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  • American Institute of Physics (AIP)  (39)
  • American Chemical Society (ACS)
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4035-4041 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute cross sections for electron-impact ionization of the SiF3 free radical from threshold to 200 eV are presented for formation of the parent SiF+3 ion and the fragment SiF+2, SiF+, and Si+ ions. A 3 keV beam of SiF3 is prepared by near-resonant charge transfer of SiF+3 with 1,3,5-trimethylbenzene. The beam contains only ground electronic state neutral radicals, but with as much as 1.5 eV of vibrational energy. The absolute cross section for formation of the parent ion at 70 eV is 0.67±0.09 A(ring)2. At 70 eV the formation of SiF+2 is the major process, having a cross section 2.51±0.02 times larger than that of the parent ion, while the SiF+ fragment has a cross section 1.47±0.08 times larger than the parent. Threshold measurements show that ion pair dissociation processes make a significant contribution to the formation of positively charged fragment ions.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4042-4047 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute cross sections are measured for electron impact ionization and dissociative ionization of SiF2 from threshold to 200 eV. A fast (3 keV) neutral beam of SiF2 is formed by charge transfer neutralization of SiF+2 with Xe; it is primarily in the ground electronic state with about 10% in the metastable first excited electronic state (a˜ 3B1). The absolute cross section for ionization of the ground state by 70 eV electrons to the parent SiF+2 is 1.38±0.18 A(ring)2. Formation of SiF+ is the major process with a cross section at 70 eV of 2.32±0.30 A(ring)2. The cross section at 70 eV for formation of the Si fragment ion is 0.48±0.08 A(ring)2. Ion pair production contributes a significant fraction of the positively charged fragment ions.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 68-73 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Previous reports of threshold resonances occurring in the photodetachment spectra of molecular anions have provided detailed information about the nature of dipole-supported states and the dynamics of autodetachment from the vibrationless level. In this paper we report the first observation and analysis of rotational band structure in an excited vibrational level of a dipole-supported state. The 1 cm−1 resolution laser photodetachment spectrum of cyanomethyl anion (CH2CN−), the conjugate base of acetonitrile, was recorded in the 12 500–13 700 cm−1 region using ion cyclotron resonance spectrometry. Rotational assignment of the resonances occurring in this region provides evidence for vibrational-to-electronic coupling in the autodetachment process.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 823-829 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute cross sections for electron-impact ionization of the SiF free radical from threshold to 200 eV are presented for formation of the parent SiF+ ion and the fragment Si+ and F+ ions. A fast beam of SiF is prepared by charge transfer neutralization of an SiF+ beam. The radicals form in the ground electronic state and predominantly in their ground vibrational state, as shown by agreement of the measured ionization threshold with the ionization potential. The absolute cross section for SiF→SiF+ at 70 eV is 3.90±0.32 A(ring)2. The ratio of cross sections for formation of Si+ to that for SiF+ at 70 eV is 0.528±0.024; the ratio for formation of F+ to that of SiF+ is 0.060±0.008. The observed threshold energy for Si+ formation indicates the importance of ion pair formation SiF→Si++F−. Breaks in the cross section at 14.3 and 17 eV are assigned as dissociative ionization thresholds.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1460-1463 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and operational characteristics of a capacitance bridge detector and accompanying signal lock system are presented. The signal lock is especially well suited for the measurement of small changes in ion concentration during photochemical experiments, thereby alleviating problems caused by resonant frequency shifts.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2257-2261 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and construction of a nanoelectrospray ion source for a triple quadrupole mass spectrometer that is used for identification and analysis of minimum peptide amounts is described. This interface exhibits several improvements over commercially available devices: a new capillary holder that allows very simple loading and placement of the spray capillary, and a rotary stage that enables reproducible adjustment of the capillary's angle at the orifice of the mass spectrometer. We also introduced a pressure-regulating system for fast and reproducible adjustment of the static backing air pressure onto the sample solution in the spray capillary. Furthermore, an electric safety circuit increases handling and operation safety of the nanoelectrospray interface. © 1999 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5284-5289 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the 1 cm−1 resolution electron photodetachment spectra of cyanomethyl anion and its deuterated analog, trapped and detected in an ion cyclotron resonance spectrometer. Many sharp resonances were observed in the threshold region corresponding to rovibrational transitions from the ground electronic state to a dipole-supported state of the anion which subsequently undergo electron autodetachment. An assignment of the rotational transitions has been carried out, yielding rotational constants. Using spectral band intensities, we have estimated the electron binding energy of the dipole-supported state as 0.020 (±0.006) eV. The adiabatic electron affinities of the neutral radicals ⋅CH2CN and ⋅CD2CN are found to be 1.560±0.006 and 1.549±0.006 eV, respectively. Features of the dipole-supported state in this system have been compared to those in acetaldehyde enolate.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 572-580 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We predict stable geometrical structures and interaction energies of Ni clusters using non self-consistent electron density functional based corrected effective medium (CEM) and MD/MC-CEM methods. A plot of the reaction energies for the atomic ejection process, NiN+1→NiN+Ni, for Ni24–Ni55 displays a number of informative characteristics: (a) peaks and valleys represent internal structural rearrangement in which the number of core atoms increases by at least one and; (b) a plateau at N=50–54 is associated with the closing of the second MacKay icosahedron at Ni55. The lowest energy structures of NiN clusters for N=24–55 are dissimilar generally to those of both rare gas clusters and fragments of the bulk crystal lattice except where a stable icosahedral or bulk core is present. The growth scheme for N〈50 is determined by the stability and structure of the changing number of core atoms. By contrast, the growth scheme for 51≤N≤55 is determined by the addition of surface atoms to a very stable and invariant 13-atom icosahedral core. The theoretical predictions are compared to available model growth schemes and experimental data. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1994-1996 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical band gap in 40 nm Ga1−xInxN/GaN single heterostructures is investigated in the composition range 0〈x〈0.2 by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parameters b are derived for pseudomorphically stressed GaInN on GaN: b=2.6 eV (PR) and b=3.2 eV (PL in localized states). Using experimental deformation potentials of GaN, b=3.8 eV is extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1691-1693 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face. © 1998 American Institute of Physics.
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