Quantum Yield Of Hydrogen Research Articles

Possible photochemical action of high-power laser radiation on fog droplets

It is shown that fog water droplets may scatter ultraviolet laser radiation as a result of photodissociation of molecules in liquid water. Estimates are obtained of the power of the fourth harmonic of picosecond ruby laser pulses necessary for the conversion of a water droplet of 2-μ radius into a mixture of gases. The quantum yield of hydrogen as a result of photolysis of liquid water is assumed to be 0.022 molecules per photon. The necessary energy density per pulse is ~700 I/cm2.

La décomposition du tétraméthylgermane par les atomes Hg 6(3P1)

The primary process in the mercury photosensitized decomposition of tetramethylgermane is a C—H bond cleavage. The hydrogen quantum yield, extrapolated at infinite pressure, is close to unity. Under mild conditions, hydrogen and 1,2-di(trimethylgermyl) ethane are the only products observed. At high intensities and low substrate pressures, atomic cracking occurs yielding methyl radicals which lead to the formation of methane.

PHOTOLYSIS OF AQUEOUS SOLUTIONS OF POTASSIUM CIS‐DIAQUOBIS (OXALATO) CHROMATE (III)

Abstract— The photolysis of aqueous solutions of cis‐[Cr(C2O4)2(H2O)2]‐ at 254 nm and pH 4 produced CO2 and H2 in nearly equal yields. The quantum yield of hydrogen, φ2, increased by 9% and the yield of carbon dioxide, φ, by 65% as the pH was lowered from 4 to I. The total gas yield, φgas, decreased in the presence of added oxalate or chromium (II) ions and when the light intensity was lowered. The gas yield in D2O was appreciably higher than in H2O. The variation of φgas with pH (D) and with added oxalate ion was roughly parallel in the two liquid media. The gas yield increased in the series:A tentative mechanism is suggested to explain the results.

Reactions of Hydrogen and Deuterium Atoms Formed in the Photolysis of Methane and Perdeuterated Methane at 123.6 nm

The photolysis of methane and perdeuterated methane has been carried out at 123.6 nm, in the presence of interceptors (deuterium in the case of methane, and hydrogen in the case of deuterated methane). The hydrogen and deuterium atoms formed are statistically in thermal equilibrium with the reaction medium; it follows that the photodissociation into CH3 and H has a probability close to zero at 123.6 nm. In addition, it is confirmed that CH4 and CD4 have different photolytic behaviors insofar as the quantum yields of hydrogen and deuterium are concerned, with φH > φD.

Strahlenchemie von alkoholen—IX : Die UV-photolyse (λ = 185 nm) von methanol in flüssiger phase

The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H 2) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH 3OD shows, that as in the gasphase 2 the scission of the OH-bond (1) is the major process. CH 3OH + h v (λ = 185 nm) → CH 3O • + H • (1) In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H 2) = 0·42, φ(glycol) = 0·32 and φ(CH 4) = 6 x 10 −4 is obtained. Ethane cannot be detected.

Vacuum-Ultraviolet Photochemistry. VII. Photolysis of Hydrazine at 1236 and 1470 Å

The photolysis of hydrazine vapor has been investigated at 1236 and 1470 Å. At 1236 Å, fluorescence is observed at 3360 Å and is attributed to the NH(A3π→X3Σ−) transition. The emission has been studied as a function of pressure and photolysis time. No emissions were observed at 1470 Å. The products of the photolysis of hydrazine are nitrogen, hydrogen, and ammonia. The pressure dependence of these products has been determined at 1236 and 1470 Å. Formation of the parent ion N2H4+ probably occurs at 1236 Å but not at 1470 Å. At the latter wavelength, reduction of the hydrogen yield upon addition of C2D4 is explained by the reactions: N2H4+hv→N2H3+H,H+N2H4→H2+N2H3.Nitrogen production is not reduced in the presence of C2D4 and the quantum yields of hydrogen and nitrogen are equal under these conditions. These products arise mainly from decomposition of N2H2 (di-imide). The latter may be formed directly from hydrazine, from decomposition of N2H3 or in the disproportionation of N2H3 radicals. Contributions from radical—radical combination reactions are minor based on the relative H2/N2 yields observed in this study and on the lack of mixing of isotopic nitrogen previously reported.

Gas phase photolysis of hydrogen iodide. Part 1.—Inhibition with nitric oxide at 25°C

The photolysis of hydrogen iodide in the presence of nitric oxide has been studied at 25°C (and briefly at 45°C) using the Hg emission at 3130 and 3660 A. Under these conditions nitric oxide was found to act as a simple inhibitor, reducing equally the quantum yields of hydrogen and iodine. A mechanism is proposed involving HNO as an intermediate. The pressure dependence of the reaction H+NO+M→HNO+M is discussed and the results are compared with those of other workers.

The photooxidation of polymers. II. Photolysis of polystyrene

AbstractIn the vacuum photolysis of polystyrene films at 28°C. under 2537 A. radiation the only gaseous product is hydrogen. At the same time the polymer becomes insoluble and discolors. The intensity exponent of the reaction is unity, the quantum yield of hydrogen is 4.3 × 10−2, the overall energy of activation is 2.9 kcal./mole, and the rate of photolysis is independent of molecular weight. No hydrogen is produced when 3650 A. radiation is used. These observations can be interpreted in terms of a simple reaction scheme in which the primary effect of the 2537 A. radiation is to liberate hydrogen atoms. The subsequent reaction of these and the polystyryl radicals simultaneously formed in a number of competing steps results in the appearance of hydrogen, the occurrence of crosslinking, and the production of carbon–carbon unsaturation in the main chain which ultimately leads to conjugation and color. These theories are supported by infrared and ultraviolet spectral measurements and by the observation that the rate of photolysis is accelerated by nitrogen.

Die Bestimmung der Lichtintensität von Niederdruck-Quecksilberlampen bei 1849 Å

Intensities at 1849 Å of various types of low pressure mercury lamps were measured. The values ranged from 1016 to 2·1017 quanta/sec, depending on the type of lamp. The LOSSING type lamp yielded an output of 8·1016 quanta/sec in a 2 cc reaction volume, the largest output per unit volume tested. The intensity of the line at 1849 Å relative to that at 2537 A was measured with a Seya-Namioka grating monochromator. The line at 1849 A was 10 to 15% of that at 2537 A in an electric discharge lamp. In a microwave-operated lamp, the intensity of the former line was 5% of the latter. Ethylene was used as an actinometer to measure the quantum yield at 1849 A. The quantum yields of hydrogen and acetylene from ethylene were 0.8 ± 0.1 and 1.0 ± 0.1, respectively.

Photolysis of cellulose in a vacuum with 2537 A. Light

AbstractCotton sliver, cotton linters, periodate‐chlorite‐oxidized cellulose, and several regenerated celluloses were photolyzed by 2537 A. ultraviolet light in a vacuum at 40°C. The changes in quantum yields of hydrogen, carbon monoxide, carbon dioxide, hydrocarbons, aldehyde groups, carboxyl groups, and chain scissions with respect to quanta of light absorbed and initial functional group concentration indicated that photolysis of alcohol groups plays a dominant role in the complex of interdependent primary and secondary reactions taking place. Periodate‐chlorite‐oxidized cellulose is much more suceptible to photochemical degradation than is unoxidized cellulose. Neutralization with very dilute sodium hydroxide solution reduced the quantum yields of the oxycellulose to values similar to those obtained with the unoxidized material.

Mechanism of the Mercury Photosensitized Decomposition of n-Butane

The results of further studies of the mercury photosensitized reactions at room temperature of n-butane and of its mixtures with nitrous oxide are reported. The importance of a self-scavenging process responsible for low quantum yields of hydrogen at finite conversions has been demonstrated by carrying out experiments at low conversions closely approaching initial conditions. The initial quantum yield of hydrogen has been determined relative to that of nitrogen from the mercury photosensitized decomposition of nitrous oxide. The mechanism of the self-scavenging process is discussed.

Reaction of Diborane with Hg 6(3P1) Atoms

An investigation has been made of the decomposition of diborane, photosensitized by mercury-6(3P1) atoms under static conditions, at 29.30°C. The quantum yields of pressure increase and product formation have been found to be independent of substrate pressure in the complete quenching region. For runs of one hour duration at an incident light intensity of 2.5×10—6 einstein/min, the quantum yields are 0.50±0.02 for hydrogen, 0.25±0.02 for tetraborane, 0.02±0.02 pentaborane and 0.070±0.002 for pressure increase. The mean quantum yields of hydrogen and tetraborane formation were found to decrease with increasing duration of exposure during the first half-hour of irradiation. Constant values were reached after 30–45 min of exposure. The ratio of the rates of hydrogen to tetraborane formation was found to maintain a value of two, independent of substrate pressure and duration of exposure, for runs exceeding five minutes in duration. Extensive decomposition was found to lead to solid products. A mechanism is proposed involving the primary scission of the B–H bond which accounts qualitatively for the observed characteristics of the reaction. The resemblance between ethane and diborane with respect to their behavior toward Hg 6(3P1) atoms is pointed out.

Mercury Photosensitized Reactions of Propane

An investigation has been made of the mercury photosensitized reactions of propane, alone and in the presence of hydrogen at temperatures from 25 to 323°C. The products of the reaction are predominantly hydrogen, hexanes (mainly 2,3-di-Me-butane and 2-Me-pentane), and a small amount of higher paraffins. The postulated mechanism is: Hg(3P1)+C3H8→Hg(1S0)+C3H7+HHg(3P1)+H2→Hg(1S0)+2HH+C3H8→C3H7+H22C3H7→C6H142H→H2C3H7+C3H8→C6H14+H.The quantum yield of hydrogen is approximately 0.15 at 25°C and rises somewhat with increasing temperature.