of hydrogen and isotopic exchange of hydrogen with deuterium. 2. The indicated polymers manifest catalytic activity in the reaction of para-ortho conversion of hydrogen at high temperatures and in the reaction of ortho-para conversion of hydrogen at the temperature of liquid nitrogen. The kinetic principles correspond to a first-order reaction rate equation (according to the change in pressure). The reaction of isotopic exchange of hydrogen with deuterium practically does not occur in the presence of these polymers. 3. A comparison of the results obtained with the physical properties of the polymers shows that the reaction of para-ortho conversion evidently proceeds according to a unique physical mechanism, on account of the influence of the surface paramagnetic centers, the appearance of which is related to the presence of complexes with charge transfer.

13. Reactivity of carbon surfaces studied by low temperature orthopara hydrogen conversion

13. Reactivity of carbon surfaces studied by low temperature orthopara hydrogen conversion

A liquefier for producing para-hydrogen and catalysts for the ortho-para conversion of hydrogen

A liquefier for producing para-hydrogen and catalysts for the ortho-para conversion of hydrogen

Nuclear Spin Conservation in Ortho-Para Hydrogen Conversion

The details of statistics of the nuclear spin states in the ortho-para hydrogen conversion by hydrogen atoms are considered. It is shown that the observed rate of conversion is 5/6 the rate of formation of the transition state if H3 is linear. The factor is 8/9 is H3 if an equilateral triangle.

ELECTRON SPIN RESONANCE ABSORPTION OF DIPHENYLPICRYLHYDRAZYL–ZINC OXIDE MIXTURES

Electron spin resonance measurements on mixtures of αα-diphenyl-β-picrylhydrazyl (DPPH) and zinc oxide when compared with corresponding determinations on DPPH itself, and with DPPH–potassium chloride mixtures, indicate that there is a transfer of electrons between the DPPH and the zinc oxide. These observations support earlier published views of Harrison and McDowell, who found that the above mixture was able to enhance the catalysis of the ortho–para hydrogen conversion, and the hydrogen–deuterium exchange reaction.

Catalytic Activity of a Graded Set of Charcoals for the Hydrogen-Deuterium Equilibration and the ortho-para Hydrogen Conversion and Electron Spin Resonance

Catalytic Activity of a Graded Set of Charcoals for the Hydrogen-Deuterium Equilibration and the ortho-para Hydrogen Conversion and Electron Spin Resonance

The Rate of Evaporation of Liquid Hydrogen Due to the Ortho-Para Hydrogen Conversion

The evaporation of liquid hydrogen caused by the heat of reaction of the ortho-para conversion has been measured as a function of the o-hydrogen concentration. The results are discussed, and a set of curves is given which describes all cases of practical interest. Methods of minimizing the rather serious evaporation of liquid hydrogen as the result of this effect are suggested.

Organic Bond Strengths and the Heat of Vaporization of Carbon

KINETIC studies on several independent chemical reactions have led to a value of about 104 kcal. for the heat X of removal of the first hydrogen from methane. Thus Trenner, Morikawa and H. S. Taylor1obtained 108 ± 5 kcal. from the reaction of deuterium atoms with methane, Patat2 a value of about 103 kcal. from the ortho-para hydrogen conversion by methyl radicals, and Rice and Dooley3 a value 100 ± 6 kcal. from the thermal decomposition of methane at high temperatures. Butler and Polanyi4 have measured the velocity of the homogeneous thermal decomposition of alkyl iodides at low pressures, and their results, together with some thermo-chemical data, lead to the value X = 103.65.

Solid Free Radical as Catalyst for Ortho—Para Hydrogen Conversion1a

Solid Free Radical as Catalyst for Ortho—Para Hydrogen Conversion^1a

On the ortho-para conversion of hydrogen in diamagnetic liquids

The first page of this article is displayed as the abstract.

The Theoretical Treatment of Chemical Reactions Produced by Ionization Processes Part I. The Ortho-Para Hydrogen Conversion by Alpha-Particles

The possible individual processes that may occur in a gaseous system under irradiation from alpha-particles have been examined from the theoretical standpoint. The ionization, clustering and the fate of the ions have been studied. The ortho-para hydrogen conversion under the influence of alpha-particles has been chosen as an example with which to illustrate the method of treatment. Recent experimental data by Capron have been analyzed to confirm his conclusion that atomic hydrogen is responsible for the large ratio of molecules converted to ions produced (M/N = (700 to 1000)/1). It is also shown that clustering is unimportant in this case and that the paramagnetism of the ions is of negligible importance in producing the spin-isomerization. The role of mercury atoms in removing atomic hydrogen from the system is found to be negligible. Removal of atoms by three body collision of two atoms with molecular hydrogen is slow compared with removal at the walls of the reaction vessel. Analysis of this latter process shows excellent agreement with the experimental data on the conversion efficiency of the system.

The Use of the Ortho—Para Hydrogen Conversion in the Detection of Free Radicals Produced in Photo-dissociation1

The Use of the Ortho—Para Hydrogen Conversion in the Detection of Free Radicals Produced in Photo-dissociation¹