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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2257-2266 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally excited levels of the a 4Π state, the lowest electronically excited state of the NO molecule, can be studied through their collisional energy transfer to the radiating B 2Π state. Following one-photon excitation in the 11–0 band of the forbidden a 4Π–X 2Π transition with the output of a tunable dye laser, we monitor the temporal evolution of the emission from the v=2 level of the B 2Π state. From pressure-dependence analysis, we determine the removal rate coefficients for a 4Π(v=11) with NO, O2, N2O, N2, CO2, He, and Ar. In addition, using direct B 2Π excitation of the v=2, 3, 4 levels, we obtain removal rate coefficients for the same colliders. These vibrational levels span the region around a 4Π(v=11). In general, a 4Π removal is quite fast, ranging from rate coefficients of 1.0×10−12 cm3 s−1 to more than 1.0×10−10 cm3 s−1, and is substantially faster than B 2Π removal for N2, N2O, CO2, and Ar. NO(B 2Π, v=3) removal is generally much faster than that for the v=2 and v=4 levels, because of a localized perturbation between the v=12 level of the a 4Π state and v=3 of the B 2Π state. Preliminary measurements on transfer between the b 4Σ− and B 2Π states are reported. © 1997 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2249-2256 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Improved spectroscopic measurements have been made on the NO(a 4Πi–X 2Πr) 11–0 band, and new measurements on the 14–0 band, bringing the explored region of the a 4Π state to within 0.3 eV of the NO dissociation limit. Doubling and mixing of dye laser radiation is used to access the 200–210 nm region with an ultraviolet linewidth of 0.15 cm−1. The a 4Π molecules collisionally convert their energy to the B 2Π state, from which radiation is detected. Almost 300 lines have been observed in each of the two bands, and accurate spectroscopic constants are presented. New information is provided on the relative positioning of perturbed levels in the a 4Π and B 2Π states. © 1997 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7295-7303 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transversely excited atmospheric pressure CO2 and modulated continuous-wave CO2 laser marking of soda-lime and borosilicate glasses has been investigated as a function of laser fluence and pulse duration. Marks are formed by a combination of surface crazing and material removal, the latter occurring predominantly through particles that are fractured from the surface. Various possible fracture mechanisms are analyzed and residual surface stress following rapid laser heating is identified as the most likely cause of microcracking. Scanning electron microscope studies show that relatively large fragments are produced, with a characteristic thickness that is dependent on the laser pulse duration, but that they predominantly remain locked in the surface. Gas phase products evolved during the interaction have also been subject to evaluation using spectroscopy of the luminous plume and fast photography techniques. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8906-8913 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differential scanning calorimetry, Raman scattering, optical absorption, and upconversion of infrared to green luminescence have been studied for Er3+-doped lead-germanate glass 55GeO2⋅20PbO⋅10BaO⋅10ZnO⋅5K2O (GPBZK) and lead-tellurium-germanate glass 30GeO2⋅30PbO⋅30TeO2⋅10CaO (GPTC). Judd–Ofelt intensity parameters of Er3+ in the two host glasses were determined and used to calculate radiative transition rates and lifetimes. Values of the radiative quantum yield of the 4S3/2→4I15/2 transition and the infrared (797 nm) to green (547 nm) upconversion efficiency of Er3+ were obtained. It has been found that the 4S3/2→4I15/2 radiative transition rate of Er3+ in GPTC glass is about twice that in the GPBZK glass and the upconversion efficiency in the GPTC glass is about four times larger than that in the GPBZK glass. These host-dependent properties are mainly attributed to the enhanced local field and the reduced multiphonon rate in lead-tellurium-germanate glass compared to lead-germanate glass. © 1996 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7809-7815 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: OH collisional removal rate constants for υ=8, 10, and 11 with O2, N2, CO2, N2O, and He are measured. Vibrationally excited OH molecules in υ=5, 7, and 8 are prepared from the reaction of atomic hydrogen with ozone, and selectively excited to υ=8, 10, and 11, respectively, with a pulsed infrared laser via direct overtone excitation. Subsequent collisional deactivation of these laser-populated levels is probed as a function of collider gas partial pressure using a time-delayed, pulsed ultraviolet laser resonant with OH(B 2Σ+−X 2Π) transitions. Fluorescence from OH(B 2Σ+−A 2Σ+) is detected. These results complete a series of removal rate constant measurements for OH(X 2Π) up to υ=12. Resonance enhancement effects in vibration-to-vibration energy transfer for CO2 and N2O factor significantly in the vibrational-level-dependent rate constants. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5798-5802 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional removal rate constants for the OH (X 2Π,ν=7) radical are measured for the colliders O2, CO2, and N2O, and an upper limit is established for N2. OH(ν=4) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to ν=7 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the ν=7 population is probed as a function of the collider gas partial pressure by a time-delayed pulsed ultraviolet laser. The probe laser light is resonant with the (0,7) band of the B 2Σ+−X 2Π transition. Fluorescence from the B 2Σ+ state is detected in the visible spectral region. We measure rate constants for CO2, (6.7±1.0)×10−11; N2O, (3.0±0.6)×10−11; O2, (7±2)×10−12; and N2, 〈6×10−13 (all in units of cm3 s−1). © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    R & D management 18 (1988), S. 0 
    ISSN: 1467-9310
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    R & D management 18 (1988), S. 0 
    ISSN: 1467-9310
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2608-2612 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple pyroelectric detector has been constructed and used to measure the ablation velocity for various polymers as a function of laser (248 nm) fluence. The advantage of this approach over other techniques is that a full sampling of the products in the ablation plume is obtained. Results for polymethyl methacrylate (PMMA) ablation can be interpreted in terms of a single explosive decomposition process in which numerous small fragments such as C2, CO, and CO2 propel small segments of the polymer at velocities which are scaled to the square root of their molecular weights. Data for polymide suggest that this polymer is decomposed by laser photons principally into small molecules. The solid carbon that is obtained on ablation in air is probably derived by reactions between carbon clusters. This technique is suitable for the study of the angular distribution of the ejected material which is useful for modeling and in schemes for the deposition of material by laser ablation.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3820-3822 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A modified Krätschmer–Huffman reactor for the mass production of fullerenes is presented. Fullerene mass production is fundamental for the synthesis of higher and endohedral fullerenes. The reactor employs mechanisms for continuous graphite-rod feeding and in situ slag removal. Soot collects into a Soxhlet extraction thimble which serves as a fore-line vacuum pump filter, thereby easing fullerene separation from soot. Thermal gravimetric analysis (TGA) for yield determination is reported. This TGA method is faster and uses smaller samples than Soxhlet extraction methods which rely on aromatic solvents. Production of 10 g of soot per hour is readily achieved utilizing this reactor. Fullerene yields of 20% are attained routinely. © 1994 American Institute of Physics.
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