Photoinitiated hydrogen-atom reactions in carbon dioxide-hydrogen bromide complexes

1991 ◽  
Vol 95 (21) ◽  
pp. 8048-8053 ◽  
Author(s):  
Seung Koo Shin ◽  
Curt Wittig ◽  
William A. Goddard
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Hydrogen Bromide

Radiolysis of aqueous 2,2,2-tribromoethanol solutions

1970 ◽  
Vol 48 (16) ◽  
pp. 2542-2548 ◽  
Author(s):  
V. G. Sorensen ◽  
V. M. Bhale ◽  
K. J. McCallum ◽  
R. J. Woods
Keyword(s):  
Carbon Dioxide ◽  
Dose Rate ◽  
Glycolic Acid ◽  
Hydrogen Bromide ◽  
Photochemical Decomposition ◽  
Bromide Ion ◽  
Presence And Absence ◽  
Effect Of Oxygen

Hydrogen bromide, glycolic acid, and carbon dioxide have been identified as products of the γ-radiolysis of aqueous 2,2,2-tribromoethanol solutions. The effect of oxygen, tribromoethanol concentration, and dose rate upon the yields of bromide ion and acid have been determined, and partial radiolysis mechanisms are proposed for reaction in the presence and absence of oxygen. Dibromoacetaldehyde, reported to be a product of the photochemical decomposition of tribromoethanol solutions, was not detected in the radiolysis experiments or in tribromoethanol solutions exposed to sunlight.

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

2013 ◽  
Vol 91 (2) ◽  
pp. 155-168
Author(s):  
Waled Tantawy ◽  
Ahmed Hashem ◽  
Nabil Yousif ◽  
Eman Flefel
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Bond ◽  
Electron Transfer ◽  
Hydrogen Atom ◽  
Transfer Process ◽  
Carbonyl Compounds ◽  
Hydrogen Atom Transfer ◽  
Transfer Reactions ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer

The thermochemistry of the hydrogen atom transfer reactions from the H2O–BX2 radical system (X = H, CH3, NH2, OH, F) to carbon dioxide, formic acid, and (or) formaldehyde, which produce hydroxyformyl, dihydroxymethyl, and hydroxymethyl radicals, respectively, were investigated theoretically at ROMP2/6–311+G(3DF,2P)//UB3LYP/6–31G(D) and UG3(MP2)-RAD levels of theory. Surprisingly, in the cases of a strong Lewis acid (X = H, CH3, F), the spin transfer process from the water–boryl radical to the carbonyl compounds was barrier-free and associated with a dramatic reduction in the B–H bond dissociation energy (BDE) relative to that of isolated water–borane complexes. Examining the coordinates of these reactions revealed that the entire hydrogen atom transfer process is governed by the proton-coupled electron transfer (PCET) mechanism. Hence, the elucidated mechanism has been applied in the cases of weak Lewis acids (X = NH2, OH), and the variation in the accompanied activation energy was attributed to the stereoelectronic effect interplaying in CO2 and HCOOH compared with HCHO. We ascribed the overall mechanism as a SA-induced five-center cyclic PCET, in which the proton transfers across the so-called complexation-induced hydrogen bond (CIHB) channel, while the SOMOB–LUMOC=O′ interaction is responsible for the electron migration process. Owing to previous reports that interrelate the hydrogen-bonding and the rate of proton-coupled electron-transfer reactions, we postulated that “the rate of the PCET reaction is expected to be promoted by the covalency of the hydrogen bond, and any factor that enhances this covalency could be considered an activator of the PCET process.” This postulate could be considered a good rationale for the lack of a barrier associated with the hydrogen atom transfer from the water-boryl radical system to the carbonyl compounds. Light has been shed on the water–boryl radical reagent from the thermodynamic perspective.

Vacuum ultra-violet flash photolysis of water vapour

1962 ◽  
Vol 266 (1325) ◽  
pp. 185-197 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Complex Formation ◽  
Hydroxyl Radical ◽  
Water Vapour ◽  
Iodine Atom ◽  
Flash Photolysis ◽  
Ultra Violet ◽  
Kinetics Of ◽  
Vacuum Ultra Violet

An apparatus for effecting flash photolysis in the vacuum ultra-violet region is described. Appreciable decompositions of water, carbon dioxide, acetylene, ethylene and methane were effected with a 2000 J flash of 30 p .s duration. A detailed study of water vapour photolysis has established that, in the primary step, at least 90 % of the dissociation leads to a hydrogen atom and a hydroxyl radical. The kinetics of the hydroxyl radical disappearance, following flash photolysis of water vapour in the presence of various third bodies, has been studied. The rate constant is faster in xenon than in helium and other similarities with the data on iodine atom recombination suggest the operation of a mechanism involving intermediate complex formation.

DETERMINATION OF RATES OF CHANGE OF POLARIZABILITY FROM RAMAN AND RAYLEIGH INTENSITIES

1953 ◽  
Vol 31 (6) ◽  
pp. 954-961 ◽  
Author(s):  
E. J. Stansbury ◽  
M. F. Crawford ◽  
H. L. Welsh
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Chloride ◽  
Internuclear Distance ◽  
Hydrogen Bromide ◽  
Rate Of Change ◽  
Mean Values ◽  
Rates Of Change

Mean values of the rate of change of polarizability with respect to internuclear distance were determined for several molecules from the ratio of Raman and Ray-leigh intensities in the gas. The values obtained are: hydrogen, 1.2 × 10−16 cm.2; deuterium, 1.1; hydrogen chloride, 1.0; hydrogen bromide, 1.2; nitrogen, 1.6; oxygen, 1.4; carbon dioxide (ν1 vibration), 4.2; methane (ν1 vibration), 4.1. It is noteworthy that the values for the partially ionic molecules, hydrogen chloride and hydrogen bromide, are nearly the same as for hydrogen and deuterium.

scholarly journals Kinetic study of carbon dioxide catalytic methanation over cobalt–nickel catalysts

2019 ◽  
Vol 7 (1) ◽  
pp. 74-80 ◽  
Author(s):  
Alla G. Dyachenko ◽  
Olena V. Ischenko ◽  
Snizhana V. Gaidai ◽  
Tetiana M. Zakharova ◽  
Andrii V. Yatsymyrskyi ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
High Stability ◽  
Spectroscopic Analysis ◽  
Kinetic Equations ◽  
Nickel Catalysts ◽  
Carbon Dioxide Molecule ◽  
Cobalt Nickel ◽  
Limiting Step ◽  
Good Agreement

Based on the data of the thermoprogrammed desorption and using mass-spectroscopic analysis of desorbed products and on the kinetic patterns of the methanation process for cobalt–nickel catalysts, we suggested a mechanism for the reaction which passes through forming intermediate formyl compounds: CHO*, HCOH*, and HCOOH*. Because of the high stability of the carbon dioxide molecule, the step of adding the first hydrogen atom is the limiting step. Such a mechanism is in good agreement with the proposed kinetic equations.

Sign in / Sign up

Export Citation Format

Share Document