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  • 1
    Electronic Resource
    Electronic Resource
    Photoelectron spectroscopy and electronic structure of clusters of the group V elements. II. Tetramers: Strong Jahn–Teller coupling in the tetrahedral 2E ground states of P+4, As+4, and Sb+4 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6318-6326 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution HeI (584 A(ring)) photoelectron spectra have been obtained for the tetrameric clusters of the group V elements: P4, As4, and Sb4. The spectra establish that the ground 2E states of tetrahedral P+4, As+4, and Sb+4 are unstable with respect to distortion in the ν2(e) vibrational coordinate. The E⊗e Jahn–Teller problem has been treated in detail, yielding simulated spectra to compare with experimental ones. Vibronic calculations, extended to second order (quadratic coupling) for P+4, account for vibrational structure which is partially resolved in its photoelectron spectrum. A Jahn–Teller stabilization energy of 0.65 eV is derived for P+4, which can be characterized in its ground vibronic state as being highly distorted, and highly fluxional. Linear-only Jahn–Teller coupling calculations performed for As+4 and Sb+4, show good qualitative agreement with experimental spectra, yielding stabilization energies of 0.84 and 1.4 eV, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459698
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  • 2
    Electronic Resource
    Electronic Resource
    Photoelectron spectroscopy and electronic structure of clusters of the group V elements. III. Tetramers: The 2T2 and 2A1 excited states of P+4, As+4, and Sb+4 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6327-6333 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Methods employing high resolution HeI (584 A(ring)) photoelectron spectroscopy have been applied to the tetrameric clusters of the group V elements, to resolve details of vibronic and spin–orbit structure in the first three electronic states of P+4, As+4, and Sb+4. Measured spacings of distinct vibrational progressions in the ν1 mode for the 2A1 states of P+4 and As+4, yield vibrational frequencies of 577 (5) cm−1 for P+4 and 350 (6) cm−1 for As+4. Franck–Condon factor calculations suggest bond length changes for the ions in the 2A1 states of 0.054 (3) A(ring) for P+4 and 0.060 (3) A(ring) for As+4. Strong Jahn–Teller distortions in the ν2(e) vibrational mode dominate the structure of the 2E ground states of the tetrameric ions. Both Jahn–Teller and spin–orbit effects appear in the spectra of the 2T2 states of the tetrameric ions, with the spin–orbit effect being dominant in Sb+4 and the Jahn–Teller effect dominant in P+4. Vibrational structure is resolved in the P+4 spectrum, and the ν3(t2) mode is found to be the one principally active in the Jahn–Teller coupling. A classical metal-droplet model is found to fit well with trends in the IPs of the clusters as a function of size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458975
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  • 3
    Electronic Resource
    Electronic Resource
    Jet-resolved vibronic structure in the higher excited states of N2O: Ultraviolet three-photon absorption spectroscopy from 80 000 to 90 000 cm−1 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3916-3925 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ionization-detected ultraviolet multiphoton absorption spectroscopy reveals Rydberg structure in the excited states of N2O within 20 000 cm−1 of the first ionization threshold. This structure persists, with atomic-like quantum defects and vibrational structure well matched with that of the ion, despite evidence for coupling of vibrationally excited Rydberg states with the underlying valence continuum. In the most completely resolved spectrum, which is assigned to the 3pσ 1Π state, hot-band, fundamental and overtone transitions involving the bending mode ν2, indicate Renner–Teller and Herzberg–Teller coupling of electronic and vibrational angular momentum. Vibronic intensities and positions suggest that these couplings can be regarded as properties of the N2O+ ion core, mirroring behavior manifested in the electronic emission spectrum of the ion. Window resonances are observed in the ionization-detected absorption spectrum above the four-photon ionization threshold, which are assigned to vibrationally excited Rydberg states that couple to competing continuua in which predissociation dominates Δv=−1 vibrational autoionization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456823
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  • 4
    Electronic Resource
    Electronic Resource
    A nomenclature for Λ-doublet levels in rotating linear molecules (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1749-1753 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is proposed that the two Λ-doublet levels of linear molecules with nonzero electronic orbital angular momentum be labeled Λ(A') and Λ(A‘), e.g., Π(A') and Π(A‘) for Π states, etc., according to the following prescription: All series of levels in which the electronic wave function at high J is symmetric with reflection of the spatial coordinates of the electrons in the plane of rotation will be designated Λ(A') for all values of J, and all those for which the electronic wave function is antisymmetric with respect to reflection will be denoted Λ(A‘). It is emphasized that this notation is meant to supplement, and not replace, the accepted spectroscopic e/f labeling and the parity quantum number. The utility of the Λ(A')/Λ(A‘) notation is that it is of most relevance in the mechanistic interpretation of reactive or photodissociative processes involving open-shell molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455121
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  • 5
    Electronic Resource
    Electronic Resource
    Higher excited states of benzene: Polarized ultraviolet two-photon absorption spectroscopy (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1115-1134 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Rydberg spectrum of benzene is explored by means of linear and circular polarized ultraviolet two-photon absorption spectroscopy of the jet-cooled molecule. A strong gerade Rydberg series previously designated nRg and all its associated vibronic structure seen in linear polarization is shown to have symmetry A1g, but analysis of spectra obtained under circular polarization demonstrates that E2g origins lie just to lower energies. These combined facts give an unambiguous assignment of this series as nd1 (E2g, A1g, A2g). Four new Rydberg series, each having vibrational structure nearly identical to each other and to the ground state ion, are also identified and have E1g or E2g symmetry. The five Rydberg series converging to the first ionization potential have quantum defects 0.77, 0.06, 0.05, 0.02, and −0.11. Bandwidths indicative of ultrafast radiationless decay processes are observed for low-n vibronic states, but higher states are sharp. In addition, an Eg band system is observed at 68 980 cm−1 (69 330 for C6D6) whose term value, vibrational structure, bandwidth, and isotope shift on deuteration are all consistent with its assignment as the lowest Rydberg state converging to the first excited ionic state (second ionization potential).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448484
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  • 6
    Electronic Resource
    Electronic Resource
    Higher excited states of benzene: Symmetry assignments of six gerade Rydberg series by four-photon absorption spectroscopy (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1135-1146 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the observation of six gerade Rydberg series in benzene converging to the first ionization potential, seen in the region from 14 500–18 500 cm−1 as four-photon resonances in the five-photon ionization spectrum of the jet-cooled molecule. Polarization ratios measured for each transition in two- as well as four-photon resonance aid in determining excited state symmetries. We assign a Rydberg series with a quantum defect of 0.76 to higher members of the 3s Rydberg state first seen by Johnson in the near UV two-photon resonant three-photon ionization spectrum of benzene. The observed quantum defect, polarization ratios, and correlation with synchrotron absorption data all strongly support this assignment. Another series, with a quantum defect of 0.24, exhibits a polarization ratio of 4.5±0.5 signifying pure rank four activity. This is the first report of a purely rank four transition in a molecule. We assign this as an excitation to a d2 orbital which when converging to the first ionization potential (the 2E1g cation) gives rise to B1g and B2g Rydberg transitions. Within the D6h point group, these symmetries are allowed only in a four-photon transition. The number of gerade Rydberg series observed as four-photon resonances exceeds those available from the s-(1) and d-(3) bound members of a hydrogenic basis set. The participation of g(l=4) orbitals is indicated as the lowest members of two of the Rydberg series are at the n=5 level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448485
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  • 7
    Electronic Resource
    Electronic Resource
    Laser-assisted (1+1′)-photon ionization-detected absorption spectrum of the 3pπ 2Π state of HCO and DCO (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 8384-8395 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We re-examine the ionization-detected ultraviolet absorption spectrum of the 3pπ 2Π←X 2A′ transition in HCO and DCO using a high-power visible laser to enhance the observation of first-photon resonant features. This technique, which we term here, assisted REMPI, significantly improves the signal-to-noise ratio of the spectrum, making many weak vibronic sub-bands visible for the first time. A comprehensive fit to the structure evident in a progression of bending levels from (000) to (040) refines the assignment of Song and Cool [X. M. Song and T. A. Cool, J. Chem. Phys. 96, 8664 (1992)] to yield a set of rotational constants that vary with K in relation to v2, together with a higher-order contribution to the Renner–Teller splitting in HCO, which is mirrored in DCO for all levels but (040). The (040) band falls at a frequency that is commensurate with that of CD stretch, and Fermi resonance between 3pπ 2Π(1000)Π and the higher-energy (040) K=1(Π) component gives rise to an added splitting that increases the energy of this (040) component and causes an apparent increase in the Renner parameter. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467329
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  • 8
    Electronic Resource
    Electronic Resource
    Spin–orbit autoionization and intensities in the double-resonant delayed pulsed-field threshold photoionization of HCl (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8633-8640 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-selected delayed pulsed-field threshold photoionization spectra of HCl and DCl are recorded in double-resonant transitions through the F 1Δ, E 1Σ+, and g 3Σ− states of the 4pπ Rydberg configuration. Comparison of observed rotational line strengths with calculated spectra, as well as with available time-of-flight photoelectron spectra, provides useful insight on the influence of spin–orbit and rotational autoionization on delayed pulsed-field threshold photoionization of HCl. Spin–orbit and rotational autoionization are seen to dramatically reduce the ion rotational intensity associated with the upper spin–orbit level of the ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466717
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  • 9
    Electronic Resource
    Electronic Resource
    On the assignment of Jahn–Teller effects in the ultraviolet absorption spectrum of Ag3 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6312-6317 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Jahn–Teller linear-plus-quadratic Hamiltonian is shown to account for most of the observed band positions and intensities in the absorption and emission spectra of Ag3. Coupling parameters obtained for a simultaneous fit to absorption and emission results are k=1.93, g=0.25 for the E' ground state and k=0.19, g=0.02 for the E‘ excited state. At higher vibrational energies, simple Jahn–Teller calculations predict fewer bands than observed. Calculations including spin–orbit coupling with larger linear coupling partially quenched by the Ham effect offer a reasonable explanation for this higher energy structure. Splittings and intensity sharing at lower vibrational energies, however, demand higher-order Jahn–Teller coupling, indicating the need for more extensive calculation simultaneously incorporating quadratic Jahn–Teller effects, spin–orbit coupling, and perhaps anharmonicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467093
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  • 10
    Electronic Resource
    Electronic Resource
    High-resolution threshold photoionization of N2O (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 746-753 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Pulsed field ionization (PFI) has been used in conjunction with a coherent vuv source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N2O+ cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham–Orr–Sichel equations [A. D. Buckingham, B. J. Orr, and J. M. Sichel, Philos. Trans. R. Soc. London, Ser. A 268, 147 (1970)] using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of the outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core. The PFI technique also allows us to report an improved value for the ionization potential of N2O of 103 963±5 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461080
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