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Mercury atoms were excited to the 6 3P1 state with a pulsed laser and a lamp at 253.7 nm in the presence of H2, D2, HD, and mixtures of these gases. The hydrogen atom reaction products were detected by vacuum ultraviolet (VUV) laser induced fluorescence. The ratio of yields of the two body channel (mercury hydride and a hydrogen atom) and the three body channel [Hg(6 1S0) and two hydrogen atoms] were determined by combining the H/D atom ratios and a literature value of the HgD/HgH ratio from reaction with HD. Assuming that the sum of the two yields is unity, the yield of the two body channel is for H2 0.63±0.15, for D2 0.79±0.11, and for HD 0.10±0.02 (HgH+D) and 0.65±0.03 (HgD+H). The average kinetic energies calculated by combining these yields with the literature data on internal energy release in the mercury hydride molecules agree with the average kinetic energies measured from the Doppler broadened fluorescence excitation curves. When the E vector of the exciting polarized light was rotated there was no effect on the hydrogen atom spectrum proving that the hydrogen atom velocity distribution is isotropic. When the mercury atoms were excited with circularly polarized light to the J=1, MJ=1 state, the hydrogen atoms exhibited no spin polarization. Electron spin resonance (ESR) signals observed when irradiating a mixture of Hg and hydrogen molecules were shown by isotopic effects to be due to hydrogen atoms dissociated from mercury hydride molecules. [ABSTRACT FROM AUTHOR]

The photodissociation of ethylene at 193 nm is studied by laser induced fluorescence of the hydrogen atom product. The quantum yield for producing deuterium atoms from C2D4 is 0.19±0.04. Their average translational energy is 7.3±1.3 and 15.1±1.4 kcal/mol at 193 and 157 nm, respectively. Considerable evidence, both experimental and theoretical, shows that dissociation takes place from a hot internally equilibrated ground state molecule. A remarkable isotope effect is found. The ratio of H atoms to D atoms released from CH2CD2 is 2.2±0.2, whereas that from t-CHDCHD is 1.2±0.1. An RRKM model explains these ratios. For CH2CD2 the vibrational frequencies of the transition state for releasing H atoms are quite different from those for the release of D atoms. In t-CHDCHD, the transition state frequencies are nearly the same; there is a cancellation between differing zero point energies and moments of inertia. [ABSTRACT FROM AUTHOR]

The exchange reaction H(1 eV)+RD→RH+D, where RD was deuterated acetylene, methylacetylene, ethylene, and propylene was studied by laser induced fluorescence detection of the hydrogen and deuterium atoms. The reaction cross sections were 1.69±0.22, 0.50±0.15, 1.85±0.20, and 1.10±0.14 Å2, respectively. The fraction of the incident relative kinetic energy released as translation was 0.42, 0.34, 0.40, and 0.34. That the addition of a methyl group only slightly reduces the energy released as translation is regarded as proof that the reaction at this energy does not involve a long lived intermediate complex, but is a direct localized displacement. Further confirmation comes from the observation that the velocity of the D atom product of H+C2D2 is correlated with the velocity of the H atom reactant. [ABSTRACT FROM AUTHOR]

When energized sufficiently either vibrationally or electronically, ROH (where R is methyl or ethyl) can dissociate to form H atoms and RO radicals. We have determined the translational energy release (=0.82Eavl ) and angular distribution (β=-0.60±0.03) from the laser induced fluorescence spectra of H atoms produced in the 193 nm photodissociation of CD3OH. We have also determined that the quantum yield for producing H from CD3OH is 0.86±0.10. In contrast, the reaction of O(1D)+CH4 which produces vibrationally excited CH3OH, has a quantum yield for producing H atoms of roughly 0.25 with only 22% of the available energy released as translation. We conclude that although the total available energy is the same in both cases, the dissociation of photoexcited methanol is prompt whereas the dissociation of chemically activated methanol shows some degree of internal vibrational equilibration. [ABSTRACT FROM AUTHOR]

Alkyl chlorides (R=CH3, C2H5, C3H7, and C4H9), chloromethanes (CHnCl4-n), and chlorofluoromethanes (CFnCl4–n) are photodissociated at 157 and 193 nm. The chlorine atom photofragments are detected by a resonance enhanced multiphoton ionization technique. The branching ratios of the Cl photofragments [Cl*(3p2P1/2)]/[Cl(3p2P3/2)] are almost identical (0.23±0.03) for alkyl monochlorides at 157 and 193 nm and for CH2Cl2 and CHCl3 at 157 nm, while the ratios are rather small (0.10±0.02) for CH2Cl2 and CHCl3 at 193 nm. No discernible isotope effects on the branching ratios were observed when D atoms were substituted for H atoms in chloromethanes. For CCl4, CF3Cl, CF2Cl2, CFCl3 at 157 and 193 nm, the ratios are small (<0.05) irrespective of the number of Cl atoms in the parent molecules. The Doppler profiles of the chlorine photofragments have been obtained and it is found that (a) CF3Cl undergoes a perpendicular optical transition at 157 nm and (b) for halomethanes containing more than two Cl atoms, the Cl photofragment has a Boltzmann distribution in translational energy and an isotropic angular distribution. [ABSTRACT FROM AUTHOR]

The article discusses the aspects which drive the development and deployment of hydrogen fuel cell technologies. Topics mentioned include the commercialization of fuel cells through government and industry programs, capability of fuel cells to generate power at high efficiencies with low emissions, as well as the need to reduce emissions of carbon, pollutants, and dependence to petroleum.

Experimental values for the absorption coefficient and the branching ratio of HDO at 157.5 nm are reported. The experimental evidence strongly supports the analysis of Zhang et al. (ref.10).(AIP) [ABSTRACT FROM AUTHOR]