ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Two-Electron Aromatics with Classical and Non-Classical Homobridges (2000)

Hofmann, Matthias ; Scheschkewitz, David ; Ghaffari, Abolfazl ; [et al.]

Springer

Journal of molecular modeling 6 (2000), S. 257-271

add to mindlist on the mindlist

Details

ISSN: 0948-5023

Keywords: KeywordsAb initio, Boron compounds, Crystal structure, Homoaromatics, Three center two electron bond

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract Bishomotriborirane anions with a B-H-B bridge, 7, have been synthesized by a) protonation and b) methylation of bishomodianions, 3, as well as by c) hydride addition to 1,2,4-triboracyclopentanes, 15. Compounds 7 were characterized by 1H, 13C and 11B NMR spectroscopy and X-ray diffraction analyses. The suggested mechanism for the formation of 7 is supported by MP4SDTQ/6-311++G**//MP2(fc)/6-31+G* computations on [C2B3H8]- model compounds. Classical 1,2-dibora-4-borata-cyclopentane intermediates 16 undergo an intramolecular hydrogen shift to the B-B unit in their envelope conformation to give intermediates 17, which easily isomerize to 7. Relative energies for the parent compounds, 16u, 17u, 7u and the transition structures, TS-16/17u and TS-7/17u are predicted to be 30.7, 14.5, 0.0, 32.6 and 23.5 kcal mol-1, respectively. The terms classical and non-classical homobridges are suggested for methylene and hydrogen bridges in 7 and in related compounds on the grounds of common building principles. The strength of homoaromaticity in 7u was estimated to be at least 23.5 kcal mol-1, neglecting the much higher strain in 7u compared to TS-7/17u without a 3c2e bond.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s0089400060257

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

2

Electronic Resource

The 3A2, 1A2, 3B2, and 1B2 electronic states of CH2: Small bond angle states (1997)

Yamaguchi, Yukio ; Schaefer III, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 1819-1826

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Molecular structures with very small bond angles are a curiosity in chemistry. The two triplet (3A2 and 3B2) and two singlet (1A2 and 1B2) excited states of CH2 have been investigated systematically using ab initio electronic structure theory. For these four states total energies and physical properties including geometries, dipole moments, harmonic vibrational frequencies, and associated infrared intensities were determined with the single and double excitation configuration interaction (CISD) method using four different basis sets. It is confirmed in this study that the four states of CH2 all have bent structures with longer CH bond lengths and smaller bond angles than the four lower-lying (X˜, a˜, b˜, and c˜) states of CH2. At the CISD optimized geometries single point energies were determined with complete active space self-consistent-field (CASSCF) and CASSCF second-order configuration interaction (SOCI) levels of theory. For the triplet excited states single point energies were also determined employing coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitations methods. At the CISD level with the largest basis set, the triple zeta plus triple polarizations with two sets of higher angular momentum and two sets of diffuse functions basis set [TZ3P(2 f,2d)+2diff], the bond angles were predicted to be 40.6° (3A2), 46.1° (1A2), 76.3° (3B2), and 81.3° (1B2), while the dipole moments were determined to be 2.35 (3A2), 2.26 (1A2), 1.69 (3B2), and 1.60 debye (1B2), respectively. With the most accurate method in this study, the CASSCF-SOCI level with the TZ3P(2 f,2d)+2diff basis set, the energy separations (Te value) between the ground state (X˜ 3B1) and the four excited states were predicted to be 73.7 kcal/mol (3.20 eV, 25 800 cm−1) for the 3A2 state, 96.8 kcal/mol (4.20 eV, 33 800 cm−1) for the 1A2 state, 151.0 kcal/mol (6.55 eV, 52 800 cm−1) for the 3B2 state, and 182.5 kcal/mol (7.91 eV, 63 800 cm−1) for the 1B2 state, respectively. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473323

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

3

Electronic Resource

The weakly bound dinitrogen tetroxide molecule: High level single reference wavefunctions are good enough (1997)

Wesolowski, Steve S. ; Fermann, Justin T. ; Crawford, T. Daniel ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 7178-7184

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Ab initio studies of dinitrogen tetroxide (N2O4) have been performed to predict the equilibrium geometry, harmonic vibrational frequencies, and fragmentation energy (N2O4→2 NO2). The structure was optimized at the self-consistent field, configuration interaction, and coupled-cluster levels of theory with large basis sets. At the highest level of theory, the N–N bond distance was 1.752 Å, in excellent agreement with the experimental value of 1.756±0.01 Å. In addition, the harmonic vibrational frequencies were predicted with an average absolute error of 51 cm−1 relative to experimental fundamental values with differences largely attributed to anharmonic effects. The fragmentation energy corrected for zero point vibrational energy and basis set superposition error was 7.2 kcal/mol, in fair agreement with the experimental value of 12.7 kcal/mol. Despite the suggestion that a multireference wavefunction may be necessary to accurately describe the biradical nature of N2O4, single reference treatments with large basis sets and high levels of electron correlation yield molecular parameters remarkably close to experimental values.© 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473679

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

4

Electronic Resource

Revision of the experimental electron affinity of BO (1997)

Rienstra, Jonathan C. ; Schaefer III, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 8278-8279

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The experimental electron affinity of BO has proven questionable. We obtained the electron affinity of BO using the large aug-cc-pVQZ basis with SCF, CISD, CISD+Q, CCSD, and CCSD(T) methods and predict a value of 2.57 eV, or 0.55 eV smaller than the latest experimental value. The 2∑+ to 2Π excitation energy of BO has also been obtained with the CCSD(T) method and found to be 2.82 eV. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473799

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

5

Electronic Resource

A high level theoretical investigation of the cyclic hydrogen fluoride trimer (1997)

Tschumper, Gregory S. ; Yamaguchi, Yukio ; Schaefer III, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 9627-9633

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: A high level ab initio theoretical investigation of the cyclic hydrogen fluoride trimer was carried out. The structures of the hydrogen fluoride monomer, dimer, and trimer were fully optimized at the coupled-cluster level of theory including single, double, and perturbatively applied connected triple excitations [CCSD(T)] using three large basis sets. Geometrical parameters, dipole moments, harmonic vibrational frequencies, infrared intensities, and total energies are reported for each equilibrium structure. Changes in bond lengths and shifts in HF stretching frequencies relative to the monomer, as well as the dissociation energies corresponding to various fragmentation pathways, are given for the dimer, trimer, and their deuterated isotopomers. The theoretical results presented here are compared to the available experimental data and to those obtained from empirically refined potential energy surfaces. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473861

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

6

Electronic Resource

The 3d Rydberg (3A2) electronic state observed by Herzberg and Shoosmith for methylene (1997)

Yamaguchi, Yukio ; Schaefer III, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 8753-8759

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: In 1959 and 1961 Herzberg and Shoosmith reported the vacuum ultraviolet spectrum of the triplet state of CH2. The present study focuses on a characterization of the upper state, the 3d Rydberg (3A2) state, observed at 1415 Å. The theoretical interpretation of these experiments is greatly complicated by the presence of a lower-lying 3A2 valence state with a very small equilibrium bond angle. Ab initio electronic structure methods involving self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), complete active space (CAS) SCF, state-averaged (SA) CASSCF, coupled cluster with single and double excitations (CCSD), CCSD with perturbative triple excitations [CCSD(T)], CASSCF second-order (SO) CI, and SACASSCF-SOCI have been employed with six distinct basis sets. With the largest basis set, triple zeta plus triple polarization with two sets of higher angular momentum functions and three sets of diffuse functions TZ3P(2 f,2d)+3diff, the CISD level of theory predicts the equilibrium geometry of the 3d Rydberg (3A2) state to be re=1.093 Å and θe=141.3 deg. With the same basis set the energy (Te value) of the 3d Rydberg state relative to the ground (X˜ 3B1) state has been determined to be 201.6 kcal mol−1 (70 500 cm−1) at the CCSD (T) level, 200.92 kcal mol−1 (70 270 cm−1) at the CASSCF-SOCI level, and 200.89 kcal mol−1 (70 260 cm−1) at the SACASSCF-SOCI level of theory. These predictions are in excellent agreement with the experimental T0 value of 201.95 kcal mol−1 (70 634 cm−1) reported by Herzberg. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473935

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

7

Electronic Resource

The hydroperoxyl radical dimer: Triplet ring or singlet string? (1997)

Fermann, Justin T. ; Hoffman, Brian C. ; Tschumper, Gregory S. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 5102-5108

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: In order to determine the lowest energy isomer of the hydroperoxyl radical dimer, H2O4, ab initio quantum mechanical methods were employed to predict the geometrical structures, relative energies, harmonic vibrational frequencies, and associated IR intensities of both open chain and cyclic isomers. Two minima were located on the open chain potential energy surface, one of C2 symmetry and one of C1 symmetry. The relative energies of the different H2O4 structures vary strongly with level of theory. The most reliable treatment used in the present study predicted that the global minimum is the closed-shell C1 chain isomer which is lower in energy than the planar C2h triplet cyclic isomer by 1.6 kcal mol−1 including zero point vibrational energy corrections. It is argued that both structures should be observable, depending on the method of preparation. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473530

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

8

Electronic Resource

The ClO4 radical: Experiment versus theory (1997)

Van Huis, Timothy J. ; Schaefer III, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 4028-4037

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The chlorine tetroxide radical and its anion have been investigated with unrestricted Hartree–Fock, density functional and hybrid Hartree–Fock/density functional methods, perturbation theory, and coupled cluster methods. It is predicted that the minimum on the ClO4 radical potential energy surface corresponds to the 2B2 ground electronic state, a C2v-symmetry structure. The C3v structure identified experimentally lies a few kcal mol−1 higher energetically. A Cs symmetry structure lies very close energetically to the C2v minimum at some levels of theory. Adiabatic electron affinities, equilibrium geometries, harmonic vibrational frequencies, infrared intensities, isotopic shifts, and dipole moments are presented for all methods. Comparisons with recent experimental vibrational data for the radical are made. It is predicted that the C2v equilibrium geometry of the ground state is Re(Cl–O1)=1.502 Å, Re(Cl–O2)=1.424 Å, θe1=93.6° and θe2=114.2°. The adiabatic electron affinity of the ClO4 radical is predicted to lie near 5.2 eV. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.473121

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

9

Electronic Resource

The X˜1A1, a˜3B1, a˜1B˜1, and B˜1A1 electronic states of SiH2 (1997)

Yamaguchi, Yukio ; Van Huis, Timothy J. ; Sherrill, C. David ; [et al.]

Springer

Theoretical chemistry accounts 97 (1997), S. 341-349

add to mindlist on the mindlist

Details

ISSN: 1432-2234

Keywords: Key words: CASSCF ; SOCI ; Equilibrium geometries ; Excited states ; Vibrational frequencies ; IR intensities

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract. Four electronically low-lying states of silylene (SiH2) have been studied systematically using high level ab initio electronic structure theory. Self-consistent field (SCF), two-configuration (TC) SCF, complete active space (CAS) SCF, configuration interaction with single and double excitations (CISD), and CASSCF second-order (SO) CI levels of theory were employed with eight distinct basis sets. The zeroth-order wave functions of the ground (X˜ 1A1 or 1 1A1) and B˜ 1A1 (or 2 1A1) excited states are appropriately described by the first and second eigenvectors of the TCSCF secular equations. The TCSCF-CISD, CASSCF, and CASSCF-SOCI wave functions for the B˜ 1A1 (or 2 1A1) state were obtained by following the second root of the CISD, CASSCF, and SOCI Hamiltonian matrices. At the highest level of theory, the CASSCF-SOCI method with the triple zeta plus triple polarization augmented with two sets of higher angular momentum functions and two sets of diffuse functions basis set [TZ3P(2f,2d)+2diff], the energy separation (T0) between the ground (X˜ 1A1) and first excited (a˜ 3B1) states is determined to be 20.5 kcal/mol (0.890eV,7180cm−1), which is in excellent agreement with the experimental T0 value of 21.0 kcal/mol (0.910eV,7340cm−1). With the same method the T0 value for the a˜ 1B1−X˜ 1A1 separation is predicted to be 45.1 kcal/mol (1.957 eV,15780 cm−1), which is also in fine agreement with the experimental value of 44.4 kcal/mol (1.925 eV,15530 cm−1). The T0 value for the B˜ 1A1−X˜ 1A1 separation is determined to be 79.6 kcal/mol (3.452 eV,27 840 cm−1). After comparison of theoretical and experimental T0 values for the a˜ 3B1 and a˜ 1B1 states and previous studies, error bars for the B˜ 1A1 state are estimated to be ±1.5 kcal/mol (±525 cm−1). The predicted geometry of the B˜ 1A1 state is re(SiH)=1.458 and θe=162.3∘. The physical properties including harmonic vibrational frequencies of the B˜ 1A1 state are newly determined.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002140050270

Permalink