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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 9361-9369 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports an experimental study of the photolysis of aqueous HOCl using femtosecond pulses at 266 nm. The formation of photoproducts is monitored by transient absorption spectroscopy from 230 to 400 nm. The HOCl molecules dissociate with unity quantum yield to form OH+Cl faster than 1 ps, and as a result of the potential along the HO–Cl reaction coordinate, all excess energy is given to the fragments as translational energy. After dissociation, and solvent cage escape, the majority of the Cl and OH fragments recombine after diffusion on a time scale of 50 ps. The diffusion dynamics is studied using a simple model for diffusive recombination and a more extensive molecular dynamics simulation. A minor fraction of the Cl atoms (∼10%) reacts with HOCl in a diffusion limited reaction to form Cl2+OH. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1126-1134 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultrafast solvation and recombination dynamics of the hydrated electron generated by two-photon ionization of water at 4.65 eV is studied by transient absorption spectroscopy as a function of temperature in the range from 277 K to 355 K. The part of the spectral blue shift which is observed in the absorption spectrum of the hydrated electron after 1 ps is purely continuous and is accurately described by the well known analytical expression for the temperature dependent absorption spectrum of the ground state hydrated electron. This indicates that thermal relaxation or more likely solvation of the hydrated electron predominantly causes the blue shift. The survival probability of the hydrated electron shows a strong temperature dependence, which is satisfactory explained by the temperature dependent mobility and reaction rates of the species involved in the recombination. This implies that the average initial separation between the hydrated electron and the ionization site of 〈r0〉=1.0±0.1 nm does not depend significantly on the bulk water temperature. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section A 143 (1970), S. 213-224 
    ISSN: 0375-9474
    Keywords: Nuclear reactions
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 703-710 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photolysis of aqueous CS2 has been studied using subpicosecond transient absorption spectroscopy. CS2 was photolyzed at 6.2 eV and the fast formation and decay of the photoproducts were monitored from 6.2 to 3.96 eV. Upon excitation, aqueous CS2 dissociates into CS+S. However, 93%±2% of the fragments geminately recombine on the electronic ground state potential of CS2 within a few picosecond leaving only 7%±2% of the CS+S fragments separated 100 ps after the excitation. In the gas phase, most of the dissociation occurs on a triplet-state potential surface, and the high recombination yield observed in aqueous solution therefore indicates a strong, solvent-assisted coupling between this state and the singlet ground state of CS2. The vibrationally excited CS2 molecule formed by the recombination transfers its high excess energy to the surrounding water molecules in two processes with time constants 8.4±1 and 33±7 ps. The rotational reorientation time of ground state CS2 is 6±1 ps, suggesting a surprisingly strong interaction between the neutral, nonpolar CS2 and the surrounding water molecules. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5874-5893 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The intermediate vibrational energy regime—well above the zero point, yet below the first dissociation limit—plays an important role in many molecular processes, such as radiationless transitions or intramolecular vibrational energy redistribution (IVR). For molecules with N〉6 vibrational degrees of freedom, the calculation of energy levels and spectra of the full anharmonic vibrational Hamiltonian at high energies presents a formidable problem. Here we derive an asymptotic factorization of the potential energy surface (PES) based on the global topography of molecular potentials. The resulting approximate models require only a few input parameters such as vibrational frequencies and cubic anharmonicities. They are compared to benchmark PES derived from curvilinear model potentials and Monte Carlo sampled ab initio calculations for several small molecules. Higher order couplings are found to make a significant contribution to IVR decays at long times. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3453-3462 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation and photoionization of liquid water following two-photon absorption at 266 nm is studied in the spectral range from 213 to 1108 nm with subpicosecond time resolution. Probing in the UV enables the first direct simultaneous observation of the photoproducts eaq−, Haq, and OHaq. This makes it possible to follow the geminate recombination kinetics between the photoproducts and to determine the relative yields of the dissociation and ionization channels. The concentration of hydrated electrons deduced from the visible and near-infrared transient absorption measurements decays by 40%±2% within the first 90 ps due to recombination with OHaq and H3O+. Analyzing our measurements of the hydrated electron concentration using the independent reaction time approximation results in the relative yields of 82%±3% and 18%±3% for recombination with OHaq and with H3O+, respectively. This is in excellent agreement with the relative yield of 82%±10% for recombination with OHaq determined directly from our ultraviolet transient absorption measurements. The contribution of hydrated electrons from direct ionization is insignificant when liquid water is excited below 9.32 eV and the ionization is likely to occur via dissociation and proton transfer. The transient ultraviolet absorption data shows that if ionization exclusively occurs via dissociation, 65% of the produced H(hot) atoms react with the surrounding solvent molecules to produce hydrated electrons. If proton transfer, on the other hand, is the only process responsible for the ionization, our measurements show that the ratio between dissociation and ionization is 55%. Geminate recombination of OHaq and Haq fragments following the photodissociation at 9.32 eV is not observed indicating that the translation energy of at least one of the fragments is sufficient to penetrate the water solvent cage. Finally, we have measured the two-photon absorption spectrum of liquid water from 110 to 160 nm, and the spectrum is in good agreement with our ab initio gas-phase calculations of the two-photon absorption cross sections for the transitions involved. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 1507-1511 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Sediment cores up to 6.5 m in length from the South Arm of Great Salt Lake, Utah, have been correlated. Radiocarbon ages and volcanic tephra layers indicate a record of greater than 30,000 years. A variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation; these include acoustic stratigraphy, sedimentologic analyses, mineralogy, geochemistry (major element, C, O and S isotopes, and organics), paleontology and pollen. The results indicate that prior to 32,000 year B.P. an ephemeral saline lake-playa system was present in the basin. The perennial lake, which has occupied the basin since this time, rose in a series of three major steps; the freshest water conditions and presumably highest altitude was reached at about 17,000 year B.P. The lake remained fresh for a brief period, followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present Great Salt Lake. The lake remained at low elevations, and divided at times into a north and south Basin, until about 8,000 year B.P. Since that time, with the exception of two short rises to about 1290 m, the lake level has remained near the present elevation of 1280 m.
    Type of Medium: Electronic Resource
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