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  • 2000-2004  (14)
  • 1995-1999  (14)
  • 1970-1974  (2)
  • 1965-1969  (4)
  • 1960-1964  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Time-resolved dissociative intense-laser field ionization for probing dynamics: Femtosecond photochemical ring opening of 1,3-cyclohexadiene (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8347-8362 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The concerted photochemical ring opening of 1,3-cyclohexadiene was investigated in the gas phase by low-intensity pumping at 267 nm and subsequent probing by high-intensity photoionization at 800 nm and mass-selective detection of the ion yields. We found five different time constants which can be assigned to traveling times along consecutive parts of the potential energy surfaces. The molecule is first accelerated in the spectroscopic state 1B along Franck–Condon active coordinates, then alters direction before changing over to the dark state 2A. All constants including that for leaving the 2A surface are below 100 fs. These times are shorter than appropriate vibrational periods. Such a maximum speed is evidence that the pathway is continuous leading from surface to surface via real crossings (conical intersections) and that the molecule is accelerated right into the outlet of the 2A/1A funnel. On the ground state it arrives as a compact wave packet, indicating a certain degree of coherence. The experimental method promises a high potential for investigating dynamics, since many consecutive phases of the process can be detected. This is because the fragmentation pattern depends on the location on the potential energy surface, so that monitoring several different ions permits to conclude on the population flow through these locations. Ionization at the intensities used is normally considered to be an effect of the electric field of the radiation. But in our case it is enhanced by resonances in the neutral molecule and in particular in the singly positive ion, and it is not sensitive for the length of the molecule (different conformers of the product hexatriene). The ionic resonances explain why hexatriene has a much richer fragmentation pattern than cyclohexadiene. Coulomb explosion is observed from an excited state of a doubly positive ion. Its mechanism is discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481478
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  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond photochemical ring opening of 1,3-cyclohexadiene studied by time-resolved intense-field ionization (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9386-9389 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474009
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  • 3
    Electronic Resource
    Electronic Resource
    Untersuchungen zur Phylogenetik der Pseudocholinesterasen (1964)
    Springer
    Human genetics 〈Berlin〉 1 (1964), S. 126-140 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389629
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  • 4
    Electronic Resource
    Electronic Resource
    Über die Verwendung des Pseudocholinesterase-Polymorphismus im Paternitätsgutachten (1965)
    Springer
    Human genetics 〈Berlin〉 1 (1965), S. 311-318 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Pseudocholinesterase-Varianten können heute ohne großen Aufwand routinemäßig bestimmt werden. Es wurde deshalb die Frage geprüft, ob dieser Polymorphismus in der Paternitätsbegutachtung verwendet werden kann. Wegen der ungünstigen Genverteilung ist nur in sehr wenigen Fällen eine zusätzliche Information zu erwarten. Stimmen Kind und fraglicher Vater indessen in einer seltenen Variante überein, so ist der Hinweiswert sehr hoch (Essen-Möller-Ansatz). Die Chance, von der Vaterschaft ausgeschlossen zu werden, liegt für zu Unrecht bezichtigte Männer bei etwa 1,5%. Dazu werden eigene Untersuchungen mitgeteilt.
    Notes: Abstract Today, pseudocholine-esterase variants can be routinely differentiated without very specialized technical equipment. Therefore this well known polymorphism should be taken into consideration in paternity cases. In view of the distribution of gene frequencies, however, additional information is to be expected in very few cases only. If child and suspected father have a rare variant in common the likelihood for this man to be the father is very high (Essen-Möller's formula). The chance for wrongly accused men to be excluded is in the range of 1,5%. Some own observations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273972
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  • 5
    Electronic Resource
    Electronic Resource
    Weitere Untersuchungen zur Phylogenetik der Pseudocholinesterasen (1966)
    Springer
    Human genetics 〈Berlin〉 2 (1966), S. 42-51 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285909
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  • 6
    Electronic Resource
    Electronic Resource
    Isotope-selective IR multiphoton dissociation of CHClF2 in the presence of NO2 (1997)
    Springer
    Applied physics 65 (1997), S. 577-582 
    Details
    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
    URL: http://dx.doi.org/10.1007/s003400050316
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  • 7
    Electronic Resource
    Electronic Resource
    Macroscopic enrichment of12C by a high-power mechanically Q-switched CO2 laser (1996)
    Springer
    Applied physics 62 (1996), S. 329-332 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01081193
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  • 8
    Electronic Resource
    Electronic Resource
    Pulsed infrared selective dissociation of CF3Br as a function of pressure, temperature, fluence and wavelength (1996)
    Springer
    Applied physics 63 (1996), S. 51-56 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01112838
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  • 9
    Electronic Resource
    Electronic Resource
    Isotopically selective IR multiphoton dissociation of 1,3,5-trioxane (1996)
    Springer
    Applied physics 62 (1996), S. 203-212 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01081126
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  • 10
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    Femtosecond Dynamics of Fe(CO)5Photodissociation at 267 nm Studied by Transient Ionization (2000)
    American Chemical Society
    Details
    Publication Date: 2000-03-01
    Print ISSN: 1089-5639
    Electronic ISSN: 1520-5215
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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