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  • 1
    Electronic Resource
    Electronic Resource
    Electronic orbital alignment effects in the reaction Mg*(3p 1P1)+CH4→MgH+CH3 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6476-6480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the final state resolved far-wing action spectra for the MgCH4 reactive collision system. The results show a dramatic "Π-like'' orbital alignment preference in the reaction channel. The reactive channel action spectra for different MgH rotational states in v=0 are identical, suggesting that the reaction follows from a single approach geometry, with the product rotational distribution determined by exit channel effects. Based on these observations and molecular orbital considerations, we propose that the reaction proceeds in η2 approach geometry through a triangular C–Mg–H transition state. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469362
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetron sputtering of Fe onto GaAs substrates: Energetic bombardment effects (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4358-4365 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe films were deposited on (100) GaAs substrates by magnetron sputtering. Bombardment of the films during growth by energetic particles from the plasma had a significant impact on film properties including resistivity, crystallographic orientation, and stress. Preferred orientation of the (200) Fe planes parallel to the substrate surface was observed over a wide range of deposition conditions. The (200) Fe rocking curve widths of these films compare favorably with those of films deposited using molecular beam epitaxy, and the resistivities were comparable to that of bulk Fe. Positions directly in front of the cathode as well as low cathode power appear to favor the formation of (200) Fe texture, however, the rocking curve width and lattice parameter are relatively independent of substrate position and cathode power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352200
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  • 3
    Electronic Resource
    Electronic Resource
    Photofragmentation spectroscopy of Al+(C2H4) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11798-11805 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the structure and dissociation dynamics of the weakly bound bimolecular complex Al+(C2H4) by photodissociation spectroscopy in the 216–320 nm spectral region. Experimental studies are supported by ab initio electronic structure calculations of the ground and low-lying excited states of the complex. Al+ is the dominant photofragment observed throughout the absorption profile. C2H4+ charge transfer product is also observed for shorter photolysis wavelengths, λ〈252 nm. The Al+–C2H4 bond dissociation energy is measured as D0=0.37±0.15 eV. Three molecular absorption bands are observed and assigned to the transitions (2 1A1,1 1B1,1 1B2←1 1A1) in C2v equilibrium complex geometry. The excited states are of predominantly charge-transfer character correlating with the product channel Al(3s23p)+(C2H4)+. The 2 1A1 and 1 1B2←1 1A1 absorption bands appear broad and structureless. This observation is consistent with ab initio results that suggest a pathway for rapid nonadiabatic dissociation through a 1 1B2–1 1A1 surface crossing facilitated by a stretch in the C–C bond of ethylene. In contrast the 1 1B1←1 1A1 molecular band shows significant vibrational structure. Spectroscopic analysis yields a band origin (000=40 042 cm−1) and corresponding vibrational mode frequencies for the 1 1B1 excited state. The observed modes have been assigned to the intermolecular Al–C2H4 stretch of a1 symmetry (ν2=230 cm−1), the Al–C2H4 out-of-plane wag with b1-symmetry (ν3=328 cm−1), and two intramolecular ethylene modes of a1 symmetry at 1264 and 1521 cm−1. The assignment for these higher frequency ethylene modes is not conclusive. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479123
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  • 4
    Electronic Resource
    Electronic Resource
    Chemical dynamics of the reaction K*(5p 2P)+H2→KH(v=0;J)+H: Electronic orbital alignment effects (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6743-6748 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report results from scattering state spectroscopic studies of the excited state reaction K*(5p 2P)+H2→KH(v″,J″)+H. The final state resolved action spectra allow a direct measurement of essential features of the excited state potential surfaces, including regions of local maxima and minima. We observe a pronounced blue-wing–red-wing asymmetry in the reactive to nonreactive branching ratio, peaking in the neighborhood of a strong blue wing satellite. These results show that the dominant reaction pathway passes over a small activation barrier (350±100 cm−1) in Σ+-like orbital alignment. This result is consistent with an electron jump mechanism through a K+H−H ion-pair intermediate. In contrast, approach in Π-like alignment leads predominantly to nonreactive scattering. Our results suggest that a combination of steric and energetic effects determine the major quenching pathways for alkali metal atom-H2 systems. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478579
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  • 5
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy and dynamics of MgC2H4+ (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2285-2296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The weakly bound ion–molecule complex MgC2H4+ has been studied by photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer over the spectral range 218–510 nm. Mg+ is the major photofragment throughout this range, although for λ〈270 nm, charge-transfer dissociation to C2H4+ is observed as a minor channel. We have identified five absorption bands of MgC2H4+. The spectral assignment is facilitated by results from ab initio calculations for the ground and low-lying excited states of MgC2H4+. Three of the bands, 1 2B2←1 2A1, 1 2B1←1 2A1, and 2 2A1←1 2A1, are based primarily in the metal-centered Mg+(3p 2P←3s 2S) atomic transition. One of the remaining bands is assigned as 2 2B2←1 2A1, a transition correlating with the a 3B1u←X 1Ag forbidden band of C2H4, with mixed charge-transfer character. The final band, 3 2A1←1 2A1, is assigned to a metal-to-ligand charge-transfer transition, enhanced by coupling with the nearby 2 2A1 state. The 1 2B2←1 2A1 band is a broad continuum, indicative of fast predissociation in the upper state. A nonadiabatic dissociation mechanism involving C(Double Bond)C π-bond activation by Mg+(3p) is suggested by ab initio calculations. The 1 2B1←1 2A1 band shows pronounced vibrational structure with a strong progression in the Mg+–CH4 intermolecular stretch (ν2), and weaker progressions assigned to combination bands built on the intermolecular out-of-plane wag (ν3), and a CH2–CH2 wag (ν7). The observed vibrational constants are ω2=329, x22=−2.3, ω3=439, and ω7=1024 cm−1. Measurement of the photofragment kinetic energy release determines the bond dissociation energies for the ground state [D0″(Mg+–C2H4)=0.7±0.2 eV], and for the 1 2B1 excited state, [D0′(Mg+–C2H4)=1.8±0.2 eV]. Spectroscopic constants are in good agreement with ab initio predictions. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475613
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  • 6
    Electronic Resource
    Electronic Resource
    Scattering state spectroscopy of the reaction Mg*(3s3p 1P1)+CH4→MgH(v=0,1;N)+CH3 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5723-5727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report scattering state spectroscopic studies of the chemical quenching dynamics of Mg*(3p(1P)) by CH4. We have measured the final-state resolved action spectra for the MgH(v=1,N) reactive product channels, following excitation of the Mg*(3p)–CH4 transient bimolecular collision complex. As in earlier work on the ground vibrational state of the product, we have found a strong electronic orbital alignment effect: Reaction to the vibrationally excited product follows only on the attractive excited potential-energy surfaces in "Π-like" symmetry. For both MgH(v=0 and 1) product channels we have found that the rotational quantum state distribution is independent of laser excitation wavelength, indicating that the rotational energy partitioning is determined by exit channel dynamics. However, our results show that the product vibrational energy disposal is a function of excitation laser wavelength, suggesting that the vibrational energy partitioning is correlated with the collisional impact parameter. We have also carried out a careful search for the MgCH3 reactive product in this system, finding no evidence for any observable branching to this product. We discuss the implications of these results for the chemical dynamics of this metal-alkane reaction system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475981
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  • 7
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy of MgCH+4 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6452-6459 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation spectroscopy of MgCH+4 has been studied in a reflectron time-of-flight mass spectrometer. MgCH+4 molecular absorption bands are observed to the red of the Mg+(3 2PJ←3 2S1/2) atomic ion resonance lines. The photofragmentation action spectrum consists of a broad structureless continuum ranging from 310 nm to 342 nm, and peaking near 325 nm. In this spectral region, both the nonreactive (Mg+), and two reactive fragmentation products (MgH+ and MgCH+3) are observed, all with similar action spectra. The product branching is independent of wavelength, Mg+:MgCH+3:MgH+∼60:33:7. The absorption is assigned to the transition (1 2E←1 2A1) in C3v symmetry (with η3 coordination), followed by a geometrical relaxation of the complex toward states of 2B1 and 2B2 symmetry in C2v geometry (with η2 coordination). Dissociation requires a nonadiabatic transition to the ground electronic surface. Analysis of broadening in the photofragment flight time profile shows the nonreactive Mg+ product angular distribution to be isotropic, with an average translational energy release which increases slightly from Et∼370±150 cm−1 at 332.5 nm to Et∼520±180 cm−1 at 315 nm. These values are less than 2% of the available energy and are well below statistical expectations. Analogous experiments on MgCD+4 show the kinetic energy release in the nonreactive channel to be significantly larger for the CD4 case, ranging from Et∼540±180 cm−1 at 332.5 nm to Et∼830±200 cm−1. These results clearly demonstrate that the dissociation is nonstatistical. Preliminary ab initio potential surface calculations suggest a possible dynamical mechanism to explain these unusual results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471366
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  • 8
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy of MgO2+ (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8311-8318 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemically bound superoxide molecule MgO2+ has been studied by photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer over the spectral range 247–540 nm. The experimental observations are consistent with ab initio calculations showing the ground state of MgO2+ to be of Mg2+O2− superoxide character [Chem. Phys. Lett. 203, 215 (1993)]. Through the visible and near UV spectral range 280 nm〈λ〈540 nm, we observe weak continuum absorption with evidence for two overlapping bound–free absorption bands, assigned as 1 2B1←1 2A2 and 2 2B1←1 2A2 in C2v symmetry. These bands correspond to radiative charge-transfer transitions of the form Mg2+O2−→Mg+O2. Both Mg+ and MgO+ fragments are observed, with a clear threshold for branching to MgO+ at a photolysis wavelength of 330 nm. This threshold yields limiting values for the MgO2+ bond dissociation energies of D0″(MgO+–O)≤(3.75±0.04) eV and D0″(Mg+–O2)≤(1.13±0.11) eV. For photolysis wavelengths λ〈280 nm we observe a third structured absorption band showing a clear vibrational progression with an excited state vibrational mode spacing of ωe=520±15 cm−1. This electronic band is assigned as 3 2B1←1 2A2, with the upper state correlating to an excited electronic state of O2−. The vibrational progression is tentatively assigned to the ν2 (Mg–O) symmetric stretch mode of the complex (a1). © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477494
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  • 9
    Electronic Resource
    Electronic Resource
    Amorphous GeCu alloy for low temperature resistor fabrication (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3102-3104 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous germanium–copper alloy films (a-Ge1−xCux, 0.01≤x≤0.3) have been deposited and characterized at temperatures down to 3.9 K. The sheet resistivities of these films can be controlled by varying their copper content and are substantially higher than common thin film resistor materials. The films can be readily patterned by either wet etching or lift-off and are potentially useful for fabricating the high resistances necessary for observing the Coulomb blockade in single tunnel junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352997
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  • 10
    Electronic Resource
    Electronic Resource
    Collisional energy transfer in Na(4p–3d)–He,H2 collisions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1101-1104 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the direct collisional energy transfer process Na*(4p)+M→Na*(3d)+M, where M=He,H2 under gas cell conditions. We have measured the temporal profiles of the Na(3d–3p) sensitized fluorescence as a function of quenching gas pressure and fit the profiles to a two-state rate equation model to obtain the quenching rate coefficients from the Na*(4p) state. The total energy transfer rate coefficient out of the 4p state for He is small [(0.5±0.2)×10−10 cm3/s]. The total quenching rate coefficient out of the 4p state is much larger for H2[(3.9±0.5)×10−10 cm3/s]. Evidence suggests that the energy transfer rate coefficient for the 4p–3d process is ∼2.0×10−10 cm3/s with the remainder of the 4p quenching being predominantly reactive. We also compare the far-red wing absorption line shapes for the NaHe and NaH2 systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464333
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