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  • 11
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 134-139 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the resonant two-photon ionization (R2PI) spectra of three van der Waals (vdW) complexes p, m, o-C6H4F2(centered ellipsis)NH3(ND3) through the S1←S0 transition with mass selectivity. The stretching frequencies of the three vdW complexes were found to be quite close (86 cm−1). From the photodissociation mechanism and the relationship between anharmonicity of the stretching vibration and the dissociation energy, we estimated the dissociation energies of all the three vdW complexes in the S0 and S1 states. A quantum ab initio calculation on p-C6H4F2(centered ellipsis)NH3 at the MP2/6-31G** level gave the following geometry: The N atom of NH3 is located on the symmetry axis (Z-axis) and 3.53 Å above the benzene ring; the C3 axis of NH3 is at an angle of 52.5° with the Z-axis of p-C6H4F2 with one of the hydrogen atoms pointing towards the benzene ring; the rotation of NH3 around the Z-axis is nearly free. The calculated bond dissociation energies and the expectation of internal rotation are consistent with our experimental results. © 1999 American Institute of Physics.
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4911-4918 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have carried out a comprehensive study on the photoionization/fragmentation of Cr(CO)6 by using the time-of-flight mass spectrometry (TOFMS) technique and a synchrotron radiation source in the photon energy range of ∼8–40 eV. The appearance potentials (AP) of all the observed fragment ions were accurately determined, and those of some fragments, e.g., the doubly charged ions and the carbide fragments, were determined for the first time. The corresponding thermodynamic properties of these fragment ions have been derived. © 1997 American Institute of Physics.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8920-8928 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The weakly bound Al(centered ellipsis)H2 complex was prepared in a pulsed supersonic beam and studied with laser fluorescence excitation spectroscopy. Transitions to bound bend–stretch levels in the electronic state correlating with the Al(5s)+H2 asymptote have been observed. Resonance fluorescence from the excited levels could be detected only very weakly. These excited levels decay mainly nonradiatively, and the excitation spectrum was obtained by monitoring emission from the lower Al atomic levels, 4s and 3d, and AlH A→X chemiluminescence due to AlH(A 1Π) formed in the reactive decay of the excited Al(5s)(centered ellipsis)H2 complex. The action spectra show a progression of bands which were assigned as a progression in the excited state Al–H2 stretch vibrational mode. The AlH chemiluminescence was recorded with 0.8 nm spectral resolution. Emission in the A–X (0,0) and (1,1) bands, from the v′=0 and 1 vibrational levels of the A 1Π state, was observed. The relative emission intensity of the Q branches was found to be depressed from that expected if the e and f levels of the excited state were equally populated. The experimental spectra were compared with simulations in order to estimate the rovibrational Λ-doublet state distribution in the A 1Π state. A strong propensity to form e levels, with considerable rotational excitation, was found. The Λ-doublet propensity is believed to be a consequence of the A′ symmetry of the Al(5s)+H2 potential energy surface on which the reagents initially approach one another. © 1998 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3522-3530 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser fluorescence excitation spectrum of the AlNe complex, in the vicinity of the Al atomic 3d←3p and 5s←3p atomic transitions, is reported. Transitions out of the v=0 vibrational levels of both lower-state spin-orbit levels, X1 2Π1/2 and X2 2Π3/2, to vibrational levels of the C 2Δ, D 2Π, and H 2Σ+ AlNe electronic states were observed. From observations of the onset of excitation to the Al(3d)+Ne dissociation continuum, dissociation energies for the various AlNe electronic states were determined. Ab initio calculations of AlNe electronic states correlating with the ground Al(3p)+Ne atomic asymptote were also carried out. The X1 2Π1/2 and X2 2Π3/2 binding energies computed using the calculated AlNe(X 2Π, A 2Σ+) potential energy curves were in reasonable agreement with the experimental determinations. The experimentally determined dissociation energy for the X2 2Π3/2 level is significantly larger than that of the ground X1 2Π1/2 level (D0=32.3±0.3 and 14.1±0.3 cm−1, respectively). © 1998 American Institute of Physics.
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10236-10246 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of a series of complexes Mg+–C6H5X (X=H, F, Cl, Br) has been studied. The formation of Mg+ was found to be the predominant dissociation pathway. We monitored the photodissociation product as a function of the excitation wavelength in a broad spectral region. Experiments on the complexes with different halide substitutions showed similar action spectra. This is explained by a similar structure shared by these complexes with Mg+ being above the benzene ring. In the photodissociation of Mg+–(C6H5F), MgF+ is also formed besides Mg+. The action spectra corresponding to these two channels were found to be different, and the MgF+ channel is believed to be from a different isomer. The experimental results are consistent with our quantum ab initio calculations. © 2000 American Institute of Physics.
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  • 16
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7837-7843 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Selenium cluster cations are produced by the combination of laser vaporization and supersonic expansion techniques. Each small cluster cation Sen+ (n=3–8) is mass selected separately and subjected to one-photon laser photodissociation processes. The parent and daughter cluster ions are detected using a reflectron time-of-flight mass spectrometer. The appearance potentials of all the observed cluster fragment ions are estimated from their yield curves as a function of the laser wavelength. The neutral dimer evaporation is found to be the lowest energy photodissociation channel. In general, the odd-numbered cluster cations have much larger dissociation thresholds than those of the even-numbered cluster cations. In addition, the dissociation thresholds of the odd-numbered cations decrease with the increasing cluster size, while those of the even-numbered clusters increase with the increasing cluster size. A sequential neutral dimer evaporation mechanism is demonstrated in the photodissociation of some cluster cations at high photon energies. © 1999 American Institute of Physics.
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 220-228 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new molecular electronic band system has been observed by laser fluorescence excitation in a free-jet supersonic expansion of photolyzed trimethylaluminum diluted in seed gases containing molecular nitrogen. The overwhelming majority of observed bands displayed the rotational structure of a 1Π←1Σ transition. The change in the rotational constant B″ of a band at 36 389 cm−1, assigned as the origin band, upon 15N substitution was consistent with the assignment of the molecular carrier as AlNC, and the value of B″ for the Al14NC(X˜ 1Σ+) isotopomer agreed with that previously determined by pure rotational spectroscopy. To carry out a vibrational assignment, resolved emission spectra were recorded for excitation of the ten strongest bands. With one exception, all these bands were found to involve excitation out of the ground vibronic level. Vibrational quantum numbers for the upper levels were assigned for most bands, and the upper state appears to be linear, with 1Π symmetry. A band at 28 754 cm−1, assigned to AlNC by Fukushima [Chem. Phys. Lett. 283, 337 (1998)], was also investigated. The lower-state vibrational spacings in its resolved emission spectrum were different than for the bands discussed above. Based on the rotational constants determined in a rotational analysis of this band, the molecular carrier of this transition is assigned as the isomer AlCN. © 1999 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9474-9482 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absolute photoabsorption cross sections σa and photoionization quantum yields η of Cr(CO)6, Mo(CO)6, and W(CO)6 are measured in the wavelength range of ∼300–1600 Å. We have also estimated the photoionization cross sections σi and the neutral photodissociation cross sections σd from σa and η. Main absorption features are tentatively assigned with the help of the MO diagram and the photoelectron spectroscopic data of M(CO)6(M=Cr,Mo,W). Large optical oscillator strength distributions and neutral photodissociation cross sections are obtained at the photon energies far beyond the first ionization potential. Our studies revealed the valence excitation nature of the superexcited states in the extreme ultraviolet region. It is suggested that the neutral photodissociation in this region shares a similarity with that in the UV region below the first ionization potential because they both involve a repulsive ejection of the first CO ligand. © 1997 American Institute of Physics.
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2368-2376 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new density functional theory is developed for inhomogeneous mixtures of polymeric fluids by combining Rosenfeld's fundamental-measure theory for excluded volume effects with Wertheim's first-order thermodynamic perturbation theory for chain connectivity. With no adjustable parameters, theoretical predictions are in excellent agreement with Monte Carlo simulation data for the density distributions and for the adsorption isotherms of hard-sphere chains near hard walls or in slit-like pores. This theory is applied to calculate the force between two parallel hard walls separated by hard-sphere chains at different densities. Calculated results indicate that the chain-mediated force is attractive and decays monotonically with separation at low chain densities, it oscillates at high chain densities and in between, it is attractive at small separation and repulsive at large separation. This new density functional theory is simpler than similar theories in the literature and is directly applicable to mixtures. © 2002 American Institute of Physics.
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  • 20
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 561-570 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigated free and water-solvated gas phase nitrate anions, NO3−(H2O)n (n=0–6), by photodetachment photoelectron spectroscopy and theoretical calculations. We obtained the electronic structure and electron binding energies of the free and solvated NO3− at three detachment photon energies, 4.661, 6.424, and 7.866 eV. The ground and two low-lying electronic excited states of the NO3 radical (X 2A2′,A 2E″,B 2E′) were observed at the 6.424 and 7.866 eV photon energies. The photoelectron spectra of the solvated nitrate complexes are similar to that of the bare NO3−, except that they become broadened and diffuse due to the solvation. The spectrum of NO3−(H3O)3 showed a resolved vibrational progression of the N–O symmetric stretching (1000 cm−1), suggesting the cluster possesses a high symmetry. NO3− and NO3 were calculated at various levels of theory. Based on the good agreement between density functional theory calculations and experiment for NO3− and NO3, we carried out systematic calculations for NO3−(H2O)n (n=1–6) using primarily density function theory methods. The calculations indicate that NO3−(H2O)n (n=1–3) are all planar, with the first three H2O forming the first solvation shell around NO3−, giving rise to a highly symmetric C3h NO3−(H2O)3. The next three waters form a second solvation shell without direct contact with NO3−. The C3h NO3−(H2O)3 solvation structure was observed to be rather robust and largely preserved in the larger clusters. © 2002 American Institute of Physics.
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