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Articles 361 - 384 of 384
Full-Text Articles in Chemistry
Theoretical Vibrational Study Of The Fx⋅⋅⋅O(Ch3)2 Hydrogen‐Bonded Complex, Y. Bouteiller, C. Mijoule, M. M. Szczesniak, Steve Scheiner
Theoretical Vibrational Study Of The Fx⋅⋅⋅O(Ch3)2 Hydrogen‐Bonded Complex, Y. Bouteiller, C. Mijoule, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental vFX (X=H,D) in the FX⋅⋅⋅O(CH3)2 hydrogen‐bonded system. The two‐dimensional potential energy surface V(rFH,RF⋅⋅⋅O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the …
Vibrational Frequencies And Intensities Of H‐Bonded And Li‐Bonded Complexes. H3n⋅⋅Hcl And H3n⋅⋅Licl, M. M. Szczesniak, I. J. Kurnig, Steve Scheiner
Vibrational Frequencies And Intensities Of H‐Bonded And Li‐Bonded Complexes. H3n⋅⋅Hcl And H3n⋅⋅Licl, M. M. Szczesniak, I. J. Kurnig, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The geometries, energetics, and vibrational spectra are calculated for the two complexes at the SCF and correlated MP2 levels using the 6‐31G∗∗ basis set, augmented by a second set of d functions on Cl. While correlation represents an important factor in the binding of H3 N⋅⋅HCl, it contributes little to the stronger Li bond. Unlike the HCl stretch νs which decreases substantially in frequency and is greatly intensified in H3 N⋅⋅HCl, the frequency of the LiCl stretch undergoes an increase and little change is noted in its intensity, conforming to prior spectral measurements. The intensities of the …
Structure, Energetics, And Vibrational Spectrum Of H2o–Hcl, Z. Latajka, Steve Scheiner
Structure, Energetics, And Vibrational Spectrum Of H2o–Hcl, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
H2O–HCl is studied using a number of basis sets including 6‐31G∗∗ and variants which are augmented by a diffuse sp shell and a second set of d functions on O and Cl. Optimization of the geometry of the complex is carried out including explicitly electron correlation and counterpoise correction of the basis set superposition error (BSSE) at both the SCF and correlated levels. Correlation strengthens and shortens the H bond while BSSE correction leads to an opposite trend; these two effects are of different magnitude and hence cancel one another only partially. ΔH°(298 K) is …
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hfvibrational Frequencies And Intensities Of H‐Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hfvibrational Frequencies And Intensities Of H‐Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H3X–HF and 1:2 H3X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH3 stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH3 which exhibits little sensitivity in this regard). …
Primary And Secondary Basis Set Superposition Error At The Scf And Mp2 Levels. H3n‐‐Li+ And H2o‐‐Li+, Z. Latajka, Steve Scheiner
Primary And Secondary Basis Set Superposition Error At The Scf And Mp2 Levels. H3n‐‐Li+ And H2o‐‐Li+, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The primary basis set superposition error (BSSE) results from the artificial lowering of the energy of each subunit of a pair by the presence of ‘‘ghost orbitals’’ of its partner. In addition, these ghost orbitals perturb the one‐electron properties of the molecule, causing a change in the interaction energy, an effect known as secondary BSSE which is not corrected by the counterpoise procedure. The primary and secondary BSSE are calculated for the interactions of NH3 and H2O with Li+, using a variety of different basis sets. It is found that the 2° BSSE can be …
The Potential Energy Surface Of (Nh3)2, Z. Latajka, Steve Scheiner
The Potential Energy Surface Of (Nh3)2, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations at the SCF and correlated levels are carried out to characterize the potential energy surface of the NH3 dimer. The two basis sets used are 4‐31G∗ and a larger one containing two sets of d‐functions on N centers, 6‐31G∗∗ (1p, 2d). The only minimum occurring on the surface is a cyclic C2h structure in which the two H‐bonding protons are displaced 42° from the N‐‐N axis. The surface contains a very shallow valley along the direction leading from this geometry to a single linear H bond although …
Correction Of The Basis Set Superposition Error In Scf And Mp2 Interaction Energies. The Water Dimer, M. M. Szczesniak, Steve Scheiner
Correction Of The Basis Set Superposition Error In Scf And Mp2 Interaction Energies. The Water Dimer, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
There has been some discussion concerning whether basis set superposition error is more correctly evaluated using the full set of ghost orbitals of the partner molecule or some subset thereof. A formal treatment is presented, arguing that the full set is required at the Møller–Plesset level. Numerical support for this position is provided by calculation of the interaction energy between a pair of water molecules, using a series of moderate sized basis sets ranging from 6‐31G∗∗ to the [432/21] contraction suggested by Clementi and Habitz. These energies, at both the SCF and MP2 levels, behave erratically with respect to changes …
Comparison Of Proton Transfers In (S2h5)+ And (O2h5)+, L. Bigham, Steve Scheiner
Comparison Of Proton Transfers In (S2h5)+ And (O2h5)+, L. Bigham, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The energetics and electronic rearrangements associated with proton transfer between S atoms in (H2S–H–SH2)+ are calculated using ab initio molecular orbital methods and compared with similar data in the first‐row analog (H2O–H–OH2)+. The full potential energy surface of (S2H5)+, calculated as a function of the H‐bond length as well as the position of the proton, contains two equivalent minima separated by a small energy barrier, whereas the surface of (O2H5)+ contains a single minimum corresponding to a symmetric …
Contribution Of Dispersion To The Properties Of H2s‐‐Hf And H2s‐‐Hcl, M. M. Szczesniak, Steve Scheiner
Contribution Of Dispersion To The Properties Of H2s‐‐Hf And H2s‐‐Hcl, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out using a doubly polarized basis set. Dispersion, evaluated by second‐order Møller–Plesset perturbation theory (MP2), is found to have a profound influence on the stabilities and structures of the H‐bonded complexes. The contribution of dispersion to the H‐bond energies of H2S‐‐HF and H2S‐‐HCl is 44% and 69%, respectively, placing this attractive term second in magnitude only to electrostatics. Reductions of the intermolecular distance of 0.17 and 0.34 Å result from inclusion of correlation effects. Nevertheless, the influence of dispersion upon the angular characteristics of the …
Influence Of Basis Set On The Calculated Properties Of (H3n–Hcl), Z. Latajka, Steve Scheiner
Influence Of Basis Set On The Calculated Properties Of (H3n–Hcl), Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The structure of (H3N–HCl) is investigated by ab initio calculations using a number of different basis sets ranging from minimal to split valence. The effects of including a diffuse sp shell and d orbitals on Cl are considered as well. The geometries of the complex and the isolated subunits are fully optimized. Minimal basis sets (STO‐3G, STO‐6G, and MINI‐1) lead to an overestimate of the interaction between the subunits. Addition of d functions produces only a marginal improvement. The 3‐21G, 3‐21+G, MIDI‐1, and LP‐31G split‐valence sets erroneously predict an ion pair …
Effects Of Basis Set And Electron Correlation On The Calculated Properties Of The Ammonia Dimer, Z. Latajka, Steve Scheiner
Effects Of Basis Set And Electron Correlation On The Calculated Properties Of The Ammonia Dimer, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out for (NH3)2 with a 6‐31G∗∗(1p,2d) basis set containing diffuse polarization functions. Electron correlation is included via second‐order Møller–Plesset perturbation theory (MP2). At the SCF level, the equilibrium R(NN) distance is 3.54 Å and the interaction energy is −2.35 kcal/mol. Inclusion of correlation enhances the attraction substantially, increasing the energy to −4.05 kcal/mol and reducing the intermolecular separation by 0.20 Å. Comparison with previous results at the SCF level demonstrates a variety of errors including exaggerated dipole moments, underestimation of polarization …
Ab Initio Comparison Of H Bonds And Li Bonds. Complexes Of Lif, Licl, Hf, And Hcl With Nh3, Z. Latajka, Steve Scheiner
Ab Initio Comparison Of H Bonds And Li Bonds. Complexes Of Lif, Licl, Hf, And Hcl With Nh3, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out on the complexes H3N–LiF, H3N–LiCl and their analogs H3N–HF and H3N–HCl as well as the isolated subunits. Double‐zeta basis sets, augmented by two sets of polarization functions, are used in conjunction with second‐order Moller–Plesset perturbation theory (MP2) for evaluation of electron correlation effects. The Li bonds are found to be substantially stronger than their H‐bonding counterparts, due in large measure to the greater dipole moments of the LiX subunits. Correlation has a large effect on the geometry and energetics of …
Studies Of Dispersion Energy In Hydrogen‐Bonded Systems. H2o–Hoh, H2o–Hf, H3n–Hf, Hf–Hf, M. M. Szczesniak, Steve Scheiner
Studies Of Dispersion Energy In Hydrogen‐Bonded Systems. H2o–Hoh, H2o–Hf, H3n–Hf, Hf–Hf, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Dispersion energy is calculated in the systems H2O–HOH, H2O–HF, H3N–HF, and HF–HF as a function of the intermolecular separation using a variety of methods. M≂ller–Plesset perturbation theory to second and third orders is applied in conjunction with polarized basis sets of 6‐311G∗∗ type and with an extended basis set including a second set of polarization functions (DZ+2P). These results are compared to a multipole expansion of the dispersion energy, based on the Unsöld approximation, carried out to the inverse tenth power of the intermolecular distance. Pairwise evaluation is also carried out using both atom–atom …
Proton Transfers Between First‐ And Second‐Row Atoms: (H2ohsh2)+ And (H3nhsh2)+, Steve Scheiner
Proton Transfers Between First‐ And Second‐Row Atoms: (H2ohsh2)+ And (H3nhsh2)+, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio molecular orbital methods are used to study the transfer of the central proton along the hydrogen bonds in (H2OHSH2)+ and (H3NHSH2)+. Proton transfer potentials are generated using the 4‐31G∗ basis set at the Hartree–Fock level for various values for the hydrogen bond length R(XS). Full geometry optimizations are carried out at each stage of proton transfer. The barrier to proton transfer increases as the hydrogen bond is lengthened. For a given bond length, the highest barriers are observed for transfer from …
Ab Initio Study Of Fh–Ph3 And Clh–Ph3 Including The Effects Of Electron Correlation, Z. Latajka, Steve Scheiner
Ab Initio Study Of Fh–Ph3 And Clh–Ph3 Including The Effects Of Electron Correlation, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out for FH–PH3 and ClH–PH3 using a basis set including two sets of polarization functions. Electron correlation is incorporated via Møller–Plesset perturbation theory to second and (in part) to third orders. The basis set is tested and found to produce satisfactory treatments of subsystem properties including geometries and dipole moments as well as the proton affinity and inversion barrier of PH3. Electron correlation is observed to markedly enhance the interaction between PH3 and the hydrogen halides. Its contribution to the complexation energy is 30% …
Theoretical Study Of H2o–Hf And H2o–Hcl: Comparison With Experiment, M. M. Szczesniak, Steve Scheiner, Y. Bouteiller
Theoretical Study Of H2o–Hf And H2o–Hcl: Comparison With Experiment, M. M. Szczesniak, Steve Scheiner, Y. Bouteiller
Chemistry and Biochemistry Faculty Publications
The H bonds in H2O–HF and H2O–HCl are studied and compared using ab initio molecular orbital methods and the results compared to experimental data. Basis sets used are: (i) triple valence 6‐311G∗∗ and (ii) double ζ with two sets of polarization functions. Electron correlation, included via second‐ and third‐order Møller–Plesset perturbation theory, is found to have profound effects on both systems, particularly H2O–HCl. Both H bonds are strengthened substantially with a concomitant reduction in length. H‐bond energies and geometries calculated at correlated levels are in excellent accord with …
Role Of D Functions In Ab Initio Calculation Of The Equilibrium Structure Of H2s–Hf, Steve Scheiner
Role Of D Functions In Ab Initio Calculation Of The Equilibrium Structure Of H2s–Hf, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Full geometry optimizations are performed to determine the equilibrium geometry of the hydrogen‐bonded complex H2S–HF. The angle between the plane of the H2S moiety and the H‐bond axis calculated with the 4–31 G basis set is 106° as compared to the experimental value of 91±5°. This quantity is reduced significantly when d orbitals are added to the basis set, yielding an angle within experimental error of 91°. (AIP)
Møller-Plesset Treatment Of Electron Correlation In (Hohoh)-, M. M. Szczesniak, Steve Scheiner
Møller-Plesset Treatment Of Electron Correlation In (Hohoh)-, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The effects of electron correlation on the calculated properties of the (HOHOH)− anion are studied using Møller–Plesset (MP) perturbation theory. With this technique, inclusion of corrections up to third order are shown to provide results quite similar to those obtained with an extensive CI approach when equivalent basis sets are used. Barriers to proton transfer between the two oxygen atoms at a fixed R(OO) distance are computed with a number of basis sets ranging from split‐valence 4–31G to triple‐valence with polarization functions on all atoms, 6–311G∗∗. Each successive enlargement of the basis set leads to a greater barrier. …
Comparison Of Proton Transfers In Cationic Heterodimers And Homodimers Of Nh3 And Oh2, Steve Scheiner
Comparison Of Proton Transfers In Cationic Heterodimers And Homodimers Of Nh3 And Oh2, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio molecular orbital methods are used to study proton transfers in the cationic heterodimer (H3NHOH2)+ as well as the symmetric homodimers (H2OHOH2)+ and (H3NHNH3)+. All calculations are carried out at the Hartree–Fock level with a 4‐31G basis set to ensure consistency. For proton transfers along a linear hydrogen bond in the heterodimer, asymmetric single‐well potentials with a minimum corresponding to (NH4)+(OH2) are obtained for R(NO) distances of less than 2.85 …
Proton Transfers In Hydrogen‐Bonded Systems. Vi. Electronic Redistributions In (N2h7)+ And (O2h5)+, Steve Scheiner
Proton Transfers In Hydrogen‐Bonded Systems. Vi. Electronic Redistributions In (N2h7)+ And (O2h5)+, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Electronic rearrangements accompanying transfer of the central proton between the two XHn units of (H3NHNH3)+ and (H2OHOH2)+ are studied using ab initio molecular orbital methods. Electron density difference maps are calculated by subtracting the density of the equilibrium structure (X–H‐‐‐X) from that of the midpoint geometry (X‐‐H‐‐X) using the split‐valence 4‐31G basis set. Some of the features revealed by the maps are common to both systems while others indicate significant differences between nitrogen and oxygen. Decomposition of the total electron density into …
Studies Of The Reorientational Relaxation Of Pyridine In Water By Depolarized Rayleigh Light Scattering, C. H. Wang, Scott L. Whittenburg, P. A. Lund, D. H. Christensen
Studies Of The Reorientational Relaxation Of Pyridine In Water By Depolarized Rayleigh Light Scattering, C. H. Wang, Scott L. Whittenburg, P. A. Lund, D. H. Christensen
Chemistry and Biochemistry Faculty Publications
The depolarized Rayleigh spectra of aqueous solutions of pyridine have been studied using a high‐finesse Fabry–Perot interferometer as a function of temperature and concentration. The Rayleigh relaxation times are found to have a complex concentration and viscosity dependence. The classical Stokes–Einstein–Debye equation for molecular reorientation breaks down in this system. The Rayleigh relaxation time of pyridine molecules is not determined by the macroscopic shear viscosity of the solution. The specific interaction due to the formation of hydrogen bonds between pyridine and water molecules plays a very important role in affecting the relaxation time. At a fixed temperature the plot of …
Light Scattering Studies Of Transverse Sound Wave And Molecular Motion In Benzonitrile, Scott L. Whittenburg, C. H. Wang
Light Scattering Studies Of Transverse Sound Wave And Molecular Motion In Benzonitrile, Scott L. Whittenburg, C. H. Wang
Chemistry and Biochemistry Faculty Publications
The zero‐frequency shear wave dip appearing in the depolarized Rayleigh spectrum in benzonitrile has been studied as a function of concentration and temperature. The solution study was carried out at constant viscosity equal to the viscosity of liquid benzonitrile at each temperature. The result indicates that the presence of shear wave fine structure does not depend on the collective orientational fluctuations. The orientational and vibrational relaxation times of benzonitrile were measured at various concentrations and temperatures. The orientational relaxation times show no concentration dependence at any temperature, suggesting that the pair correlation is negligible at all concentrations. The orientational relaxation …
Light Scattering Studies Of Rotational And Vibrational Relaxations Of Acetonitrile In Carbon Tetrachloride, Scott L. Whittenburg, C. H. Wang
Light Scattering Studies Of Rotational And Vibrational Relaxations Of Acetonitrile In Carbon Tetrachloride, Scott L. Whittenburg, C. H. Wang
Chemistry and Biochemistry Faculty Publications
The rotational and vibrational relaxation times of acetonitrile–carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering. Using a Fabry‐Perot interferometer and single frequency laser source, we have shown that reliable results for the single particle orientational correlation times (τs) for CH3CN can be obtained by carrying out a concentration dependent depolarized Rayleigh scattering study. Raman scattering was shown to yield inconsistent results for τs in CH3CN. At constant viscosity, it was found that the Rayleigh scatteringrelaxation time (τRay) of CH3 …
A Comparison Of The Rough Sphere Rotational Diffusion Model With Experimental Results For Liquid Methyl Iodide, Dane R. Jones, Scott L. Whittenburg, C. H. Wang
A Comparison Of The Rough Sphere Rotational Diffusion Model With Experimental Results For Liquid Methyl Iodide, Dane R. Jones, Scott L. Whittenburg, C. H. Wang
Chemistry and Biochemistry Faculty Publications
No abstract available.