ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
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
    Vibrational frequencies of the HF dimer from the coupled cluster method including all single and double excitations plus perturbative connected triple excitations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6051-6056 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dissociation energies, equilibrium structures, equilibrium dipole moments, harmonic vibrational frequencies, infrared (IR) intensities, and zero-point vibrational energies (ZPVEs) are presented for the hydrogen fluoride monomer and dimer at the coupled cluster with single and double excitations plus perturbative connected triple excitations [CCSD(T)] level of theory with a series of large basis sets. Discussion focuses on the results from the largest basis set, triple zeta plus double polarization and one set of higher angular momentum functions [TZ2P(f,d)]. The structural parameters and dissociation energy agree well with the recent theoretical values reported in a high level ab initio study by Peterson and Dunning [J. Chem. Phys. 102, 2032 (1995)] and with experimental results. Here, the harmonic vibrational frequencies and IR intensities for the dimer are also predicted. The predicted vibrational frequency shifts relative to the monomer for the HF and DF stretching coordinates in the dimer are close to the experimental estimates. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470433
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    An ab initio study on the ground state HBO–BOH system (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1280-1287 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio electronic structure theory has been employed in order to investigate the ground state potential energy hypersurfaces of the HBO–BOH system. Geometries, dipole moments, harmonic vibrational frequencies, and infrared intensities of two equilibrium and two transition state [inversion (bending through linear geometry) and isomerization] structures were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using three basis sets. The theoretically predicted geometries and physical properties agree very well with available experimental values. At the highest level of theory employed in this study, CCSD(T) using triple zeta plus double polarization with higher angular momentum function [TZ2P(f,d)] basis set, the linear HBO molecule is predicted to be 45.0 kcal/mol more stable relative to the bent BOH species; with the zero-point vibrational energy (ZPVE) correction this energy separation becomes 44.4 kcal/mol; the classical barrier height for the inversion motion of the bent BOH molecule is predicted to be 3.5 kcal/mol and the barrier height with the ZPVE correction is 3.0 kcal/mol; the classical activation energy for the isomerization (1,2 hydrogen shift) reaction BOH→HBO is determined to be 29.4 kcal/mol and the activation energy with the ZPVE correction is 26.6 kcal/mol. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468916
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The GeOH+–HGeO+ system: A detailed quantum mechanical study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7975-7982 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state potential energy hypersurface of the GeOH+–HGeO+ system has been investigated employing ab initio electronic structure theory. First, geometries of two equilibrium and isomerization (1,2 hydrogen shift) reaction transition state were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using four basis sets. A qualitatively incorrect geometry is predicted for GeOH+ unless f functions are included in the basis set. Second, physical properties including dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities of three stationary points were evaluated at the optimized geometries. The effects of electron correlation reduce the dipole moment of HGeO+ by 1.25 Debye. At the highest level of theory employed in this study, CCSD(T) using the triple zeta plus double polarization with diffuse and higher angular momentum functions [TZ2P(f,d)+diff] basis set, linear GeOH+ is predicted to be more stable than linear HGeO+ by 71.7 kcal/mol. After correction for zero-point vibrational energies (ZPVEs), this energy difference becomes 70.3 kcal/mol. With the same method the classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HGeO+→GeOH+ is determined to be 30.3 kcal/mol and the activation energy (with the ZPVE correction) is 28.0 kcal/mol. The predicted dipole moments of GeOH+ and HGeO+ are 0.61 and 4.64 Debye, respectively. Thus, the HGeO+ ion may be suitable for a microwave spectroscopic investigation. On the other hand, the GeOH+ ion may be suitable for an IR spectroscopic study due to the strong IR intensities of the three vibrational modes. The geometrical and energetic features are compared with those of the valence isoelectronic HCO+–COH+ and SiOH+–HSiO+ systems. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470215
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The SiOH+–HSiO+ system: A high level ab initio quantum mechanical study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5327-5334 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio electronic structure theory has been employed in order to investigate the ground state potential energy hypersurface of the SiOH+–HSiO+ system. Geometries and physical properties including dipole moments, harmonic vibrational frequencies, and infrared intensities of two equilibrium and isomerization (1,2 hydrogen shift) reaction transition state were determined. The self-consistent-field, configuration interaction with single and double excitations, coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory were used with five basis sets. At the highest level of theory employed in this study, CCSD(T) using the triple zeta plus double polarization with diffuse and higher angular momentum functions basis set, linear SiOH+ is predicted to be more stable than linear HSiO+ by 66.1 kcal/mol. This energy difference becomes 64.1 kcal/mol with an appropriate zero-point vibrational energy (ZPVE) correction. At the same level of theory, the classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HSiO+→SiOH+ is determined to be 29.3 kcal/mol and the activation energy (with the ZPVE correction) is 27.3 kcal/mol. The geometrical and energetic features are compared with those of the valence isoelectronic HBO–BOH, HCO+–COH+, and AlOH–HAlO systems. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469259
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The SiOH–HSiO system: A high level quantum mechanical study (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1951-1958 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy hypersurface of the SiOH–HSiO system has been investigated using ab initio electronic structure theory. The geometries and physical properties including dipole moments, harmonic vibrational frequencies, and associated infrared (IR) intensities for the two equilibrium and isomerization (1,2 hydrogen shift) transition state structures have been determined employing self-consistent-field (SCF) and configuration interaction with single and double excitations (CISD) methods. At the CISD optimized geometries, single point energies of the three stationary points were evaluated using coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)] levels of theory. In the correlated procedures three different frozen core schemes (6 frozen core, 2 frozen core, and 0 frozen core) have been applied to examine the importance of 1s, 2s, and 2p core electrons. With the SCF method two isomers (A and B) were found for HSiO. However, at the CISD level of theory structure B with the bond angle of about 93° has collapsed to structure A with the bond angle of about 122°, confirming the findings of lower level studies. At the highest level of theory, CCSD(T) with triple zeta plus double polarization (TZ2P) augmented with higher angular momentum and diffuse functions TZ2P(f,d)+diff basis set, TZ2P(f,d)+diff CCSD(T), the energy separation between SiOH and HSiO is predicted to be 12.1 kcal/mol. This energy separation becomes 9.8 kcal/mol with the zero-point vibrational energy (ZPVE) correction. With the same method the classical energy barrier for the exothermic isomerization reaction (HSiO→SiOH) was determined to be 25.8 kcal/mol and the activation energy (with the ZPVE correction) becomes 24.1 kcal/mol. The two frozen core approximations have generated 0.005 A(ring) (6 frozen core) and 0.001 A(ring) (2 frozen core) in error for the SiO bond length compared to no frozen core method. In energetics these two frozen core schemes have produced errors of ±0.40 kcal/mol for the CCSD and CCSD(T) methods and error of ±0.95 kcal/mol for the CISD method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472064
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    The GeOH–HGeO system: Are the 3d electrons core or valence? (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9841-9847 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 2A′ ground state of GeOH–HGeO system has been investigated by ab initio electronic structure theory. The equilibrium geometries and physical properties including dipole moments, harmonic vibrational frequencies, and associated infrared (ir) intensities for GeOH, HGeO, and the isomerization (1,2 hydrogen shift) transition state are determined at the self-consistent-field (SCF) and configuration interaction with single and double excitations (CISD) levels of theory with four basis sets. There appear to be two minima for the bent HGeO (isomers A and B) on its SCF and CISD potential energy hypersurfaces. At the Hartree–Fock level the structure with HGeO angle near 90° (isomer B) lies lower, but correlated methods show that the structure with HGeO angle near 120° (isomer A) actually lies lower. At the optimized CISD geometries, the single point energies of coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)] methods are also determined. In the correlated procedures three different types of frozen core orbital approximation (15 frozen core, 10 frozen core, and 6 frozen core orbitals) have been examined. The energetics based on the first (15 frozen core orbitals) approximation present errors of about 1 kcal/mol compared to more accurate second (10 frozen core orbitals) and third (6 frozen core orbitals) approximations. At the highest level of theory employed in this research, CCSD(T) with triple zeta plus double polarization with diffuse and higher angular momentum functions [TZ2P(f,d)+diff] basis set, the bent GeOH molecule is predicted to be lower in energy than the bent HGeO molecule by 28.5 kcal/mol. This energy separation becomes 25.7 kcal/mol with the zero-point vibrational energy (ZPVE) correction. The classical energy barrier for the exothermic isomerization reaction [HGeO(B)→GeOH] is determined to be 11.8 kcal/mol and the activation energy (with the ZPVE correction) 10.7 kcal/mol. The theoretically predicted isotope shifts for the GeO stretching vibrational frequency of GeOH agree very well with experimental assignments by Withnall and Andrews [J. Phys. Chem. 94, 2351 (1990)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471743
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    The A˜ 1Au state and the T2 potential surface of acetylene: Implications for triplet perturbations in the fluorescence spectra of the A˜ state (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8507-8515 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The cis–trans isomerization reaction on the T2 surface of acetylene and the lowest excited singlet state of acetylene, A˜ 1Au, are investigated by ab initio electronic structure theory. We report optimized geometries, dipole moments, and harmonic vibrational frequencies of stationary points and adiabatic energy differences between them using basis sets as large as triple-ζ plus double polarization with higher angular momentum functions, TZ(2df,2pd), and theoretical methods up to coupled-cluster singles and doubles with a perturbative triples correction [CCSD(T)] and the equation-of-motion coupled-cluster method (EOM-CCSD). Our theoretical predictions should aid the interpretation of observations from a series of recent spectroscopic studies involving excited electronic states of acetylene. In particular, the present theoretical results rule out several possible explanations for the anomalous sudden increase in detectable Zeeman anticrossings reported by Dupré et al. [Chem. Phys. 152, 293 (1991)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471658
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    The GaOH–HGaO potential energy hypersurface and the necessity of correlating the 3d electrons (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8516-8523 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state potential energy hypersurface of the GaOH–HGaO system has been investigated using high level ab initio molecular electronic structure theory. The geometries and physical properties of two equilibrium structures, one isomerization transition state and one inversion transition state were determined at the self-consistent field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with four sets of basis functions. It has been found that freezing the 3d electrons of the Ga atom in the correlation procedures is not appropriate for this system. For the energy difference ΔE (GaOH–HGaO) the freezing of the 3d electrons results in an error of 25 kcal/mol! The dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities are predicted for the four stationary points. At the highest level of theory employed in this study, CCSD(T) using triple zeta plus double polarization with higher angular momentum and diffuse functions [TZ2P(f,d)+diff] basis set, the bent GaOH was found to be 41.9 kcal/mol more stable than the linear HGaO species; with the zero-point vibrational energy (ZPVE) correction, the energy separation becomes 40.4 kcal/mol. The classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HGaO→GaOH is determined to be 44.5 kcal/mol and the barrier height with the ZPVE correction 42.3 kcal/mol. The classical barrier to linearity for the bent GaOH molecule is determined to be 1.7 kcal/mol and the barrier height with the ZPVE correction to be 1.2 kcal/mol. The predicted dipole moments of GaOH and HGaO are 1.41 and 4.45 Debye, respectively. The effects of electron correlation reduce the dipole moment of HGaO by the sizable amount of 1.2 Debye. The two equilibrium species may be suitable for microwave spectroscopic investigation. Furthermore, they may also be detectable by IR techniques due to the relatively large intensities of their vibrational modes. The geometrical and energetic features are compared with those of the valence isoelectronic HXO–XOH systems, where X is a group IIIA atom and the HXO+–XOH+ systems, where X is a group IVA atom. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471763
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    The anomalous behavior of the Zeeman anticrossing spectra of A˜ 1Au acetylene: Theoretical considerations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1774-1778 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: P. Dupré, R. Jost, M. Lombardi, P. G. Green, E. Abramson, and R. W. Field have observed anomalous behavior of the anticrossing density in the Zeeman anticrossing (ZAC) spectra of gas phase A˜ 1Au acetylene in the 42 200 to 45 300 cm−1 energy range. To best explain this result, they hypothesize a large singlet–triplet coupling due to the existence of a linear isomerization barrier connecting a triplet-excited cis- and trans-acetylene in the vicinity of the studied energy range (∼45 500 cm−1). Theoretically such a linear stationary point, however, must have two different degenerate bending vibrational frequencies which are either imaginary or exactly zero. Neither case has yet been experimentally detected. Here, we have studied the two lowest-lying linear triplet-excited-state stationary points of acetylene, 3Σ+u and 3Δu, to see if they fit Dupré et al.'s hypothesis. We have completed geometry optimization and harmonic vibrational frequency analysis using complete-active-space self-consistent field (CASSCF) wave functions as well as determined energy points at those geometries using the second-order configuration interaction (SOCI) method. Harmonic vibrational analyses of both stationary points reveal two different doubly degenerate vibrational modes with imaginary vibrational frequencies (or negative force constants) indicating that they are indeed saddle points with a Hessian index of four. At the DZP SOCI//CASSCF level of theory with zero-point vibrational energy (ZPVE) correction, the 3Σ+u stationary point lies 35 840 cm−1 above the ground state of acetylene. This is much too low in energy to contribute to the ZAC spectral anomaly. At the same level of theory with ZPVE correction, the 3Δu stationary point lies 44 940 cm−1 above the ground state consistent with Dupré et al.'s hypothesis. Several solutions to the anomalous ZAC spectra are discussed. We propose that the anomaly may also be due to coupling with a nearly linear structure on the T3 surface of acetylene. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471646
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Dimethylcarbene: A Singlet Ground State? (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 10104-10107 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00145a023
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...