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  • 1
    Digitale Medien
    Digitale Medien
    A femtosecond midinfrared pump–probe study of hydrogen-bonding in ethanol (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1483-1490 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present a femtosecond midinfrared pump–probe study of hydrogen bonding. It is shown that upon excitation of the OH-stretching vibration of hydrogen-bonded ethanol dissolved in CCl4, the hydrogen bonds are predissociated on a femtosecond time scale. The measured predissociation time constant depends strongly on the excitation frequency, and ranged from ∼250 fs at 3330 cm−1 to ∼900 fs at 3450 cm−1. The time constant of the subsequent reassociation of the hydrogen bonds was found to be 15 ps, in accordance with previous picosecond studies. Furthermore, polarization-resolved measurements show that orientational relaxation takes place on a time scale much shorter than the pulse length of ∼200 fs. This rapid orientational relaxation can be explained from the fast delocalization of the O–H stretching excitation over the hydrogen-bonded ethanol oligomers. The orientational anisotropy R reaches a value of 0.15 instantaneously, and remains constant for all delays. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.474501
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  • 2
    Digitale Medien
    Digitale Medien
    Atomic disorder and phase transformation in L12-Ni3Al by mechanical milling (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3438-3444 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Mechanical milling of the ordered L12-Ni3Al was performed in a high-energy ball mill. The milling process was monitored by x-ray diffraction, high-field magnetization, ac magnetic susceptibility, and differential scanning calorimetry (DSC). It was found that antisite disorder is generated in the early stages of milling and a phase transformation from the disordered L12 compound to the disordered fcc solid solution of Al in Ni was observed after milling for long periods. Partial amorphization occurs after prolonged periods of milling. The long-range-order parameter decreases monotonously with time in the early stages of milling and attains a zero value after relatively short periods of milling. The lattice parameter and the relative strain increase with milling time. Magnetic properties of ball-milled Ni3Al at 4.2 K differ markedly from those of the ordered state. Based on the magnetic data, it is concluded that short-range disordering could be the third source of energy storage during milling of Ni3Al. Exothermic heat effects resulting from atomic reordering and phase restoration and/or crystallization are evident in the DSC scans of ball-milled Ni3Al. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359974
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  • 3
    Digitale Medien
    Digitale Medien
    Vibrational dynamics of hydrogen-bonded HCl-diethyl ether complexes (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5127-5132 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We studied the relaxation of the H–Cl stretch vibration of hydrogen-bonded HCl-diethyl ether [HCl–(CH3CH2)2O] complexes at room temperature using femtosecond mid-infrared pump-probe spectroscopy. The lifetime of the H–Cl stretch vibration is determined to be 0.9±0.2 ps. The relaxation is found to occur via an intermediate state which causes a transient blue-shift of the H–Cl stretch frequency. This blue-shift indicates that the low-frequency (CH3CH2)2O⋅⋅⋅H–Cl hydrogen bond is the main accepting mode of the vibrational energy. The excited population of this hydrogen-bond mode decays with a time constant of 3.1±0.5 ps to the ground state. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.481069
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  • 4
    Digitale Medien
    Digitale Medien
    Nonequilibrium phase transformation and magnetic properties of Ni3Sn2 during mechanical milling (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1521-1527 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A nonequilibrium phase transformation in stoichiometric Ni3Sn2 during mechanical impact in a high-energy ball mill was monitored by the measurements of high-field magnetization, ac susceptibility, and x-ray diffraction. X-ray diffraction showed that the material transformed from the low-temperature Ni3Sn2 phase with Ni3Sn2-type orthorhombic structure to the high-temperature Ni3Sn2 phase with partially filled-up B8-type structure after 40 h of milling. Quenching was used to confirm the phase transformation during ball milling. The magnetization of the ball-milled high-temperature phase (metastable) is much higher than that of the quenched high-temperature phase, where both ball-milled and quenched high-temperature phases have higher magnetization than the low-temperature phase. The Curie temperature of our metastable high-temperature phase is quite close to that of the equilibrium phases (high- and low-temperature phases). The result is discussed in terms of atomic disordering induced by mechanical milling.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353226
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  • 5
    Digitale Medien
    Digitale Medien
    Atomic disorder induced by mechanical milling in the Nb3Au intermetallic compound (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5650-5653 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The behavior of the intermetallic A15 compound Nb3Au in the early stage of mechanical milling was studied. By following the degradation of the superconducting transition temperature and the increase of the lattice parameter as a function of milling time, it was found that Nb3Au exhibits atomic (chemical) disorder due to milling. A value for the ballistic jump frequency of the atoms was assessed. The behavior turns out to be very similar to that of Nb3Sn, although for long milling time Nb3Sn amorphizes, whereas Nb3Au transforms from the A15 structure to the bcc structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350498
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  • 6
    Digitale Medien
    Digitale Medien
    Influence of quenching speed on the superconducting transition temperature of YBa2Cu3O7−δ annealed in air at 650–1200 K (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1885-1887 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Both single and polycrystalline samples of YBa2Cu3O7−δ were annealed in air at different temperatures between 650 and 1200 K and subsequently quenched at two different speeds: the conventional quench in liquid nitrogen and a high-speed quench (5×104 K/s) using a special device. Both x-ray and ac-susceptibility measurements were used to investigate the influence of quenching speed on the oxygen ordering and Tc. During quenching partial reordering takes place. In the rapidly quenched samples more disorder was frozen in, which corresponds to a lower Tc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351174
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  • 7
    Digitale Medien
    Digitale Medien
    Transient absorption of vibrationally excited water (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 2592-2598 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We study the spectral response of the transition between the first and the second excited state of the O–H stretch vibration of HDO dissolved in liquid D2O with two-color femtosecond mid-infrared spectroscopy. The spectral response of this transition differs strongly from the fundamental absorption spectrum of the O–H stretch vibration. In addition, excitation of the O–H stretch vibration is observed to lead to a change of the hydrogen-bond dynamics of liquid water. We show that both these observations can be described with a refined quantum-mechanical version of the Lippincott–Schroeder model for hydrogen-bonded OH(centered ellipsis)O systems. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1432687
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  • 8
    Digitale Medien
    Digitale Medien
    Temperature dependence of vibrational relaxation in liquid H2O (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 1708-1713 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have determined the lifetime of the OH-stretch vibration in pure liquid water as a function of temperature using femtosecond mid-infrared pump–probe spectroscopy. The lifetime T1 increases from 260±18 fs at T=298 K to 320±18 fs at T=358 K. The increase in lifetime with temperature can be quantitatively explained from the decrease in overlap resonance between the OH-stretch vibration and the overtone of the H–O–H bending mode. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1485966
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  • 9
    Digitale Medien
    Digitale Medien
    Vibrational dynamics of the C–O stretch vibration in alcohols (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3182-3186 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present a study on the vibrational dynamics of the C–O stretch vibration of methanol and ethanol in carbon tetrachloride (CCl4) solution. The relaxation of the excited C–O stretch vibration was observed to occur in two steps. In the first step energy is transferred from the v=1 state of the C–O stretch vibration to an intermediate state with a time constant of 3.2±0.2 ps for methanol and 3.2±0.7 ps for ethanol. The intermediate state is most likely formed by the n=3 or 4 state of the C–O–H bending mode, which is also known as the torsional mode. In the second step energy is transferred from this intermediate state to low-energy modes, leading to a full equilibration of the energy. In methanol this thermalization occurs with a time constant of 28±1 ps. In ethanol the second step is faster, with a time constant of 12±2 ps. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1338974
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  • 10
    Digitale Medien
    Digitale Medien
    Femtosecond mid-infrared spectroscopy of aqueous solvation shells (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 8942-8948 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We use femtosecond two-color mid-infrared spectroscopy to study the dynamics of aqueous solutions of salts in HDO:D2O. We find that the lifetime of the O–H stretch vibration of HDO molecules in the solvation shell of the halogenic anions Cl−, Br−, and I− is much longer than the lifetime of the O–H stretch vibration of the HDO molecule in bulk D2O solution. This difference in lifetime allows for a clear separation of the response of the solvation shell from that of the bulk liquid. A detailed investigation of the spectral dynamics of the solvating HDO molecules reveals that the hydrogen-bond dynamics of these molecules are much slower than the hydrogen-bond dynamics of bulk liquid water. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1412249
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