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  • 1995-1999  (417)
  • 1990-1994  (360)
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  • 11
    Electronic Resource
    Electronic Resource
    Negative-ion mass spectrometric study of ion pair formation in the vacuum ultraviolet. I. N2O→O−+N+2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6556-6560 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Negative ion formation from N2O has been studied using synchrotron radiation in the 15–40 eV photon energy range. Only O− ion signal is observed by mass spectrometry. The onset of the photodissociation efficiency curve for O− from N2O is in good agreement with the thermochemical threshold of 15.79 eV for the formation of O−(2Pu)+N+2(X˜ 2∑+g). Several series of peaks are identified as resulting from predissociation from the Rydberg states converging to N2O+(A˜ 2∑+, B˜ 2∏, and C˜ 2∑+). In particular, two Rydberg series (ndσ and ndπ) converging to the C˜ state are observed most prominently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458291
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  • 12
    Electronic Resource
    Electronic Resource
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. VI. CH3X→X−+CH+3 (X=F, Cl, Br) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7500-7505 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ion-pair formation from photoexcited halomethanes, CH3X*→X−+CH+3 (X=F, Cl, Br) has been studied by measuring photodissociation efficiency curves of X− using synchrotron radiation in the 9.9–27.5 eV photon energy range. A new spectral feature is observed in each of the curves near the threshold for the removal of an na1 electron from CH3X (n=4, 6, and 8, respectively, for CH3F, CH3Cl, and CH3Br ). This feature, composed of two or three peaks in each case, is interpreted as resulting from photoexcitation to the Rydberg states converging to CH3X+(C˜ 2A1), which then predissociate into ion pairs through avoided potential energy surface crossings. The interpretation is based on the results of the inner-shell electron energy loss study by Brion and co-workers and the photoabsorption study by Hochmann and co-workers. Peak features are also observed in the X− efficiency curves near the ionization threshold for CH3X+(X˜ 2E). The origins of these peaks are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462401
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  • 13
    Electronic Resource
    Electronic Resource
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. IV. CH4→H−+CH+3 and CD4→D−+CD+3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6003-6006 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ion-pair formation from photoexcited methanes, CH@B|4 →H− +CH+3 and CD*4 →D− +CD+3, has been studied by measuring the efficiency curves of H− and D− using synchrotron radiation. Ion pairs are produced both by direct dissociation and predissociation of the npt2 (n=3–5) Rydberg state converging to the A˜ 2A1 state of CH+4/ CD+4. The 4pt2 and 5pt2 Rydberg states are observed here for the first time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460435
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  • 14
    Electronic Resource
    Electronic Resource
    Dissociative single, double, and triple photoionization of silicon tetrafluoride in the valence shell and silicon 2p regions (hν=33–133 eV) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4936-4948 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoionization of SiF4 in the valence shell and Si2p innershell regions has been studied using time-of-flight mass spectrometry and synchrotron radiation over the photon energy range 33–133 eV. Photoionization branching ratios are reported for stable singly and doubly charged ions arising from the various possible molecular and dissociative photoionization processes. The time-of-flight mass spectrometer used in the present work employs very efficient ion extraction fields and this results in very much higher relative abundances of energetic fragmentations than were reported in earlier published work [Lablanquie et al., J. Chem. Phys. 90, 7078 (1989)]. Photoion–photoion coincidence (PIPICO) techniques have been used to investigate the relative yields of Coulomb explosion decomposition products and threshold energies for dissociative double photoionization in the valence shell and silicon 2p regions. The dominant process in the Si2p region is (F++Si+). The PIPICO spectra show additional peaks with thresholds in the Si2p region and these structures arise from the dissociation of triply charged ions into the exit channels (F++SiF2+2), (F++SiF2+) and (F++Si2+). Of these the latter is the most probable process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460579
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  • 15
    Electronic Resource
    Electronic Resource
    Local density of states of aperiodic polymers using the localized orbitals from an ab initio elongation method (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8432-8440 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An elongation method, which was already proposed to calculate efficiently the electronic states of aperiodic polymers, is developed to provide the local density of states. Elongation method is carried out by repeating the uniform localization of wave functions with inclusion of the interaction between the cluster and an attacking molecule. At first, we develop this method to the ab initio level. Next, we show that the local density of states (LDOS) is obtained efficiently following the elongation step without treating the whole system directly. The validity of our method is examined via application to a hydrogen molecule cluster by comparing the results with those by the conventional ab initio method for the whole system. This approach makes it possible to investigate the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and their density of states on each site of a polymer chain, which will provide a novel approach to examine intra- and intermolecular reactivities within and between aperiodic polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463413
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  • 16
    Electronic Resource
    Electronic Resource
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. II. OCS→S−+CO+, O−+CS+, and CO2→O−+CO+ (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1710-1719 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ion-pair formation from photoexcitation of OCS and CO2 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 15–35 eV photon energy range. Negative ions S− and O− from OCS and O− from CO2 have been observed. The lowest onset energy in the photodissociation efficiency curve for each ion is in good agreement with the thermochemical threshold for the formation of the negative ion in the ground 2Pu state and its counterpart positive ion in the ground 2Σ+ state. There exist series of peaks with medium intensities in the efficiency curves of S− from OCS and O− from CO2; they are identified as resulting from predissociation of the Rydberg states converging to OCS+(B˜ 2Σ+) and CO+2(C˜ 2Σ+g), respectively. Broad peaks are observed at 18.4 eV (∼675 A(ring)) in the efficiency curves for both S− and O− produced from OCS. Predissociation of the excited valence state formed by the intravalence 9σ→10σ transition is considered to mainly contribute to these features. In addition, a broadband feature is present in the wavelength range of 400–620 A(ring) in the O− efficiency curve. The most likely candidate for the corresponding doorway state is the two-electron excited state involving simultaneous 9σ→10σ and 3π→4π transitions. In the case of the O− efficiency curve from CO2, two maxima observed at 21.4 (580 A(ring)) and 23.0 eV (538 A(ring)) are explained as resulting from the 3σu→5σg transition forming an excited valence state which effectively couples to the ion-pair continuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459098
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  • 17
    Electronic Resource
    Electronic Resource
    A theoretical synthesis of polymers by using uniform localization of molecular orbitals: Proposal of an elongation method (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5419-5431 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The elongation method, a new approach to calculating the electronic structure of polymers efficiently, is proposed as a model for real polymerization reactions following the normal chain reaction processes of initiation, propagation, and termination. The calculations are carried out by repeating the uniform localization of wave functions with inclusion of the interaction between the end group of the cluster and an attacking molecule. As a first step of this treatment, the validity of our method is examined via application to regular and irregular model polymers consisting of hydrogen molecules at the extended Hückel level and comparing the results with those obtained from the conventional variational method. Furthermore, this treatment is performed on the real polymers such as polyethylene and polypropylene stereoisomers, and is proved to be reliable with advantages in computational time and storage. The approach is promising for application to very large systems on which direct variational calculations of the whole system are impossible. Moreover, it should be emphasized that this approach can mimic real reaction coordinates, or can be considered a theoretical synthesis of polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461658
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  • 18
    Electronic Resource
    Electronic Resource
    Reactions of N(4S) atoms with NO and H2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8703-8708 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first-order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a direct abstraction of H atom from H2, and it gives calculated activation energy which is in good agreement with the present experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459257
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  • 19
    Electronic Resource
    Electronic Resource
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. III. SF6→F−+SF+5 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8717-8724 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ion-pair formation from photoexcitation of SF6 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 11.27–31.0 eV photon energy range. Negative ions F−, SF−6, and SF−5 have been observed. The appearance energy of the F− ion is about 1 eV higher than the thermochemical threshold for the formation of the pair of the ground state ions F−(1Sg) and SF+5(X˜1A1). The peak features observed in the F− efficiency curve are interpreted as resulting from transitions to neutral excited states with the 1T1u symmetry which effectively couple with ion-pair states through avoided potential surface crossings. The peaks assigned to diffuse Rydberg states are distinctively enhanced in the F− efficiency curve, probably because of large transition probabilities from the dissociative Rydberg states to the ion-pair states. In contrast, the excited states of valence type autoionize in a short period and have quite small branching to the ion-pair channel. Consequently, the corresponding peaks are markedly suppressed in the F− spectrum. Assignments of the peak features in the previous photoabsorption spectra are also performed by using the term values for related Rydberg and virtual valence orbitals. Other negative ions observed, SF−6 and SF−5, are produced by resonance capture of low energy electrons emitted by photoionization of the parent molecules, and are not of major concern of the present study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459259
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  • 20
    Electronic Resource
    Electronic Resource
    Stationary space analysis of the electronic structure of a polymer system: From cluster model to cluster-series model (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7086-7091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is pointed out that, in order to use cluster molecules as a model of a polymer system, only the electronic structure within the stationary space, which consists of molecular orbitals unaltered by the extension of a cluster, should be dealt with. As a first example of stationary space analysis, simple procedures to extract both extreme states of the polymer are presented, that is, the periodic extended states and the localized states or stationary canonical orbitals. This approach is essentially based on direct comparison among the electronic structures of a series of clusters not only in the extraction of stationary space but also in its analysis. So it should be called the cluster-series model rather than the usual cluster model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465060
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