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  • 1
    Electronic Resource
    Electronic Resource
    The spontaneous resonance Raman scattering of CH3I in a supersonic jet (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2806-2817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The resonance Raman scattering of methyl iodide cooled in neat and seeded supersonic jets has been observed. The incident radiation is resonant with the X→B Rydberg transition (∼200 nm). To our knowledge this is the first reported observation of the resonance Raman scattering of jet-cooled species. Depolarization ratio measurements determine the rotational temperature of the molecular beam to be 10 K (4% CH3I/2 atm He). The only observed spectral evidence of (CH3I)n species (n≥2) in the cooled molecular beam is the appearance of the resonance Raman spectra of I2 produced by the photodecomposition of methyl iodide clusters. The nascent I2 is born with an extremely hot (∼1000 K) vibrational distribution. The excitation profile of the I2 vibrational resonance Raman scattering reveals that the absorption band of the clusters are much broader than that of the monomer. Semiempirical calculations (AM1) predict a CH3I dimer with a bent "heat-to-head'' ground-state equilibrium structure which is a favorable orientation for the production of I2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457927
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  • 2
    Electronic Resource
    Electronic Resource
    Depolarization ratios of resonance Raman scattering in the gas phase (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4125-4143 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: All three scattering invariants, isotropic, antisymmetric, and anisotropic, contribute to the resonance Raman (RR) activity of randomly oriented gas phase scatterers as shown in a sum-over-all-rovibronic-states approach regardless of the symmetry of the vibrational transition. Thus, in the gas phase, totally symmetric modes may have Raman depolarization ratios (ρ)〉3/4 and nontotally symmetric modes may have ρ≠3/4 for resonance excitation frequencies. Large ρ dispersion effects are predicted when the RR scattering cross section is dominated by the contribution of a single vibronic band. The extent of this purely rotational effect sensitively depends on the excitation frequency and the resonant dephasing rate. These depolarization ratio effects are demonstrated by the resonance Raman scattering of CH3I (B state) and NH3, ND3 (A state) for both a and e vibrational bands as well as for J (NH3) and K (CH3I) resolved rovibrational features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455771
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  • 3
    Electronic Resource
    Electronic Resource
    Rovibrational Raman scattering of CH3I vapor: Resonance with a perpendicularly polarized electronic transition (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4115-4124 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman scattering due to resonance with a perpendicularly polarized electronic transition of a symmetric top molecule in the gas phase is described in a sum-over-all-states approach. The derived intensity and depolarization ratio expressions in an irreducible two-photon tensor basis are applied to the analysis of the ν2 (a1 ) and ν6 (e) bands of CH3 I derived from resonance with the predissociated X→B absorption system. A lifetime of 0.5±0.1 ps is determined for the electronic origin and several K-specific rovibronic levels of the v'6 =1 band of the resonant excited state. These results are contrasted with recent dynamical interpretations of the corresponding jet-cooled CH3 I absorption spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455770
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  • 4
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet laser/time-of-flight mass spectroscopy: Ion-pair spectra of 79Br35Cl (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8666-8672 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A newly built vacuum ultraviolet (VUV) laser/time-of-flight mass spectrometer is described, which has been used to record the first vibrationally and rotationally resolved spectra of the E0+ ion-pair state ←X0+ ground state transition of jet-cooled bromine monochloride BrCl, near 145 nm. The mass resolution of the instrument (m/Δm≈1000) was sufficient to obtain single isotopomer data. Preliminary results for 79Br35Cl are reported. Like other interhalogens, BrCl vibronic band intensities vary widely in the VUV, presumably as a result of excited state perturbations. This scenario has been corroborated by the observation of an irregularly spaced vibrational progression, and the irregular behavior of the excited state rotational constants as a function of v'.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466721
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  • 5
    Electronic Resource
    Electronic Resource
    Mass-resolved two-photon spectra of Kr2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5881-5889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: (2+1) resonantly enhanced multiphoton ionization spectra of jet-cooled Kr2 between ≈91 800 and 94 100 cm−1 have been recorded. Single isotopomer excitation spectra were obtained using time-of-flight mass detection. Vibronic structure for several Rydberg ← ground state transitions involving excited gerade states which dissociate to Kr+Kr* (4p55p) have been unambiguously analyzed for the first time, and molecular constants derived. Bond lengths were estimated from Franck–Condon calculations. These results compare favorably with recent ab initio calculations. Excited state predissociation effects were inferred from excitation spectra obtained by monitoring atomic daughter fragment ions in TOF. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469322
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  • 6
    Electronic Resource
    Electronic Resource
    Mode-specific subpicosecond photodissociation dynamics of the methyl iodide B state (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 288-296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibronically specific, subrotational period lifetimes of the predissociated B state (201–190 nm) of CH3I and CD3I are determined by spontaneous resonance Raman scattering measurements of depolarization ratios and rotationally resolved Raman excitation profiles (REPs). The lifetime of the electronic origin, methyl rocking (ν6), and methyl umbrella (ν2) band are the same in CH3I (0.5 ps) and CD3I (1.2 ps). However, the predissociation rate decreases by a factor of ∼3 when one quantum of ν3, the methyl–iodine stretch, is excited on the B-state surface. The only vibrational mode which is found to accelerate the B-state predissociation rate is the a1 C–H (C–D) stretch. The lifetime of the ν1 vibronic level decreases by nearly an order of magnitude for CH3I (60 fs) and by a factor of 2 for CD3I (0.6 ps) relative to the corresponding electronic origin level. In addition, K-resolved REP analysis reveals predissociation rates to be K independent. These mode-specific predissociation rates are ascribed to the shape of the multidimensional reaction coordinate in the region of the curve crossing between the bound (B state) and unbound surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461485
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  • 7
    Electronic Resource
    Electronic Resource
    Two-dimensional hole gas in Si/Si0.85Ge0.15/Si modulation-doped double heterostructures (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2701-2703 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si/Si0.85Ge0.15/Si p-type modulation-doped double heterostructures have been grown by the ultrahigh vacuum/chemical vapor deposition technique, and mobility enhancement has been observed at low temperatures. For heterostructures with Si layers doped with boron to ∼1×1019 cm−3, hole mobilities of ∼900 cm2/V s at 14 K have been obtained. No carrier freeze-out behavior has been observed at low temperatures. The existence of two-dimensional hole gas was determined by the tilted-field Shubnikov–de Haas measurement. Both Si/SiGe and SiGe/Si heterointerfaces were found to be equivalent and of excellent interfacial quality. The valence-band maximum of Si0.85Ge0.15 alloy has been estimated to be (approximately-equal-to)0.95 meV higher than that of Si. A hole effective mass of 0.44±0.03m0, which is consistent with the interpolation of the bulk band structures for the Si0.85Ge0.15 alloy, has been obtained for the heterostructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101019
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  • 8
    Electronic Resource
    Electronic Resource
    High hole mobility in Si/Si1−xGex/Si p-type modulation-doped double heterostructures (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2333-2335 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality Si/Si1−xGex/Si p-type modulation-doped double heterostructures with x=0.12 and 0.15 have been grown by the ultrahigh vacuum/chemical vapor deposition technique. Hole mobilities as high as ∼3700 cm2/V s at 14 K have been obtained for heterostructures with x=0.12, at a sheet carrier concentration of ∼8×1011 cm−2. This is the highest hole mobility ever reported for p-type Si material at these carrier concentrations. The electrical properties of these heterostructures at low temperatures are those expected of a two-dimensional hole gas at Si/SiGe and SiGe/Si heterointerfaces. The high hole mobility is indicative of excellent interfacial properties. Peak mobilities were observed to depend on the level and proximity of remote B dopant species, as well as the Ge content of the alloyed layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102274
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  • 9
    Electronic Resource
    Electronic Resource
    Resonant exciton effects in InAs monolayer insertions in a GaAs matrix (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7164-7168 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report resonant luminescence studies in ultrathin InAs quantum-well structures. Under double resonant conditions, sharp lines induced by longitudinal optical phonons were observed in the emission spectrum, in addition to the broad band luminescence. These sharp lines exhibited moderate circular polarizations whereas the linear polarization was negligible, indicating a resonant luminescence process. The properties of these sharp lines observed in InAs monolayer quantum wells are quite different from those observed previously in GaAs-AlxGa1−xAs quantum wells under similar conditions. InAs phonons were found to participate in the exciton resonant scattering process at high magnetic fields where double resonant conditions are fulfilled. InAs-like phonon energy is determined to be close to 29.9 meV, in good agreement with the energy expected for a uniform ultrathin elastically strained InAs layer. We performed various circular and linear polarizations to investigate the resonant luminescence process in thin InAs layers inserted in GaAs. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361428
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  • 10
    Electronic Resource
    Electronic Resource
    Artifacts in magnetic resonance imaging from metals : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4712-4714 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Metallic biomedical implants, such as aneurysm clips, endoprostheses, and internal orthopedic devices give rise to artifacts in the magnetic resonance image (MRI) of patients. Such artifacts impair the information contained in the image in precisely the region of most interest, namely near the metallic device. Ferromagnetic materials are contraindicated because of the hazards associated with their movement during the MRI procedure. In less-magnetic metals, it has been suggested that the extent of the artifact is related to the magnetic susceptibility of the metal, but no systematic data appear to be available. When the susceptibility is sufficiently small, an additional artifact due to electrical conductivity is observed. We present an initial systematic study of MRI artifacts produced by two low susceptibility metals, titanium (relative permeability μr≈1.0002) and copper (μr≈0.99998), including experimental, theoretical, and computer simulation results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361649
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