ISOTOPE EFFECTS IN X-RAY-IRRADIATED ACIDIFIED H2O–D2O SOLUTIONS

1963 ◽  
Vol 41 (9) ◽  
pp. 2175-2186 ◽  
Author(s):  
Chava Lifshitz
Keyword(s):  
Isotope Effect ◽  
Molecular Hydrogen ◽  
Isotope Effects ◽  
Recombination Reaction ◽  
X Rays ◽  
Acid Solutions ◽  
Hydrogen Atoms ◽  
Radiation Chemical ◽  
X Ray ◽  
Molecular Product

H2O–D2O mixtures containing 0.1–1 N H2SO4 were irradiated by 200-kv X rays. The molecular isotope effect, [Formula: see text], was determined from experiments on KBr solutions. The atomic isotope effect, [Formula: see text], was determined from experiments on ethanol solutions. At 96% D2O, αA = 3.7 ± 0.5 and αM = 4.0 ± 0.2. The isotope effects are discussed in connection with the radiation-chemical reaction H3O+ + eH2O → H + 2H2O. The connection between the atomic and molecular hydrogen is discussed. It is concluded that the relation between the observed atomic and molecular isotope effects is not contrary to a hydrogen atom recombination reaction leading to the molecular product. Isotope effects due to the oxidation of Fe+2 ions by hydrogen atoms in acid solutions were measured and the mechanism of this reaction is discussed.

The action of X-rays on ferrous and ferric salts in aqueous solutions

1952 ◽  
Vol 211 (1106) ◽  
pp. 375-398 ◽  
Keyword(s):  
Molecular Hydrogen ◽  
Ph Dependence ◽  
Oh Radicals ◽  
Specific Rate ◽  
X Rays ◽  
Ferrous Ions ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
Specific Rate Constant ◽  
Theoretical Considerations

The action of X-rays on the ferrous-ferric system has been studied under a variety of conditions. The H atoms and OH radicals formed primarily by the action of the radiation on the water react according to Fe 3+ + H → Fe 2+ + H + and Fe 2+ + OH → Fe 3+ + OH - . Experiments carried out in the presence of molecular hydrogen, where the latter reaction competes with the reaction H 2 + OH → H 2 O + H, permit us to deduce that the specific rate constant of the reaction between OH radicals and ferrous ions is about five times greater than that of the corresponding reaction with hydrogen molecules. The study of the pH dependence of the reaction has led to the assumption that molecular hydrogen ions, H + 2(hydr.) , intervene in this process undergoing the reaction Fe 2+ + H + 2(hydr.) → Fe 3+ + H 2 , and that these ions exist in the equilibrium: H + H + (hydr.) ⇌ H + 2(hydr.) . Experimental evidence and some theoretical considerations which have led to the assumption of H + 2 in aqueous systems have been discussed in detail. In the presence of molecular oxygen the hydrogen atoms react according to H + O 2 → HO 2 , followed by reactions of the latter radical (cf. Haber & Weiss 1934). A comparison of the experimentally determined yields under different conditions with the absolute (chemical) yields as derived from the proposed mechanism has led to the estimation of the energy ( W H 2 O ) required for the production of a radical pair (H + OH) by the action of X-rays on water. This has been found to be W H 2 O = 19⋅4 ± 0⋅4 eV.

Isotope effects in solution small-angle X-ray scattering

1999 ◽  
Vol 32 (1) ◽  
pp. 113-114 ◽  
Author(s):  
Stephen J. Henderson
Keyword(s):  
Neutron Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Isotope Effects ◽  
X Rays ◽  
Light Water ◽  
X Ray ◽  
X Ray Scattering ◽  
The Difference ◽  
Ray Scattering

While the difference between using heavy and light water as solvents for small-angle neutron scattering experiments is well known, the lesser difference for the case of small-angle X-ray scattering with these same isotopes of water has, as yet, not been reported. This difference for the case of X-rays is discussed and quantified for several familiar materials: polystyrene latexes, proteins and lipids.

scholarly journals Photon-dominated and X-ray dominated regions

1997 ◽  
Vol 178 ◽  
pp. 141-154 ◽  
Author(s):  
A. Sternberg ◽  
Min Yan ◽  
A. Dalgarno
Keyword(s):  
Molecular Hydrogen ◽  
Infrared Emission ◽  
Time Dependent ◽  
Chemical Characteristics ◽  
X Rays ◽  
X Ray

A brief account is presented of the chemical characteristics of regions controlled by the absorption of X-rays. Recent studies of the infrared emission from molecular hydrogen and time-dependent effects in evolving photon-dominated regions are summarized.

ABLATION OF POLY(METHYL METHACRYLATE) BY A SINGLE PULSE OF SOFT X-RAYS EMITTED FROM Z-PINCH AND LASER-PRODUCED PLASMAS

2002 ◽  
Vol 09 (01) ◽  
pp. 347-352 ◽  
Author(s):  
L. JUHA ◽  
J. KRÁSA ◽  
A. PRÄG ◽  
A. CEJNAROVÁ ◽  
D. CHVOSTOVÁ ◽  
...  
Keyword(s):  
Methyl Methacrylate ◽  
Single Pulse ◽  
Polymer Structure ◽  
Molecular Fragment ◽  
X Rays ◽  
Radiation Chemical ◽  
X Ray ◽  
Poly Methyl Methacrylate ◽  
Promising Application ◽  
Z Pinch

The efficiency of ablation induced in poly(methyl methacrylate) (PMMA) by single soft X-ray pulses emitted from Z-pinch and laser-produced plasmas was determined. X-ray ablation of PMMA was found to be less efficient than that of teflon (PTFE). Nonthermal effects of the radiation on the polymer structure play a key role in the mechanisms of the ablation, i.e. the ablation can be explained by the formation of radiation-chemical scissions of the polymer chain followed by blowoff of low-molecular fragment fluid into the vacuum. The most promising application of this phenomenon seems to be micropatterning/micromachining.

ISOTOPE EFFECTS IN NEUTRAL H2O–D2O IRRADIATED SOLUTIONS AND THE NATURE OF THE REDUCING RADICAL

1962 ◽  
Vol 40 (10) ◽  
pp. 1903-1908 ◽  
Author(s):  
Chava Lifshitz
Keyword(s):  
Hydrogen Atom ◽  
Water Molecule ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Sodium Formate ◽  
Alternative Possibilities ◽  
X Rays ◽  
Deuterium Isotope Effect ◽  
Deuterium Concentration ◽  
Single Water Molecule

Neutral solutions of sodium formate in H2O–D2O mixtures were irradiated by 200-kv X rays. The atomic deuterium isotope effect (αA) and its dependence on deuterium concentration were determined. In a 1 × 10−1 M HCOONa, 96% D2O solution, G(hydrogen) = 1.14 and αA = 4.3. It is concluded that the hydrogen atom cannot be formed from a single water molecule. Possible mechanisms of hydrogen atom formation are discussed. The alternative possibilities for the atoms to react as H or H2O− are viewed in the light of the proposed mechanisms.

DEUTERIUM ISOTOPE EFFECTS IN ABSTRACTION OF HYDROGEN ATOMS FROM PHENOLS

1962 ◽  
Vol 40 (4) ◽  
pp. 701-704 ◽  
Author(s):  
R. A. Bird ◽  
G. A. Harpell ◽  
K. E. Russell
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Isotope Effects ◽  
Hydrogen Abstraction ◽  
Degree Of Polymerization ◽  
Hydrogen Atoms ◽  
Transfer Constant ◽  
Deuterium Isotope Effects

The effect of six deuterated phenols on the rate and degree of polymerization of styrene has been studied. The rate and degree of polymerization are decreased by deuterated phenols to a much less extent than by the corresponding phenols. Approximate transfer constants are estimated, and it is found that the transfer constant for hydrogen abstraction from the deuterated phenol is less than 0.2 of the transfer constant for the normal phenol. The rates of reaction of 2,2-diphenyl-1-picrylhydrazyl with three deuterated phenols have been determined. The rate constants for deuterated 2,6-di-t-butylphenol and 4-bromophenol are less than 0.15 of those for the corresponding phenols, but the isotope effect appears to be small with 4-nitrophenol.

TAAM: a reliable and user friendly tool for hydrogen-atom location using routine X-ray diffraction data

2020 ◽  
Vol 76 (3) ◽  
pp. 296-306 ◽  
Author(s):  
Kunal Kumar Jha ◽  
Barbara Gruza ◽  
Prashant Kumar ◽  
Michal Leszek Chodkiewicz ◽  
Paulina Maria Dominiak
Keyword(s):  
Neutron Diffraction ◽  
Diffraction Data ◽  
Structure Refinement ◽  
X Rays ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Bond Lengths ◽  
Atom Model ◽  
User Friendly

Hydrogen is present in almost all of the molecules in living things. It is very reactive and forms bonds with most of the elements, terminating their valences and enhancing their chemistry. X-ray diffraction is the most common method for structure determination. It depends on scattering of X-rays from electron density, which means the single electron of hydrogen is difficult to detect. Generally, neutron diffraction data are used to determine the accurate position of hydrogen atoms. However, the requirement for good quality single crystals, costly maintenance and the limited number of neutron diffraction facilities means that these kind of results are rarely available. Here it is shown that the use of Transferable Aspherical Atom Model (TAAM) instead of Independent Atom Model (IAM) in routine structure refinement with X-ray data is another possible solution which largely improves the precision and accuracy of X—H bond lengths and makes them comparable to averaged neutron bond lengths. TAAM, built from a pseudoatom databank, was used to determine the X—H bond lengths on 75 data sets for organic molecule crystals. TAAM parametrizations available in the modified University of Buffalo Databank (UBDB) of pseudoatoms applied through the DiSCaMB software library were used. The averaged bond lengths determined by TAAM refinements with X-ray diffraction data of atomic resolution (d min ≤ 0.83 Å) showed very good agreement with neutron data, mostly within one single sample standard deviation, much like Hirshfeld atom refinement (HAR). Atomic displacements for both hydrogen and non-hydrogen atoms obtained from the refinements systematically differed from IAM results. Overall TAAM gave better fits to experimental data of standard resolution compared to IAM. The research was accompanied with development of software aimed at providing user-friendly tools to use aspherical atom models in refinement of organic molecules at speeds comparable to routine refinements based on spherical atom model.

The Radiolysis of Water Vapor at Very High Dose Rates. II. Isotope Effects in the Hydrogen Yield from H2O–D2O Mixtures

1973 ◽  
Vol 51 (24) ◽  
pp. 4056-4061 ◽  
Author(s):  
A. W. Boyd ◽  
C. Willis ◽  
O. A. Miller
Keyword(s):  
Water Vapor ◽  
Isotope Effect ◽  
Isotope Effects ◽  
High Dose ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
Dose Rates ◽  
Very High

The isotope effect in the formation of hydrogen has been measured for H2O–D2O mixtures (10–90% H2O, 0.5–1.0 mg ml−1, 412–138 °C) with and without 1 mol% SF6 at 2 × 1027 eV g−1 s−1. The values of α ((H/D) radiolytic hydrogen/(H/D) H2O–D2O) for the reactions of hydrogen atoms are in the range 3–6 varying with H/D ratio of the substrate. Consideration of possible mechanisms for these large α values leads to the conclusions that reaction of the hydrogen atoms to form hydrogen involves the substrate and that the species H3O may be formed as an intermediate.

SOME DEUTERIUM ISOTOPE EFFECTS: I. WATER SOLVOLYSIS OF METHYL-d3 ESTERS

1960 ◽  
Vol 38 (2) ◽  
pp. 222-232 ◽  
Author(s):  
J. A. Llewellyn ◽  
R. E. Robertson ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Hydrogen Atoms ◽  
Deuterium Isotope Effect ◽  
Methyl Group ◽  
Out Of Plane ◽  
Thermodynamic Effects ◽  
Inverse Isotope Effect ◽  
Activated Complex

The α-deuterium isotope effect has been examined for the solvolysis of a series of esters containing a fully deuterated methyl group. The possible sources of the effect have been divided into "thermodynamic" effects which appear to favor more rapid reaction of the protium compound and "zero point" effects where stiffening of out-of-plane vibrations may account for the direction of the observed isotope effects. It appears that the inverse isotope effect may be a measure of the spatial restrictions placed on the hydrogen atoms on the carbon atom in the activated complex.

Sign in / Sign up

Export Citation Format

Share Document