Hot Hydrogen Atoms Research Articles

Hot hydrogen atoms reactions and the mechanisms of liquid normal alkanes radiolysis

Abstract The published data on liquid n-alkanes radiolysis at low doses and temperatures of 0–25°C are considered. The mechanism of liquid n-alkanes radiolysis is suggested, including the reactions of hot hydrogen atom formation under irradiation and the processes of their stabilization similar to those of recoil tritium atoms in the same systems.

Isotope effects in hot atom abstraction reactions of hot hydrogen and hot deuterium atoms with ethane-1,1,1-d3

Hot H and D (H* and D*) reactions with ethane were studied in Br/sub 2/ scavenged systems using HBr and DBr as photodissociation hot atom sources. Quantum yields for the abstraction reactions of H* + C/sub 2/D/sub 6/ and H* + CH/sub 3/CD/sub 3/ were determined at an initial hot atom energy E/sub i/ = 1.6 eV, and found to be in good agreement with previous yields determined by the integral reaction probability method. Abstraction isotope effects for H* and D* + CH/sub 3/CD/sub 3/ were determined over the range E/sub i/ = 1.1 to 2.9 eV, in 94 percent ethane systems. With H* + CH/sub 3/CD/sub 3/ the H/sub 2//HD product ratio increased from 2.4 +- 0.1 at 1.1 eV to 2.8 +- 0.1 at 2.9 eV, whereas with D* + CH/sub 3/CD/sub 3/ the HD/D/sub 2/ product ratio was approximately constant with change in E/sub i/, 2.0 +- 0.1 at 1.6 eV and 1.9 +- 0.1 at 2.0 and 2.9 eV. In mixtures with a large mole fraction of Br/sub 2/ to scavenge low energy atoms the isotope effects at E/sub i/ = 2.9 eV increased to 3.1 +- 0.1 for H* + CH/sub 3/CD/sub 3/ and 2.8more » +- 0.4 for D* + CH/sub 3/CD/sub 3/. These results, taken together with a previous determination of the abstraction isotope effect in the T* + CH/sub 4/--CD/sub 4/ system at 2.9 eV, give a consistent trend favoring H over D abstraction, with the H/D isotope effect increasing with decreasing hot atom mass. It is concluded that both the H/D preference and the hot atom mass effect can be understood in terms of inertial considerations and that a zero point energy effect may also contribute to the H/D preference.« less

Gas phase radiation chemistry of ethyl bromide

The ..gamma.. radiolysis of ethyl bromide has been investigated at 100 Torr pressure and 23/sup 0/C. In the pure system between an absorbed dose of 1.0 x 10/sup 20/ and 1.5 x 10/sup 20/ eV/g the major products and their respective G values are as follows: hydrogen bromide, 3.89; ethane, 2.70; ethylene, 2.17; acetylene, 0.31; hydrogen, 1.39; 1,1-dibromoethane, 0.88; 1,2-dibromoethane, 0.12; vinyl bromide, 0.32; methane, 0.083; methyl bromide, 0.080; and bromoform, 0.0078. When oxygen is added, the G values in this dose range become the following: hydrogen bromide, 4.89; ethane, 0.31; ethylene, 0.78; acetylene, 0.27; hydrogen, 1.38; 1,1-dibromoethane, 0.028; 1,2-dibromoethane, 0.56; vinyl bromide, 0.0; methane 0.03; methyl bromide, 0.32; and bromoform, 0.0034. Bromine is also formed with a G value of 2.4 when oxygen is added. The presence of hydrogen and acetylene in the radiolysis indicates that these species must be formed from higher energy processes not accessible in the 253.7-nm photolysis, which was studied in a parallel investigation. The product distribution indicates that the probabilities of single bond rupture in the primary event are approximately C/sub 2/H/sub 5/--Br:C/sub 2/H/sub 4/Br--H:CH/sub 3/--CH/sub 2/Br = 1.00:0.40:0.06. Either a hot hydrogen atom abstraction reaction or direct molecular H/sub 2/ elimination accounts formore » about 16 percent of the hydrogen yield. Strong similarities in dose-yield plots suggest that many of the secondary processes involved in the photolysis are important in the radiolysis of ethyl bromide as well. The high pressure mass spectrometry of the system indicates the role of ionic species. Differences in radiolytic behavior of ethyl chloride, bromide, and iodide can largely be explained in terms of the energetics of the primary and secondary processes in each system.« less

Origin of organic compounds on the primitive earth and in meteorites.

The role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth, in the parent bodies or carbonaceous chondrites, and in the solar nebula are examined. A single source of energy or a single process would not account for all the organic compounds synthesized in the solar system. Electric discharges appear to produce amino acids more efficiently than other sources of energy and the composition of the synthesized amino acids is qualitatively similar to those found in the Murchison meteorite. Ultraviolet light is also likely to have played a major role in prebiotic synthesis. Although the energy in the sun's spectrum that can be absorbed by the major constituents of the primitive atmosphere is not large, reactive trace components such as H2S and formaldehyde absorb at longer wavelengths where greater amounts of energy are available and produce amino acids by reactions involving hot hydrogen atoms. The thermal reaction of CO + H2 + NH3 on Fischer-Tropsch catalysts generates intermediates that lead to amino acids and other organic compounds that have been found in meteorites. However, this synthesis appears to be less efficient than electric discharges and to require a special set of reaction conditions. It should be emphasized that after the reactive organic intermediates are generated by the above processes, the subsequent reactions which produce the more complete biochemical compounds are low temperature homogenous reactions occurring in an aqueous environment.

The Estimation of the G-Values for Ionization and Excitation of Ten-Electron Molecules: Methane, Ammonia, and Water Irradiated by 100 keV Electrons

Abstract The binary-encounter collision theory is applied to calculate the G-values for the ionization and excitation of methane, ammonia, and water irradiated by 100 keV electrons. Double collision of the incident electron in a molecule is also taken into account. On the assumption of the occurrence of certain reactions in the systems, the G-values for electrons, various radicals, and several final products were estimated. Some of the results are as follows: the G-values for electrons were 3.60 for methane, 3.56 for ammonia, and 3.00 for water. These values are in fair agreement with the experimental values: 3.6 for methane, 3.8 for ammonia, and 3.3 for water. The calculated G-value for hot hydrogen atoms was about 1.0 for all three compounds. The ratios of the G-value for excitation to that for electrons are 1.1 for methane, 1.5 for ammonia, and 1.7 for water. An estimation was also made of the G-value for the emission of highly-excited hydrogen atoms using reported cross sections. The G-values are 0.1 for methane and ammonia, and 0.2 for water.

Fragmentation of excited molecules and ions in the radiolysis of hydrocarbons

A survey is given of recent studies of the primary CH and CC bond dissociations of excited molecules and ions in the gas- and liquid-phase radiolysis of hydrocarbons, which have been mainly carried out by the product analysis method. In the CC bond dissociations evidence has been presented for the fragmentation of the excited parent ion, while in the CH bond dissociations attention has been focused upon an important role of hot hydrogen atoms in the hydrogen formation. A theoretical treatment of highly excited hydrocarbon molecules involving super-excited states is also described.

On the photolysis of methanethiol and ethanethiol at 185 nm

Quantum yields for the formation of hydrogen and methane in the photolysis of methanethiol at 185 nm are 0.70 ± 0.03 and 0.26 ± 0.02, respectively. At the same wavelength ethanethiol gives quantum yields of 0.62 ± 0.01, 0.30 ± 0.01, and 0.07 ± 0.01 for hydrogen, ethane, and ethylene respectively. In both cases the sum of these quantum yields is unity, independent of thiol pressure. The data are treated in terms of a mechanism which also accounts for earlier work at 254 and 214 nm. Hot hydrogen atom reactions are invoked as a result of thermalization effects observed when n-butane or perfluorodimethylcyclobutane is mixed with the thiol. Decreases, with increasing photon energy, in the ratio of SH to CS bond cleavage are noted and correlated with earlier work on the spectra and molecular orbitals of the parent compounds. Satisfactory correlations are also noted between the average energy of the photochemically produced hydrogen atoms and the fraction of these atoms which undergo energy sensitive reactions.

Hot Hydrogen in Prebiological and Interstellar Chemistry

Two articles discuss the recent experimental work of Hong et al. on the production of amino acids and gas-phase organic compounds from the ultraviolet irradiation of simple gases, with hot hydrogen atoms used as the principal energy conversion agent. The reaction possibilities involving frozen ices are mentioned in both articles, as well as the significance of three-body collisions in this situation.

On the photolysis of methanethiol and ethanethiol at 185 nm

Quantum yields for the formation of hydrogen and methane in the photolysis of methanethiol at 185 nm are 0.70 ± 0.03 and 0.26 ± 0.02, respectively. At the same wavelength ethanethiol gives quantum yields of 0.62 ± 0.01, 0.30 ± 0.01, and 0.07 ± 0.01 for hydrogen, ethane, and ethylene respectively. In both cases the sum of these quantum yields is unity, independent of thiol pressure. The data are treated in terms of a mechanism which also accounts for earlier work at 254 and 214 nm. Hot hydrogen atom reactions are invoked as a result of thermalization effects observed when n-butane or perfluorodimethylcyclobutane is mixed with the thiol. Decreases, with increasing photon energy, in the ratio of SH to CS bond cleavage are noted and correlated with earlier work on the spectra and molecular orbitals of the parent compounds. Satisfactory correlations are also noted between the average energy of the photochemically produced hydrogen atoms and the fraction of these atoms which undergo energy sensitive reactions.

Xenon-sensitized radiolysis of hydrogen sulphide in the presence of HBr, N2O, CCl4, and SF6

Abstract The γ-radiolysis of hydrogen sulphide in the excess of xenon : as studied as a function of added HBr, N2O, CCl4 and SF6. Addition of HBr results in the considerable increase of H2 yield while addition of excess of N2O, CGl4 and SF6 reduces G(H 2 ) to almost zero. When N2O is present, the N2 yield also varies with the H2S/N2O ratio, being uninfluenced by the addition of small amounts of SF6 Consideration of possible ionic and nonionic reactions leads to the conclusion that hot hydrogen atoms play a major role in the formation both of hydrogen and nitrogen. The mechanism of electron attachment and ion recombination processes is proposed which is consistent with all the obtained data.

Hot hydrogen atoms reactions of interest in molecular evolution and interstellar chemistry.

Hot hydrogen atoms which are photochemically generated initiate reactions among mixtures of methane, ethane, water and ammonia, to produce ethanol, organic amines, organic acids, and amino acids. Both ethanol and ethyl amine can also act as substrates for formation of amino acids. The one carbon substrate methane is sufficient as a carbon source to produce amino acids. Typical quantum yields for formation of amino acids are approximately 2–4 · 10-5. In one experiment, 6 protein amino acids were identified and 8 non-protein amino acids verified utilizing gas chromatography-mass spectroscopy. We propose that hot atoms, especially hydrogen, initiate reactions in the thermodynamic non-equilibrium environment of interstellar space as well as in the atmospheres of planets.

Hot Hydrogen Atoms: Initiators of Reactions of Interest in Interstellar Chemistry and Evolution

Photochemically generated hot hydrogen atoms initiate reactions with simple molecular substrates including methane to produce organic alcohols, amines, acids, amino acids, and other compounds. The typical quantum yields for the formation of amino acids are 2 x 10(-5) to 4 x 10(-5). Hot hydrogen atoms may be important initiators of reactions in interstellar space and in planetary atmospheres.

Yields of elementary reactions initiated when HI and DI are activated by 254 nm radiation in 3-methylpentane-h14 and 3MP-d14 at 20–300 °K; H atom trapping

This paper reports work designed to give a more quantitative understanding of the reactions of hot and thermal hydrogen atoms with hydrocarbons at 298, 77, and 30°K and to explain the absence of trapped H atoms during photolysis of HI in 3-methylpentane-h14 (3MP-h14) glass at 30°K. Quantum yields of H2, HD, and D2 from the photolysis of HI and DI in 3MP-h14 have been determined for samples photolyzed in the liquid state at 298°K and the glassy state at 77 and 30°K. The yields of trapped free radicals and of alkyl iodides and iodine have been determined on samples photolyzed at 77°K. Trapped hydrogen atoms have been produced by photolysis of HI in 3-methylheptane-d18 and methylcyclohexane-d14 glasses, and their production in 3MP-d14 and nonproduction in 3MP-h14 confirmed. Photolysis of HI in 3MP-d14 at 30°K yields H2 as well as HD, indicating that thermalized H atoms are produced, but photolysis of DI in 3MP-h14 at 30°K yeilds no D2. This indicates that all the D atoms produced in 3MP-h14 abstract H from C–H bonds and implies that the reason D and H atoms from the photolysis of DI and HI in 3MP-h14 are not trapped is because the abstraction reaction consumes all of the atoms before they can be trapped. Information on isotope effects in both the liquid and solid phase has been obtained. The data further indicate that: (1) the quantum yield for stabilization of HI (DI) without reaction after having absorbed a photon is about 0.13 at 298°K and 0.5 at 77°K, in either 3MP-h14 or 3MP-d14; (2) the yield of HD from HI in 3MP-d14 or DI in 3MP-h14 at 77 °K is much greater than the yield of trapped radicals, implying that C6D13I(C6H13I) + HD must be formed by a concerted reaction; (3) at 298 °K the reaction D+3MP-h14 competes significantly for thermalized D atoms with the atom scavenging reaction D+DI→D2+I at DI concentrations less than ∼100 mM.

ChemInform Abstract: HYDROGEN FORMATION IN THE GAS‐PHASE RADIOLYSIS OF C2H4‐D2O MIXTURES

Chemischer InformationsdienstVolume 5, Issue 8 Preparative Organic Chemistry ChemInform Abstract: HYDROGEN FORMATION IN THE GAS-PHASE RADIOLYSIS OF C2H4-D2O MIXTURES KEN-ICHI KUWABARA, KEN-ICHI KUWABARASearch for more papers by this authorYOSHIHIKO HATANO, YOSHIHIKO HATANOSearch for more papers by this author KEN-ICHI KUWABARA, KEN-ICHI KUWABARASearch for more papers by this authorYOSHIHIKO HATANO, YOSHIHIKO HATANOSearch for more papers by this author First published: February 26, 1974 https://doi.org/10.1002/chin.197408135Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume5, Issue8February 26, 1974 RelatedInformation

Hydrogen Formation in the Gas-Phase Radiolysis of C2H4–D2O Mixtures

Abstract The total hydrogen yields and their isotopic compositions have been measured in the gas-phase radiolysis of C2H4–D2O mixtures at room temperature. A mixture of D2O (<10 mol %) with a large amount of C2H4 was used to avoid the effect of the wall on the decomposition of D2O. The contribution of thermal hydrogen atoms to the hydrogen formation may reasonably be excluded in this system. The kinetic treatment of D2 and HD formation suggests the decomposition mechanism of D2O. No important contribution of hot hydrogen atoms was observed. The yield of hydrogen from the D2O formed by the unimolecular process, G1D=0.4, was nearly equal to the molecular hydrogen yield reported previously.

ChemInform Abstract: THE 2288 A PHOTOLYSIS OF HYDROGEN IODIDE IN THE PRESENCE OF ETHYLENE AND PROPYLENE

Chemischer InformationsdienstVolume 4, Issue 35 Preparative Organic Chemistry ChemInform Abstract: THE 2288 A PHOTOLYSIS OF HYDROGEN IODIDE IN THE PRESENCE OF ETHYLENE AND PROPYLENE YASUHISA SANO, YASUHISA SANOSearch for more papers by this authorSHIN SATO, SHIN SATOSearch for more papers by this author YASUHISA SANO, YASUHISA SANOSearch for more papers by this authorSHIN SATO, SHIN SATOSearch for more papers by this author First published: August 28, 1973 https://doi.org/10.1002/chin.197335149AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue35August 28, 1973 RelatedInformation

Reaction of hot hydrogen atoms with methanethiol

First Page

The 2288 Å Photolysis of Hydrogen Iodide in the Presence of Ethylene and Propylene

Abstract The photolysis of hydrogen iodide at 2288 Å has been investigated in the presence of ethylene or propylene. The combinations studied were DI-C2H4, HI-C2D4, and DI-C3H6. In all combinations, the formation of a large amount of HD was observed; this may be attributed to the reaction of hot hydrogen atoms. The pressure dependence of the relative yields of HD and total hydrogen suggested that, of the two possible hot hydrogen atom reactions with ethylene, the abstraction reaction, D*+C2H4→C2H3+HD (2) does not occur, while the substitution reaction, D*+C2H4→C2H3D+H (3) is the important process. In the case of propylene, however, the abstraction of H by D* is important for the formation of HD. The measured ratios of C2H3D/HD in the DI–C2H4 system and of C2D3H/HD in the HI–C2D4 system were consistent with the above conclusion. Reaction (3) is probably not a real substitution reaction, but a combination of the addition reaction of a hydrogen atom to ethylene and the rapid decomposition of the excited ethyl radical produced.

Reactions of Hot Hydrogen Atoms in Gaseous Hydrogen Chloride and Hydrogen Bromide

Hydrogen atoms of initial kinetic energy E0 = 1.15 or 2.1 eV were produced photolytically and their reactions with HCl were studied at 300 °K using bromine as a scavenger. The fraction, FH, undergoing reaction 2 while hot was found to be 0.79 ± 0.02 and 0.55 ± 0.02 for E0 = 2.1 and 1.15 eV, respectively.[Formula: see text]For 2.1 eV atoms a similar result was obtained at 200 °K with chlorine as scavenger. On the addition of carbon dioxide as a moderator FH decreased in a manner consistent with the kinetic theory of hot atom reactions. Comparison of the present results with previous work on the D + DCl abstraction reaction showed that the cross section of the latter is probably 20 to 50% higher than that of H + HCl. The cross section of reaction 2 appears to increase with energy over most of the 0.1 to 1.1 eV range and possibly also above it. Its average magnitude over this energy region was estimated to be [Formula: see text].For atoms of E0 = 1.15 eV reacting in HBr FH is close to unity. The threshold of reaction 3′[Formula: see text]is near zero energy and its cross section rises rapidly, becoming [Formula: see text] in the thermal region for 300 °K.

The Reaction of Hot Hydrogen Atoms with Ethylene

The Reaction of Hot Hydrogen Atoms with Ethylene