Hg(63P1)-sensitized decomposition of HNCO vapor and HNCO–H2 mixtures; the reaction of hydrogen atoms with HNCO

1968 ◽  
Vol 46 (4) ◽  
pp. 527-530 ◽  
Author(s):  
N. J. Friswell ◽  
R. A. Back
Keyword(s):  
Quantum Yield ◽  
Cross Section ◽  
Initial Step ◽  
Primary Process ◽  
Hydrogen Atoms ◽  
Direct Photolysis ◽  
A Value ◽  
The Cross

The Hg(63P1)-sensitized decomposition of HNCO vapor has been briefly studied at 26 °C with HNCO pressures from about 3 to 30 Torr. The products detected were the same as in the direct photolysis, CO, N2, and H2. The quantum yield of CO was appreciably less than unity, compared with a value of 1.5 in the direct photolysis under similar conditions. From this and other observations it is tentatively concluded that a single primary process occurs:[Formula: see text]From a study of the mercury-photosensitized reactions in mixtures of HNCO with H2, it was concluded that hydrogen atoms react with HNCO to form CO but not N2. The initial step is probably addition to form NH2CO. From the competition between reaction [1] and the corresponding quenching by H2, the cross section for reaction [1] was estimated to be 2.3 times that of hydrogen.

Measurements of the cross section for the production of hydrogen atoms in the metastable excited 2S state

1962 ◽  
Vol 3 (2) ◽  
pp. 62-63 ◽  
Author(s):  
L. Colli ◽  
F. Cristofori ◽  
G.E. Frigerio ◽  
P.G. Sona
Keyword(s):  
Cross Section ◽  
Hydrogen Atoms ◽  
Production Of Hydrogen ◽  
The Cross

The primary process in the photolysis of hexafluoroacetone vapour III. The efficiency of intersystem crossing

1968 ◽  
Vol 306 (1487) ◽  
pp. 529-536 ◽  
Keyword(s):  
Quantum Yield ◽  
Lower Limit ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Primary Process ◽  
Excited Singlet ◽  
A Value ◽  
Low Concentrations

The value of k 6 /( k 4 + k 5 + k 6 ) (mechanism of part I) was determined by two techniques, namely the sensitization of the isomerization of cis - to trans -butene-2 and the sensitization of the phosphorescence of biacetyl. Both techniques yielded a value for the ratio of 0⋅9 ± 0⋅1. The value obtained by the isomerization technique is a lower limit because the quantum yield for the isomerization did not attain a value independent of [ cis -butene-2], but reached a maximum at low concentrations of olefine and then decreased. A similar scavenging of the excited singlet state of hexafluoroacetone was observed when biacetyl was present as an addend. However, in both cases the measurements were made with sufficiently low concentrations of addend that the singlet scavenging should have introduced less, than 10% error. It is concluded that reaction (5) of the mechanism cannot be an important mode of disappearance of excited ketone molecules.

Primary process(es) in the mercury-photosensitized decomposition of dimethyl ether at 2537 Å

1968 ◽  
Vol 46 (16) ◽  
pp. 2693-2697 ◽  
Author(s):  
R. Payette ◽  
M. Bertrand ◽  
Y. Rousseau
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Light Intensity ◽  
Dimethyl Ether ◽  
Molecular Hydrogen ◽  
Room Temperature ◽  
Primary Process ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Radical Recombination

The mercury-photosensitized decomposition of dimethyl ether has been studied at room temperature and at pressures ranging from 10 to 200 Torr.The formation of an excited dimethyl ether (DME) molecule has been verified by following the rates of formation of methane, ethane, and carbon monoxide with various ether pressures.The study of the variation of the quantum yield of molecular hydrogen formation with absorbed light intensity at high ether pressures has shown that the primary process involves the dissociation of ether molecules into hydrogen atoms and methoxy methyl radicals:[Formula: see text]The results presented in this paper indicate that the excited DME molecule can originate in a radical recombination between hydrogen atoms and methoxy methyl radicals.

Monte-Carlo simulation of hydrogen-atom recombination

1973 ◽  
Vol 333 (1595) ◽  
pp. 419-434 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Cross Section ◽  
Rate Constant ◽  
Relative Velocity ◽  
Classical Trajectory ◽  
Hydrogen Atoms ◽  
Order Of Magnitude ◽  
The Cross ◽  
The Right ◽  
Right Order

Classical trajectory calculations have been used to calculate the cross-section (and hence the rate constant) for the recombination of hydrogen atoms on a third hydrogen atom, in the temperature range 500–6000 K. The model involves the stabilization of a quasi-bound molecule in an encounter with the third atom. The results indicate that the cross-section for direct stabilization is small and insensitive to the relative velocity, whereas the cross-section for exchange stabilization is large at low velocities and decreases rapidly as the relative velocity is increased. The calculated rate constant, although of the right order of magnitude at 500 K, does not exhibit the anomalous features previously observed experimentally at higher temperatures.

Spin-change cross-sections

1961 ◽  
Vol 262 (1308) ◽  
pp. 132-135 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Change Process ◽  
Change Processes ◽  
Hydrogen Atoms ◽  
Atomic Systems ◽  
The Cross

A quantal formulation of spin-change processes in collisions of atomic systems is presented. The cross-section for the spin-change process in the collision of two hydrogen atoms is computed for temperatures up to 10000°K and the results given in a table.

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

1973 ◽  
Vol 51 (5) ◽  
pp. 656-666 ◽  
Author(s):  
D. K. Jardine ◽  
N. M. Ballash ◽  
D. A. Armstrong
Keyword(s):  
Carbon Dioxide ◽  
Cross Section ◽  
Hydrogen Bromide ◽  
Gaseous Hydrogen ◽  
Initial Kinetic Energy ◽  
Zero Energy ◽  
Hydrogen Atoms ◽  
Abstraction Reaction ◽  
Thermal Region ◽  
The Cross

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.

scholarly journals Charge Exchange Collisions Involving Multielectron Atoms (Lithium and Sodium)

1968 ◽  
Vol 21 (6) ◽  
pp. 793 ◽  
Author(s):  
JG Lodge ◽  
RM May
Keyword(s):  
Excited State ◽  
Cross Section ◽  
Charge Exchange ◽  
Correction Factor ◽  
Ground State ◽  
Hydrogen Atoms ◽  
Sodium Atoms ◽  
The Cross ◽  
Multielectron Atoms

The cross section for forming both ground state and excited state hydrogen atoms by charge exchange between protons and lithium or sodium atoms is calculated. These calculations are performed using the Brinkman-Kramers approximation along with a multiplicative correction factor; the target lithium and sodium atoms are first described by simple "effective-Z" wavefunctions, and then the lithium case is treated more accurately both by including the inner electrons and by using a more accurate numerical lithium wavefunction.

THERMAL NEUTRON CAPTURE CROSS SECTION OF Ce142

1956 ◽  
Vol 34 (8) ◽  
pp. 1023-1026 ◽  
Author(s):  
L. P. Roy ◽  
L. Yaffe
Keyword(s):  
Thermal Neutron ◽  
Cross Section ◽  
Neutron Capture ◽  
Capture Cross Section ◽  
Activation Method ◽  
Thermal Neutron Capture ◽  
Capture Cross ◽  
Neutron Capture Cross Section ◽  
A Value ◽  
The Cross

The cross section of Ce142 has been determined by the activation method and found to be 0.95 ± 0.05 barns relative to a value of σCo59 = 36.3 barns. Disintegration rates were determined by a 4π counter. The value obtained agrees with that of Katcoff etal. (1949) also obtained by the activation method but differs markedly from that of Pomerance (1952).

Some calculations on the diffusion of slow neutrons in hydrogenous media

1937 ◽  
Vol 33 (1) ◽  
pp. 122-136 ◽  
Author(s):  
C. H. Westcott
Keyword(s):  
Water Molecule ◽  
Cross Section ◽  
Total Absorption ◽  
Absorption Cross ◽  
Hydrogen Atoms ◽  
Slowing Down ◽  
Research Award ◽  
A Value ◽  
Senior Research ◽  
Slow Neutrons

The paper describes calculations on the distribution in space of slow neutrons based on the application of diffusion laws to their motions. The effects of using spheres of different sizes, and of changing the composition of the hydrogenous slowing-down medium, are discussed. Curves are given which can be compared with the results of the experiments on the slowing down in different media carried out by the author in collaboration with Mr T. Bjerge, and a revision of the calculations based on these experiments leads to a value of 6 × 10−25 cm.2 for the total absorption cross-section of the water molecule, and indicates that most of this absorption must be attributed to the hydrogen atoms.The author desires to acknowledge the receipt of a Senior Research Award from the Department of Scientific and Industrial Research.

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