ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4763-4773 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Propargylene was identified in a matrix as a product of photolysis of cyclopropenylidene and diazopropyne. The molecule is a triplet. The optimum geometry predicted by ab initio calculations corresponds to a structure HC≡C–C¨H. The transition structure in the interconversion HC≡C–C¨H(arrow-right-and-left)HC(overdot)=C=C(overdot)H(arrow-right-and-left)HC¨–C≡CH is very low in energy and close to the energy of the vibrational ground state. Owing to this nonrigidity, computed infrared (IR) frequencies based on a harmonic treatment do not match the experimental spectrum. When this nonrigidity is taken into account by using a nonharmonic approximation calculated UMP2/6-31G** IR spectra are in good agreement with the observed spectra of HCCCH and DCCCD.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 703-710 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The behavior of various contributions to the f↔f transition amplitude defined up to the third order in perturbation theory is analyzed. Main attention is paid to the third-order contributions which are due to electron correlation inside the rare earth ion and arise from the static and dynamic models. The discussion is based on the numerical results of exact ab initio calculations performed for Pr+3, Nd+3, Eu+3, Gd+3, Tb+3, and Tm+3 ions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8693-8702 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical relaxation of the N2O4 dissociation was studied using Ar+ laser excited acoustic resonances of a cylindrical cavity. The resonance profiles of the first radial mode were measured as a function of pressure and temperature by a computer controlled setup. The N2O4 dissociation rate constant and the mean rotational and vibrational relaxation time of the N2O4–NO2 mixture were obtained for temperatures between 273 and 317 K by fitting a detailed theoretical model of the resonator to the measured values for frequency dispersion, resonance broadening, and strength of the photoacoustic signal. Excellent agreement between theory and experiment was obtained for the frequency dispersion and the photoacoustic signal. An empirical correction function had to be introduced to account for discrepancies between the theoretically predicted and measured values of the resonance broadening which was in the percent region. A value of 6.1×10−15 cm3/molecule s was determined for the rate constant of N2O4 dissociation in the low pressure limit at 298 K. The activation energy of the N2O4 dissociation for 20 mbar pressure was determined to be EA=36 kJ/mol. A comparison of the measured low-pressure limit of the unimolecular rate constant with theoretical predictions of RRKM theory yielded values for the mean collision efficiency of N2O4 and NO2 between 0.95 and 0.5 in the temperature range 273–317 K.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1390-1395 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The third-order electron-correlation theory of two-photon absorption in rare earth ions in crystals has been extended by the effective operators arising from doubly excited configurations. The approach defined in terms of one-particle effective operators has been applied to the Pr+3, Nd+3, Eu+3, Gd+3, Tb+3, and Tm+3 ions. The relative importance of third-order contributions and their properties across the lanthanide series are presented. The discussion is based on the numerical results of exact ab initio calculations performed within the perturbed-function approach.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 411-415 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that intermediate arrays resulting from the quasilinearization of coupled-cluster theory with double excitations, and having the form of pseudointegrals 〈ab||ij〉n, retain symmetry properties of the ordinary two-electron integrals 〈ab||ij〉. The 〈ab||ij〉n elements vanishing on symmetry grounds may be eliminated a priori, as well as contributions to nonvanishing 〈ab||ij〉n pseudointegrals from vanishing 〈ab||ij〉n−1 or 〈ab||ij〉 terms. A program using molecular symmetry in this way has been coded and its speed compared with that of gaussian 82.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3773-3780 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute I* quantum yields have been measured as a function of wavelength for room temperature photodissociation of the ICN A˜ state continuum. The yields are obtained by the technique of time-resolved diode laser gain-vs-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0±2% and it falls off to 53.4±2% and 44.0±4% at 284 and 248 nm, respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I* quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I* yields reported here. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I* quantum yield results.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3950-3958 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pulsed photothermal generation and probe-beam deflection technique was applied to monitor nonradiative relaxation and transport processes in CS2 and in NO2–N2O4 vapors following nitrogen laser excitation at 337.1 nm. A theoretical model is developed to describe the signal shape, and to derive the thermal diffusivity and energy relaxation time. The experiments were performed over a vapor pressure range of typically 1–100 Torr with a time resolution of 1 μs. In CS2 vapor of pressure above 10 Torr at room temperature, a slow heat release component is observed attributed to the photochemical formation of (CS)n particulates ("laser-snow''). In NO2–N2O4 vapor, the experimental data provide the thermal diffusivity values in the pressure range of 1–100 Torr; these measurements support a "frozen equilibrium'' model and indicate that any contribution due to the diffusional transport of chemical enthalpy for this system is small in this pressure range at room temperature. These experiments demonstrate that the photothermal probe-beam deflection technique can provide useful information on heat-release rates, for example, due to particulate formation, as well as measurement of thermal diffusivity, for example, in hostile and dissociative gas systems.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3366-3370 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A single line UV Ar++ laser has been used for the photochemical production of NaCd and NaHg excimers, detected by their characteristic bound–free emission in the blue spectral region. Selected laser lines excited specific levels in the C 1Πu electronic state of the Na2 molecule. The chemical reaction of the excited sodium dimer with Cd or Hg atoms produced NaCd and NaHg excimers. We suggest a simple model for the explanation of the observed spectra, based on recent ab initio theoretical calculations.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6049-6060 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method of deriving explicit formulas for the calculation of second-order exchange contributions (induction as well as dispersion) within the framework of symmetry-adapted perturbation theories is presented. It is shown how exchange contributions can be expressed as a combination of electrostatic interaction energies between suitably generalized charge distributions (overlap intermolecular charge distributions). Each of these contributions are derived within the Hartree–Fock approximation (neglect of all electron correlation effects within the noninteracting molecules) and by considering only single-electron exchange between interacting molecules. Numerical calculations for the interaction of two water molecules are presented. In the region of the equilibrium geometry, it is found that the complete second-order exchange contribution accounts for about 20% of the total intermolecular interaction energy. This contribution is essentially dominated by the exchange induction component which is found to represent approximately 1 kcal/mol (using a basis set containing 94 orbitals). To our knowledge, this is the first example of calculation of exchange induction interaction energy for a molecular system. Concerning the less important, but non-negligible, exchange dispersion component, our result is found to agree with a very recent calculation for the water dimer.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6069-6076 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Variational calculations of vibrational levels of three Ag modes are reported for cyclobutadiene, its vicinally 13C-dilabeled derivative, and the tetralabeled derivatives 13C4H4 and C4D4. These calculations use the ab initio two-configuration GVB/4-31G potential surface for the antisymmetric CC stretch (automerization), symmetric CC stretch, and symmetric CCH bend. The three vibrational modes are strongly coupled so that one-dimensional and adiabatic multidimensional approaches are not justifiable in this case. The splitting of the ground vibrational state of di-13C -cyclobutadiene is calculated to be 4 cm−1, which implies the rate constant for automerization is k=2.4×1011 s−1 at temperatures near absolute zero. The Raman spectrum of cyclobutadiene is predicted to have two strong bands in the region of 3100–3200 cm−1. The other transitions are predicted to be of considerably lower intensity, though three of them should be strong enough to be observed. Two of the three are predicted to be accompanied by satellite lines which are due to the automerization splitting of the Ag levels. Uncertainties involved in the theoretical approach are discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...