Daniel Zeroka

Vibrational frequencies and structural determinations of 1,4-thioxane.

We present a detailed analysis of the structure and infrared spectra of 1,4-thioxane. The vibrational frequencies of the 1,4-thioxane molecule were analyzed using standard quantum chemical techniques. Frequencies were calculated at the MP2 and DFT levels of theory using the standard 6-31G* basis set. The structural transformation of the chemical agent bis (2-chloroethyl) sulfide (HD, mustard gas) and the related symmetry to a previously study compound(4) makes the symmetry of the 1,4-thioxane molecule an interesting candidate for study. The molecule exists normally in a Cs configuration similar to the chair form of cyclohexane. High-energy forms of 1,4-thioxane with C1 and C2 symmetry also exist.

A theoretical and experimental study of Sb4O6: vibrational analysis, infrared, and Raman spectra

The first ab initio theoretical study of tetraantimony hexoxide (Sb4O6) is reported. The normal mode frequencies, intensities, and the corresponding vibrational assignments of Sb4O6 in T(d) symmetry were calculated using the GAUSSIAN 98 set of quantum chemistry codes at the Hartree-Fock (HF)/CEP-121G, Møller-Plesset (MP2)/CEP-121G, and density functional theory (DFT)/B3LYP/CEP-121G levels of theory. By comparison to experimental data deduced by our laboratory and others, correction factors for the calculated vibrational frequencies were determined and compared. Normal modes were decomposed into three non-redundant motions (Sb-O-Sb stretch, Sb-O-Sb bend, and Sb-O-Sb wag). Percent relative errors found for the HF, DFT, and MP2 corrected frequencies when compared to experiment are 5.8, 6.1, and 5.7 cm(-1), respectively. Electron distributions for selected molecular orbitals are also considered.

Variation of diamagnetic properties of the hydrogen molecule with internuclear separation

The diamagnetic susceptibility χ and the magnetic shielding constant for the hydrogen molecule are investigated in the range of internuclear separations R = 1.0–12 a.u. using a previously reported technique and the reported wavefunction of Fraga and Ransil. The values at Re = 1.4 a.u. are χ = −3.8837 × 10−6 cgs units and σ = 27.095 ppm. For normal H2, the averages over nuclear motion, where zero‐point vibration and centrifugal distortion are taken into account, are 〈χ〉=‐3.9761× 10‐6 cgs units and 〈σ〉=26.760 ppm at 300 °K; these averages are approximately 2.38% and 1.24%, respectively, smaller than the equilibrium values. The variation of 〈χ〉 and 〈σ〉 over the temperature interval 20–300 °K is considered, on the basis that intermolecular force contributions are zero, and is found to be quite small. Furthermore, a useful table of some integrals that frequently arise in magnetic shielding studies is included as an Appendix.The diamagnetic susceptibility χ and the magnetic shielding constant for the hydrogen molecule are investigated in the range of internuclear separations R = 1.0–12 a.u. using a previously reported technique and the reported wavefunction of Fraga and Ransil. The values at Re = 1.4 a.u. are χ = −3.8837 × 10−6 cgs units and σ = 27.095 ppm. For normal H2, the averages over nuclear motion, where zero‐point vibration and centrifugal distortion are taken into account, are 〈χ〉=‐3.9761× 10‐6 cgs units and 〈σ〉=26.760 ppm at 300 °K; these averages are approximately 2.38% and 1.24%, respectively, smaller than the equilibrium values. The variation of 〈χ〉 and 〈σ〉 over the temperature interval 20–300 °K is considered, on the basis that intermolecular force contributions are zero, and is found to be quite small. Furthermore, a useful table of some integrals that frequently arise in magnetic shielding studies is included as an Appendix.

Helix–Coil Transition in Heterogeneous Chains. I. Protein Model

Helix–coil transition curves are calculated for heterogeneous chains with random and correlated sequences of residue types by an approximate method. The distinction is made between the a priori probability of a residue sequence, and an effective probability which must be used when the sequence is treated as if it were in open chemical equilibrium with a reservoir. It is assumed that the effective probability does not correlate residue types in different sections of unbroken helix or coil. The required cumulants of the effective probability can then be determined from those of the a priori probability. Agreement with recent exact calculations is tested and found to be especially good when the cumulant expansion of the effective probability is terminated with three cumulants. The method is applicable to models of DNA which include entropy of ring formation. In this approximation the partition function for the heterogeneous chain has the same form as for the homogeneous chain, but an effective energy paramet...

Note on the correlation of the K-shell electron binding energy chemical shifts with NMR chemical shifts

Abstract The correlation of K-shell electron binding energy chemical shifts, ΔEb(ν), with NMR chemical shifts, δν, is investigated for some halomethanes for ν = 13C and F.

A theoretical study of methylphosphine CH3PH2 and selected isotopomers: vibrational analysis and infrared spectra

Abstract The normal mode frequencies and the corresponding vibrational assignments of methylphosphine and selected deuterated methylphosphines are studied theoretically. The gaussian 98 quantum chemistry code was used at the HF, MP2 and DFT/B3LYP level of theory with the 6-311G∗∗ basis set. Comparison was made for the infrared spectra of methylphosphine and its deuterated isotopomers between our theoretically predicted values and the experimentally determined vibrational frequencies. Correction factors of the calculated frequencies compared to the experimental values are reported for methylphosphine and its deuterated isotopomers for predominant vibrational motions. The root mean square deviation is reported as a measure of the quality of the predicted frequencies compared to the experimental values.

Evaluation of one-electron integrals for arbitrary operators V(r) over Cartesian Gaussians: application to inverse-square distance and Yukuwa operators

A general procedure is presented for generating one‐electron integrals over any arbitrary potential operator that is a function of radial distance only. The procedure outlines that for a nucleus centered at point C integrals over Cartesian Gaussians can be written as linear combinations of 1‐D integrals. These Cartesian Gaussian functions are expressed in a compact form involving easily computed auxiliary functions. It is well known that integrals over the Coulomb operator can be expressed in terms of Fn(T) integrals, where \documentclass{article}\pagestyle{empty}\begin{document}

Adsorption of Methyl or Methoxy Species on Ni(110)

F_n \left(T \right) = \int_0^1 {u^{2n} e^{ - Tu^2 } {\rm d}u}