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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4784-4789 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction of two narrow band (Δν〈100 MHz) UV light pulses of different intensity with a molecular three-level system is investigated experimentally. The laser frequencies are tuned to an up (pump) and a down (dump) transition sharing a common excited rovibronic S1 level whose population is probed by a transition to the ionization continuum and ion detection. The time sequence of the two pulses results either in a lambda type coherent stimulated Raman adiabatic passage or a stimulated emission pumping (SEP) process. When the first case is realized by a 6.4 ns delay of the low intensity pump laser from the high intensity dump laser pulse, a fourfold increase of the depth of the ion dips compared to the SEP experiment is observed. This is in line with numerical calculations of the level populations using a density matrix formalism including coherent effects. Rotationally resolved ion dip spectra of the 62 state of benzene are presented and demonstrate the high sensitivity of the coherent excitation process of this work for ion dip spectroscopy.
    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 102 (1995), S. 3055-3063 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The van der Waals (vdW) vibronic spectrum built on the electronic 000, S1(B2)←S0(A1) origin of p-difluorobenzene–Ar is investigated with rotational resolution (ΔνUV=60 MHz). For the first time vdW vibronic bands are detected up to a van der Waals energy of 125 cm−1 and assigned by a rotational analysis of the band structure. The band origin positions of the ten detected bands display a regular behavior with moderate anharmonicities and minor influences due to Fermi resonances. Using the concept of three-dimensional Kraitchman equations and of normalized effective planar moments characteristic data on the nuclear displacements in the two different bending coordinates are deduced from the measured rotational constants. The fundamental vdW vibronic states at low energies can be described in terms of one-dimensional normal modes while vdW states at higher energies display mixed mode character. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9257-9261 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the high-resolution UV spectrum of the 000(S1←S0) transition in fluorene–(Ar)2 recorded by mass-selective resonance-enhanced two-photon ionization with a pulsed narrow-band laser system (Δν=140 MHz). The measured b-type rotational structure of the strongest band at 33 692.51 cm−1 in fluorene–(Ar)2 allows the exclusion of a (2||0) structure for this band with the two Ar atoms placed on one side of the substrate. The observation of a b-type rotational transition is proof of a specific opposite sided (1||1) structure with the two Ar atoms placed above (and below) the central five-membered ring and one remaining sign ambiguity concerning the short in-plane axis coordinate. © 1994 American Institute of 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 104 (1996), S. 865-881 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotationally resolved vibronic spectra of eight van der Waals bands built onto the 610 transition of the bare molecule are reported for the complexes C6H6⋅Ar, C6D6⋅Ar, and C6H6⋅84Kr. The rotational structure of most of the bands is identified as that of a perpendicular transition with Coriolis coupling constants nearly the same as those of the 610 band of the respective complex. We therefore conclude that the excited van der Waals modes of the three complexes have a1 symmetry. Precise rotational constants are fitted to the large number of unblended lines assigned in each spectrum. In contrast, the lowest energy van der Waals bands of both C6H6⋅Ar and C6D6⋅Ar display a completely different rotational structure which can neither be explained by a genuine perpendicular nor a genuine parallel transition. This situation will be analyzed in detail in accompanying work and the final vibronic assignments deduced. The rovibronic lines in all the spectra show a linewidth of 130 MHz that is solely due to the laser linewidth and to residual Doppler broadening in the molecular jet. It is concluded that the excited vibronic combination states of intramolecular and van der Waals vibrations do not predissociate on the nanosecond time scale of our experiment. Two of the reported spectra show irregularities in the rotational structure that are explained by coupling to adjacent combination states. © 1996 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 103 (1995), S. 3315-3324 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent ion dip spectroscopy (CIS) provides high sensitivity and high resolution for the investigation of vibrational overtones in molecular electronic ground states. For a special time sequence of two coherent narrow-band Fourier transform limited nanosecond UV light pulses, with a modest delay of the pump pulse of 6.4 ns, a complete blocking of the population transfer to the upper state is achieved in the lambda-type three-level system ion dip experiment. This leads to ion dips with a depth as large as 95% and each dip represents an individual rovibronic transition. In this work, CIS is applied for the first time to a weakly bound van der Waals complex, benzene–Ar. We are able to observe six new van der Waals vibrational states up to an excess energy of 130 cm−1. The assignments are made by comparison with recent S1 excited state data of benzene–Ar and p-difluorobenzene–Ar and by analysis of the positions and intensities of the observed individual rotational lines. The frequency positions of the intermolecular vibrational states display a regular pattern up to 130 cm−1. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica A: Statistical Mechanics and its Applications 156 (1989), S. 114-129 
    ISSN: 0378-4371
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Vacuum 36 (1986), S. 47-49 
    ISSN: 0042-207X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2015-05-15
    Description: 4-Nerolidylcatechol ( 1 ) is an abundant antiplasmodial metabolite that is isolated from Piper peltatum roots. O -Acylation or O -alkylation of compound 1 provides derivatives exhibiting improved stability and significant in vitro antiplasmodial activity. The aim of this work was to study the in vitro inhibition of hemozoin formation, inhibition of isoprenoid biosynthesis in Plasmodium falciparum cultures, and in vivo antimalarial activity of several 4-nerolidylcatechol derivatives. 1,2- O , O -Diacetyl-4-nerolidylcatechol ( 2 ) inhibited in vitro hemozoin formation by up to 50%. In metabolic labeling studies using [1-( n )- 3 H]geranylgeranyl pyrophosphate, diester 2 significantly inhibited the biosynthesis of isoprenoid metabolites ubiquinone 8 , menaquinone 4 , and dolichol 12 in cultures of P. falciparum 3D7. Similarly, 2- O -benzyl-4-nerolidylcatechol ( 3 ) significantly inhibited the biosynthesis of dolichol 12 . P. falciparum in vitro protein synthesis was not affected by compounds 2 or 3 . At oral doses of 50 mg per kg of body weight per day, compound 2 suppressed Plasmodium berghei NK65 in infected BALB/c mice by 44%. This in vivo result for derivative 2 represents marked improvement over that obtained previously for natural product 1 . Compound 2 was not detected in mouse blood 1 h after oral ingestion or in mixtures with mouse blood/blood plasma in vitro . However, it was detected after in vitro contact with human blood or blood plasma. Derivatives of 4-nerolidylcatechol exhibit parasite-specific modes of action, such as inhibition of isoprenoid biosynthesis and inhibition of hemozoin formation, and they therefore merit further investigation for their antimalarial potential.
    Print ISSN: 0066-4804
    Electronic ISSN: 1098-6596
    Topics: Biology , Medicine
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  • 9
    Publication Date: 2019-07-17
    Description: Long-term time series of hydrogen chloride (HCl) and chlorine nitrate(ClONO2) total column abundances have been retrieved from high spectralresolution ground-based solar absorption spectra recorded withinfrared Fourier transform spectrometers at nine NDSC(Network for the Detection of Stratospheric Change) sites in bothNorthern and Southern Hemispheres. The data sets span up to 24years and most extend until the end of 2001. The time series ofCly (defined here as the sum of the HCl and ClONO2 columns) from thethree locations with the longest time span records show rapid increasesuntil the early 1990s superimposed on marked day-to-day, seasonal andinter-annual variability. Subsequently, the buildup in Cly slowsand reaches a broad plateau after 1996, also characterized byvariability. A similar time evolution is also found in the totalchlorine concentration at 55 km altitude derived fromHalogen Occultation Experiment (HALOE) global observations since 1991.The stabilization of inorganic chlorine observed in both the totalcolumns and at 55 km altitude indicates that the near-global 1993organic chlorine (CCly) peak at the Earth?s surface has now propagatedover a broad altitude range in the upper atmosphere, though the timelag is difficult to quantify precisely from the current data sets dueto variability. We compare the three longest measured time serieswith two-dimensional model calculations extending from 1977 to 2010,based on a halocarbon scenario that assumes past measured trendsand a realistic extrapolation into the future.The model predicts broad Cly maxima consistent with the long-termobservations, followed by a slow Cly decline of 12-14% relative to thepeak by 2010. The data reported here confirm the effectiveness of theMontreal Protocol and its Amendments and Adjustments in progressivelyphasing out the major man-related perturbations of the stratosphericozone layer, in particular, the anthropogenic chlorine-bearing source gases.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
    Publication Date: 2019-07-17
    Description: This paper presents extensive {bias determination} analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from nearly 20 satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the average values of the mean relative differences are nearly all within +1 to +8%. At higher altitudes (4560 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments, with mean relative differences of up to +40% (about +20% on average). For the ACE-MAESTRO version 1.2 ozone data product, mean relative differences are within ±10% (average values within ±6%) between 18 and 40 km for both the sunrise and sunset measurements. At higher altitudes (~3555 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (with mean relative differences down to −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS, indicating a large positive bias (mean relative differences within +10 to +30%) in the 4555 km altitude range. In contrast, there is no significant systematic difference in bias found for the ACE-FTS sunrise and sunset measurements.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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