Exchange mechanism and Arrhenius parameters of elementary steps in the reaction of hydrogen atoms with water vapor in irradiated mixtures of hydrogen and water vapor

1972 ◽  
Vol 76 (5) ◽  
pp. 621-630 ◽  
Author(s):  
N. E. Bibler ◽  
R. F. Firestone
Keyword(s):  
Water Vapor ◽  
Exchange Mechanism ◽  
Hydrogen Atoms ◽  
Arrhenius Parameters ◽  
Elementary Steps

Fluorescence Emission of Excited Hydrogen Atoms after Core Excitation of Water Vapor

2006 ◽  
Vol 96 (6) ◽  
Author(s):  
E. Melero García ◽  
A. Kivimäki ◽  
L. G. M. Pettersson ◽  
J. Álvarez Ruiz ◽  
M. Coreno ◽  
...  
Keyword(s):  
Water Vapor ◽  
Fluorescence Emission ◽  
Hydrogen Atoms ◽  
Core Excitation

scholarly journals Two types of quasi-liquid layers on ice crystals are formed kinetically

2016 ◽  
Vol 113 (7) ◽  
pp. 1749-1753 ◽  
Author(s):  
Harutoshi Asakawa ◽  
Gen Sazaki ◽  
Ken Nagashima ◽  
Shunichi Nakatsubo ◽  
Yoshinori Furukawa
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Thin Layers ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Crystal Surfaces ◽  
Fixed Temperature ◽  
Elementary Steps ◽  
Ice Surfaces

Surfaces of ice are covered with thin liquid water layers, called quasi-liquid layers (QLLs), even below their melting point (0 °C), which govern a wide variety of phenomena in nature. We recently found that two types of QLL phases appear that exhibit different morphologies (droplets and thin layers) [Sazaki G. et al. (2012) Proc Natl Acad Sci USA 109(4):1052−1055]. However, revealing the thermodynamic stabilities of QLLs remains a longstanding elusive problem. Here we show that both types of QLLs are metastable phases that appear only if the water vapor pressure is higher than a certain critical supersaturation. We directly visualized the QLLs on ice crystal surfaces by advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on ice crystal surfaces. At a certain fixed temperature, as the water vapor pressure decreased, thin-layer QLLs first disappeared, and then droplet QLLs vanished next, although elementary steps of ice crystals were still growing. These results clearly demonstrate that both types of QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. To our knowledge, this is the first experimental evidence that supersaturation of water vapor plays a crucially important role in the formation of QLLs.

Determination of the Rates of Hydrogen Atom Reaction with NO by a Modulation Technique

1973 ◽  
Vol 51 (3) ◽  
pp. 370-372 ◽  
Author(s):  
R. Atkinson ◽  
R. J. Cvetanović
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Atom ◽  
Phase Shift ◽  
Rate Constants ◽  
Hydrogen Atoms ◽  
Arrhenius Parameters ◽  
Modulation Technique ◽  
The Absolute

A modulation technique has been used to determine from phase shift measurements the absolute values of the rate constants and the Arrhenius parameters of the reaction of hydrogen atoms with nitric oxide.

An Overview of Aeronomic Processes in the Stratosphere and Mesosphere

1974 ◽  
Vol 52 (8) ◽  
pp. 1381-1396 ◽  
Author(s):  
M. Nicolet
Keyword(s):  
Nitric Oxide ◽  
Water Vapor ◽  
Nitric Acid ◽  
Oxygen Atom ◽  
Eddy Diffusion ◽  
Atmospheric Conditions ◽  
Hydrogen Atoms ◽  
Electronically Excited ◽  
The Vertical Distribution ◽  
Excited Oxygen

The discrepancy noted between theoretical and observational concentrations of O3 in the mesosphere and stratosphere can be explained by an effect of hydrogen compounds and of nitrogen oxides. Solar radiation dissociates water vapor and methane in the thermosphere and upper mesosphere. In the stratosphere the reaction of the excited oxygen atom O(1D) with methane and nitrous oxide leads to a destruction of these two molecules in the stratosphere which corresponds to a production of carbon monoxide with water vapor and of nitric oxide, respectively. Hydrogen and water vapor molecules also react with the electronically excited oxygen atom O(1D) leading to hydroxyl radicals. Insitu sources of H2 exist in the stratosphere and mesosphere: reaction of OH with CH1, photodissociation of formaldehyde, and also reaction between hydroperoxyl radicals and hydrogen atoms. The vertical distribution of water vapor is not affected by its dissociation in the stratosphere and mesosphere since its reformation is rapid.The ratio of the hydroxyl and hydroperoxyl radical concentrations cannot be determined with adequate precision and complicates the calculation of the destruction of ozone which occurs through reactions of OH and HO2 not only with atomic oxygen at the stratopause but also directly in the middle stratosphere and with CO and NO in the lower stratosphere.In addition to the various reactions involving nitric oxide and nitrogen dioxide, the reactions leading to the production and destruction of nitric acid and nitrous acid must be considered. Nitric acid molecules are involved in an eddy diffusion transport from the lower stratosphere into the troposphere and are, therefore, responsible for the removal of nitric oxide which is produced in the stratosphere. Atmospheric conditions must be known at the tropopause.

The X-radiolysis of water vapor containing methanol. Effects of some electron and hydrogen atom scavengers

1968 ◽  
Vol 46 (12) ◽  
pp. 1957-1964 ◽  
Author(s):  
R. S. Dixon ◽  
M. G. Bailey
Keyword(s):  
Nitrous Oxide ◽  
Water Vapor ◽  
Carbon Tetrachloride ◽  
Hydrogen Atom ◽  
Sulfur Hexafluoride ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
A Value ◽  
Ion Recombination ◽  
Positive Ion

The X-radiolysis of water vapor containing methanol at 125 °C and 1 atm pressure has been studied alone and in the presence of some electron and hydrogen atom scavengers. In water vapor containing methanol only, a plateau value G(H2) = 7.9 ± 0.3 is obtained at all methanol concentrations above 0.5 mole %. Addition of propylene drastically reduces this yield due to efficient scavenging of hydrogen atoms, and values for the total number of H atoms from all precursors g(H)t = 7,5 ± 0.2 and [Formula: see text] are deduced from the competition. An unscavengeable hydrogen yield g(H2) ~ 0.5 is also indicated in mixtures containing propylene. Nitrous oxide and sulfur hexafluoride are found to scavenge electrons efficiently in water vapor containing methanol and the number of hydrogen atoms arising from electron–positive ion recombination is estimated to have a value G = 2.2 ± 0.6. The number of hydrogen atoms arising from processes not involving electrons is g(H) = 5.2 ± 0.3. Carbon tetrachloride reacts efficiently with both electrons and hydrogen atoms, with k(H + CH3OH)/k(H + CCl4) = 0.085. Values of g(H) = 4.9 ± 0.5 and g(H2) = 0.8 ± 0.2 are deduced from mixtures containing carbon tetrachloride.

scholarly journals The distribution and saturation of water vapor as inferred from ACS during the first Martian year of TGO Science observations

2020 ◽  
Author(s):  
Anna Fedorova ◽  
Franck Montmessin ◽  
Oleg Korablev ◽  
Mikhail Luginin ◽  
Alexander Trokhimovskiy ◽  
...  
Keyword(s):  
Water Vapor ◽  
Vertical Distribution ◽  
Water Vapour ◽  
Atmospheric Chemistry ◽  
Water Distribution ◽  
Water Cycle ◽  
First Year ◽  
Hydrogen Atoms ◽  
Saturation State ◽  
Water Ice

<p>The water vapour vertical distribution is an eloquent gauge of the relative roles of the various sources, sinks and processes that control the Martian water cycle. However, its behaviour is still poorly studied while it is instrument for our understanding of the loss of water from Mars to space, which results from the transport of water to the upper atmosphere where it is disassociated to hydrogen atoms that later escape. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution with altitude. Here we present results of the Atmospheric Chemistry Suite (ACS) instrument NIR channel for the first year of TGO observations covering the almost full year from Ls 160° of the Martian year 34 (April 2018) to Ls 130° of the Martian year 35 (January 2020). Simultaneous measurements of the water vapour mixing ratio, temperature and dust vertical distribution and formation of water ice clouds allow us to constrain the complex water behaviour and estimate the saturation state of H2O. Water profiles during the 2018-2019 southern spring and summer stormy seasons show that high altitude water is preferentially supplied close to perihelion and that large supersaturation occurs even when clouds are present. Here we attempt to complete the story by studying water vapor during the northern spring and summer to explore whether saturation impacts water transport between hemispheres in this season. The data analysis of MY35 was supported by RSF (project No. 20-42-09035).</p>

High-Temperature Environmental Embrittlement of Thermomechanically Processed TiAl-Based Intermetallic Alloys with Various Kinds of Microstructures

2004 ◽  
Vol 842 ◽  
Author(s):  
T. Takasugi ◽  
Y. Hotta ◽  
S. Shibuya ◽  
Y. Kaneno ◽  
H. Inoue ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Temperature ◽  
Intermetallic Alloy ◽  
Hydrogen Gas ◽  
Tensile Fracture ◽  
Intermetallic Alloys ◽  
Hydrogen Atoms ◽  
Environmental Media ◽  
Environmental Embrittlement ◽  
Higher Temperature

ABSTRACTThermomechanically processed TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile tested in various environmental media including air, water vapor and a mixture gas of 5vol.%H2+Ar as a function of temperature. All the TiAl-based intermetallic alloys showed reduced tensile fracture stress (or elongation) in air, water vapor and a mixture gas of 5vol.%H2+Ar not only at ambient temperature (RT∼600K) but also at high temperature mostly from 600K to 1000K (sometimes higher temperature than 1000K). The high-temperature environmental embrittlement of TiAl-based intermetallic alloy depended upon the microstructure. The possible species causing the high-temperature environmental embrittlement are hydrogen atoms decomposed from water vapor (H2O) or hydrogen gas (H2), similar to those causing the low-temperature environmental embrittlement.

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