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  • 1995-1999  (5)
  • 1960-1964  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Human genetics 〈Berlin〉 1 (1964), S. 126-140 
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0649
    Keywords: 82.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The pulsed InfraRed (IR) photodissociation of pure CF3Br and a 1:3 mixture with H2 has been studied as a function of pressure, temperature, fluence and wavelength. The results have been obtained by mass spectrometry. Maximum enrichment for carbon 13 is obtained when irradiating with the 1046.9 cm−1 (9P20) line, but the selectivity is stronger at longer wavelengths. The enrichment factor tends towards 1 when pressure increases with the pure substance, but it is less affected in the mixture. It seems that hydrogen has a buffer effect. The selectivity shows maxima for all lines with the fluence and increases when the temperature is decreased from 22 to − 85°C. Some enrichment is observed for the bromine 79 isotope when irradiating with 1046.9 cm−1 (9P20).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0649
    Keywords: PACS: 82.40Z; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 2 to the CHClF2/He mixture irradiated by a Q-switched CO2 laser leads to oxidation of the dissociation product according to the reaction: CF2+NO2→COF2+NO. The resulting COF2 with a 13C content near 50% is easy to convert to CO2 or CO for further enrichment by a nonlaser process. We measured the dependence of the fraction of dimerised CF2 on NO2 pressure pNO2 and the amount of NO2 required to suppress dimerisation on the dissociation yield. Both agree with a kinetic model using known rate constants. For the range of the dissociation parameters (13CF2 yield of 10% per pulse, isotope selectivity of 130) of practical interest, 95% of the CF2 produced is oxidized at pNO2≈1/2pCHClF2. In the absence of NO2, major (20%–35%) losses of CF2 at the metal walls of the irradiation system were observed. Addition of NO2 suppresses them. For comparison, we also used O2 as a scavenger in CHClF2 dissociation. NO2 is by orders of magnitude more efficient.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0649
    Keywords: 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The isotope-selective multiphoton dissociation of CHClF2 in a multipass refocusing Herriott cell was used to enrich more than 4 moles of chlorodifluoromethane to 99.99% of12C isotopic purity. It is the largest isotope quantity ever separated by a laser process. A cw excited mechanically Q-switched CO2 laser, which delivers 16 mJ pulses at 5 kHz was used. The enrichment controlled by a mass-spectrometer and guided by a PC was run with a rate of 25 g12C per 24 h.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 62 (1996), S. 203-212 
    ISSN: 1432-0649
    Keywords: 33.80.Wz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Searching for oxygen-isotope selectivity, we investigated the infrared multiphoton dissociation of the formaldehyde trimer around 10 µm, in a range where the molecule has a degenerate and a non-degenerate CO stretch vibration and a degenerate CH2 deformation vibration. In the region of the two latter, the wavelength dependence of the dissociation yield exhibits sharp structures. They were assigned ton-photon resonances (n = 2, 3, 5) by the help of the IR spectrum in the fundamental and overtone region. The O and C selectivities were very small (1.05) near the non-degenerate CO stretch band, but surprisingly large (2–4) in the CH2 deformation, which has no isotopic shift. The selectivity is not controlled by the first (n-photon) excitation step, but only by a later step. Its assignment is attempted. The pressure dependence of the dissociation is peculiar: Only after an initial decrease, the yield exhibits the usual rise with pressure. We attribute the decrease to a relaxation which perturbs the two-photon resonance.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We found that hydrogen ion formation due to multielectron dissociative ionization by an intense-laser field is much less efficient with 1,3-cyclohexadiene than with its isomer 1,3Z,5-hexatriene (Z-HT). Moreover by suppressing the ionization barrier an intense-laser field ejects electrons most efficiently from molecular states of low ionization potential. After pumping 1,3-cyclohexadiene at 267 nm to its 1B2 state we probe the system by intense-laser field ionization with delayed 800 nm pulses. Monitoring of the parent ion C6H8+, of the main fragment C6H7+ and of H+ allows us to follow the motion from the 1B2 surface to the dark 2A1 state and from there towards the 2A1/1A1 conical intersection to the ground-state surface of the product. The measured 1B2 and 2A1 lifetimes are 43±3 and 77±7 fs, respectively, and the primary photoproduct cZc-HT is produced within 200 fs. © 1997 American Institute of Physics.
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