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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6959-6962 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An experimental technique capable of directly determining the intrinsic reorganization energies of bimolecular electron transfer reactions is described. Appropriate solution phase redox species are prepared in the gas phase using electrospray ionization and probed using photodetachment spectroscopy. Five metal complex anions involved in the Fe2+–Fe3+ redox couple are investigated and the intramolecular reorganization energies are measured directly from spectral features due to removing the most loosely bound 3d electron from the Fe(II)-complexes. The photodetachment spectra also yield electronic structure information about the Fe2+–Fe3+ redox couple and provide a common electronic structure origin for the reducing capability of the Fe(II)-complexes, the most common redox reagents. © 2000 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 7388-7395 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structures of CuX2 (X=Cl and Br) have been investigated in the gas phase by means of anion photodetachment photoelectron spectroscopy and ab initio theory. The photoelectron spectra of CuX2− were recorded at two photon energies, 193 and 157 nm. Well-resolved and rich photodetachment features in the spectra provide unprecedented details for the low-lying electronic states of CuCl2 and CuBr2. The excitation energies for five low-lying electronic states of CuX2 were determined, and they explain well the two previously observed optical absorption bands. The electron affinities for CuCl2 and CuBr2 were determined to be identical, 4.35±0.05 eV within the experimental uncertainty. Both the anions and neutral CuX2 species were calculated to be linear with only a slight bond length variation between the charged and neutral species. The calculated electron affinities and vertical excitation energies for the excited states agree well with the experimental values, yielding a definite assignment for the electronic states of CuCl2 and CuBr2. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10837-10840 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Despite its ubiquity in nature, SO42− as an isolated dianion has never been detected because of its electronic instability as a result of the two negative charges. This study shows how the first few waters solvate and stabilize an isolated SO42−, molecule-by-molecule, using photodetachment spectroscopy and theoretical calculations. We find that the minimum number of water required to stabilize a free SO42− is three. The first four waters bind tightly to SO42−, each forming two H-bonds with SO42− without inter-water H-bonding. The charges of the dianion are stabilized sufficiently that additional waters form only single H-bonds with SO42− and that inter-water H-bonding is observed starting at n=5. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10928-10933 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of ClOx (x=2–4) radicals were experimentally investigated using anion photoelectron spectroscopy of the respective anions at several photon energies. The electron affinities of ClO3 and ClO4 were obtained for the first time and were found to be very high, 4.25±0.10 and 5.25±0.10 eV, respectively. Three low-lying excited states were observed for ClO2 with excitation energies of 2.10 eV (2B2), ∼2.60 eV (2A1 and 2A2). The 2A1 and 2A2 states were found to be nearly degenerate. Two low-lying states were observed for ClO3 at ∼1.20 eV (2A2) and ∼2.65 eV (2E), whereas no excited state was observed for ClO4 even at our highest photon energy of 157 nm (7.866 eV). The photoelectron spectra were assigned and compared with available theoretical calculations. The excellent agreement between the experimental and theoretical results confirmed the previous calculations. © 2000 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 653-661 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoelectron spectra of the three isomers of the benzene dicarboxylate dianion (o-, m-, and p-BDC2−) were measured in the gas phase at five photon energies. Detachment features from the carboxylate groups and the π electrons of the ring were clearly observed and distinguished. The electron binding energies were found to increase from the very small value of ∼0.2 eV in o-BDC2− to about 1.0 eV in p-BDC2−, due to the reduced Coulomb repulsion as the two excess charges become farther apart. We found that the repulsive Coulomb barrier (RCB) for detaching electrons from the carboxylates decreases from o-BDC2− to p-BDC2−. However, the RCB for detaching the ring π electrons was found to be significantly higher and remain constant for the three isomers. This distinct anisotropy in the RCB involving different detachment channels is related to the different intramolecular Coulomb repulsions experienced by electrons localized on the carboxylates and the ring. Theoretical calculations were performed to obtain the equilibrium structures of both the dianions and the monoanions and to gain insight into the intramolecular electrostatic interactions. The two carboxylates in m- and p-BDC2− were shown to be in-plane with the ring whereas the strong Coulomb repulsion in o-BDC2− forces the carboxylate groups out of the plane of the ring. The theoretical results clearly show the localized nature of the excess charges on the carboxylates and help us understand the intramolecular Coulomb repulsions within the three dianions. © 2000 American Institute of Physics.
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2889-2892 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a photoelectron spectroscopic study of F−(H2O)n (n=1–4) at 193 and 157 nm. In addition to a detachment feature from F−, we observed a higher binding energy feature in all spectra due to ionization of the solvent molecules leading to F−(H2O)n+ charge-transfer states. Detachment of an electron from F− in F−(H2O) reaches the transition state region of the reaction, F+H2O→HF+OH. The bound to non-bound transition resulted in a long tail at the low binding energy side in the photoelectron spectrum of F−(H2O). We estimated that the neutral F(centered ellipsis)H2O complex at the anion geometry, which is near the transition state region of the H-abstraction reaction, is 6±1 kcal/mol above the F+H2O asymptote, consistent with a previous estimation of a 4 kcal/mol entrance barrier height for this reaction. © 2001 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1957-1966 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A magnetic-bottle time-of-flight (TOF) photoelectron spectrometer, coupled with an electrospray ionization source, has been developed for the investigation of multiply charged anions in the gas phase. Anions formed in the electrospray source are guided by a radio-frequency quadrupole ion guide into a quadrupole ion trap, where the ions are accumulated. A unique feature of this apparatus involves the coupling of a TOF mass spectrometer to the ion trap with perpendicular ion extraction. The ion trap significantly improves the duty cycle of the experiments and allows photodetachment experiments to be performed with low repetition-rate lasers (10–20 Hz). This novel combination makes the photodetachment photoelectron spectroscopy studies of multiply charged anions possible for the first time. Furthermore, the perpendicular extraction of ions, pulsed out of the ion trap, to the TOF mass spectrometer allows the ion energies to be conveniently referenced to ground, simplifying the configuration of the TOF mass spectrometer and the subsequent magnetic-bottle TOF photoelectron spectrometer. The mass resolution (M/ΔM) achieved is about 800 for smaller ions. The magnetic-bottle photoelectron spectrometer resolution is about 11 meV full width at half maximum for 0.5 eV photoelectrons with an overall resolution of ΔE/E∼2%. The detailed design, construction, and operation of the new apparatus are presented. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4497-4509 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the first observation and photodetachment photoelectron spectroscopic study of a series of hexahalogenometallates dianions MCl62− (M=Re, Os, Ir, and Pt) and MBr62− (M=Re, Ir, and Pt) in the gas phase. All of these species were found to be stable as free gaseous doubly charged anions. Photoelectron spectra of all the dianions were obtained at several detachment photon energies. The photon-energy-dependent spectra clearly revealed the dianion nature of these species and allowed the repulsive Coulomb barriers to be estimated. The binding energies of the second excess electron in MCl62− (M=Re, Os, Ir, Pt) were determined to be 0.46 (5), 0.46 (5), 0.82 (5), and 1.58 (5) eV, respectively, and those in MBr62− (M=Re, Ir, Pt) to be 0.76 (6), 0.96 (6), and 1.52 (6) eV, respectively. A wealth of electronic structure information about these metal complexes were obtained and low-lying and highly-excited electronic states of the corresponding singly charged anions were observed. Detachment from metal d orbitals or ligand orbitals were observed and could be clearly distinguished; detachments from the metal d-orbitals all occur at low binding energies whereas those from the ligand-dominated orbitals all take place at rather high binding energies. We also found a remarkable correlation between electron affinities measured in vacuo and the redox potentials obtained in the solution phase of these species. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3635-3638 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A photodetachment photoelectron spectroscopy study of a doubly charged anion (S2O82−) in the gas phase is reported at three photon energies: 193, 266, 355 nm. Adiabatic and vertical electron binding energies of S2O82− were measured to be 1.7±0.2 and 2.2±0.1 eV, respectively. Several excited states were observed for the S2O8− singly charged anion at 193 nm. The repulsive Coulomb barrier that binds multiply charged anions was clearly shown in the detachment spectra of S2O82−. The effects of the Coulomb barrier to the detachment spectra and electron tunneling through the barrier are presented. The barrier height, which is equivalent to the magnitude of the Coulomb repulsion between the two excess charges in S2O82− was estimated to be ∼3 eV. © 1999 American Institute of Physics.
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