Donald D. Shillady

Ab initio equilibrium constants for H2O–H2O and H2O–CO2

Ab initio 6‐31G** electronic structure calculations have been used to determine the minimum energy geometries and vibrational frequencies of molecular clusters of water and carbon dioxide. Application of statistical thermodynamics leads to theoretical equilibrium constants for gas phase dimerization of water and the formation of an adduct of carbon dioxide with water. The low energy vibrations of the clusters lead to much larger contributions to the vibrational partitioning of the energy than do the fundamental vibrations of the monomeric species. A new ‘‘Harmonic‐Morse’’ formula is derived to estimate anharmonicity from optimized harmonic frequencies and two additional values on the potential surface for each vibration. These ab initio calculations of equilibrium constants are very close to recent measurements and fall within the range of values obtained by other methods. This no‐parameter treatment gives excellent agreement for the equilibrium of H2O–CO2 near the supercritical fluid range of CO2 and suggests that a ‘‘Theory of Significant Clusters’’ may be extended to a model of supercritical fluids which includes the effects of anharmonicity.

A new iso-chemical model of the hydrogen molecule

Abstract Despite outstanding advances throughout this century, we still lack final knowledge on the structure of the hydrogen molecule because of a number of insufficiencies in available models identified in the text. In this paper we use the recently achieved covering of quantum chemistry called hadronic chemistry in its iso-chemical branch, and introduce a new model of the hydrogen molecule characterized by a bond at short distances of the two valence electrons into a singlet quasi-particle state called iso-electronium. We study the iso-chemical model of the hydrogen molecule with a stable iso-electronium describing an oo-shaped orbit around the respective two nuclei, and another model with a weaker realization of the iso-electronium as a partially stable state. We show that the new model provides, apparently for the first time, an exact representation of the binding energy and other characteristics of the hydrogen molecules from axiomatic principles, without ad hoc modifications of theory. In subsequent papers we shall show that the new model permits apparently novel advances in the energy, liquefaction and other technological applications of the hydrogen.

Sturmian basis matrix solution of vibrational potentials

Abstract An efficient basis set for use with the Harris, Engerholm and Gwinn solution of one-dimensional vibrational potentials has been derived from centrosymmetric sturmian Laguerre functions using the l = 0 condition. Six-figure accuracy is achieved for n bound levels of the Morse and Fues potentials using 4 n sturmian functions. With simple formulas and sparse arrays, convergence to all bound levels is achieved.

A new isochemical model of the water molecule

Abstract Despite outstanding advances throughout this century, we still lack final knowledge on the structure of the water molecule because of a number of insufficiencies in available models identified in the text. In a preceding paper we submitted a covering of quantum chemistry called hadronic chemistry in its isochemical branch, and introduce a new model of the hydrogen molecule characterized by a bond at short distances of the two valence electrons into a singlet quasi-particle state called isoelectronium. In this paper we introduce, apparently for the first time, the isochemical model of the water molecule which is characterized by two isoelectronia, one per each H–O dimer and show that the model: (1) introduces a new strong force responsible for the molecular bond; (2) explains the reason why the water molecule has only two hydrogen atoms; (3) provides an accurate representation of the binding energy from the first axiomatic principles without ad hoc modifications; (4) permits a correct representation of electric and magnetic moments; and (5) reduces by at least a factor of 1000 computer usages for calculations due to a much faster convergent series. Experimental verifications, applications and novel predictions of the model are studied in subsequent papers.

Conformational complexity of melatonin in water and methanol.

The magnetic circular dichroism (MCD) spectra of melatonin in water and methanol solutions is compared to the MCD spectra of indole and five melatonin conformations observed in low temperature jet spectroscopy. Based on a survey of indole compounds using Slater type orbitals-6G(d,p) and B3LYP/6-31G(d) energies, and CNDO/S-D calculations of MCD spectral bands, a dominant structure with a water molecule bridging the amide-keto oxygen and indole Nz-H atoms is proposed as the best fit for the MCD of aqueous melatonin. In methanol an additional band appears at 310 nm which is supported only by solvated structures in which the alkyl-amide arm is extended away from the indole moiety.

Improved convergence modification of the orthogonal gradient multiconfiguration SCF method

Abstract The orthogonal gradient multiconfigurational method of Golebiewski, Hinze and Yurtsever has been modified to produce more rapidly a symmetric form of the generalized Fock ( F ) matrix. Test calculations using MINDO/3 and GAUS70 integrals show F ′ = 1.25 F −0.25 F + to be more rapidly convergent than F alone when used with the orthogonal gradient transformation.

Semiempirical description of the C6H5N reactive intermediate in phenyl azide photolysis

The C6H5N intermediate generated by photolysis of phenyl azide in solution is studied by semiempirical computations separately parametrized for thermochemistry and spectra. We find that the intermediate which absorbs only weakly in the region 320–370 nm and which is trapped by amines is the bicyclic azirine singlet, as proposed by DeGraff, Gillespie and Sundberg. Other species such as azepinylidine, the distorted azallyl azacycloheptatetraene and pyridyl carbene seem less likely candidates, either because they would be expected to have a rich spectrum in the visible or because they are unstable relative to the azirine. The adduct formed during trapping by amines rearranges by a suprafacial [1, 3] sigmatropic shift, in contradiction to Woodward-Hoffman predictions. Details of the path are easily rationalized as due to specific orbital interactions.

A slater-transform-preuss (STP) wavefunction for the ground state of Be

Abstract A class of integral transform functions previously applied to He and Li has been extended to the ground state of Be where an energy of −14.567553 au was obtained. Although the function is slightly less than double-zeta quality and requires numerical integration techniques, it is shown how the parameters of the function can be related to single-zeta screening constants while obtaining much improved minimal basis energies.

An experimental and theoretical study of the gas-phase decomposition of monoprotonated peptide nucleic acids

Peptide nucleic acids (PNAs) are DNA/RNA mimics which have recently generated considerable interest due to their potential use as antisense and antigene therapeutics and as diagnostic and molecular biology tools. These synthetic biomolecules were designed with improved properties over corresponding oligonucleotides such as greater binding affinity to complementary nucleic acids, enhanced cellular uptake, and greater stability in biological systems. Because of the stability and unique structure of PNAs, traditional sequence confirmation methods are not effective. Alternatively, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry shows great potential as a tool for the characterization and structural elucidation of these oligonucleotide analogs. Extensive gasphase fragmentation studies of a mixed nucleobase 4-mer (AACT) and a mixed nucleobase 4-mer with an acetylated N-terminus (N-acetylated AACT) have been performed. Gas-phase collision-induced dissociation of PNAs resulted in water loss, cleavage of the methylene carbonyl linker containing a nucleobase, cleavage of the peptide bond, and the loss of nucleobases. These studies show that the fragmentation behavior of PNAs resembles that of both peptides and oligonucleotides. Molecular mechanics (MM+), semiempirical (AM1), and ab initio (STO-3G) calculations were used to investigate the site of protonation and determine potential low energy conformations. Computational methods were also employed to study prospective intramolecular interactions and provide insight into potential fragmentation mechanisms.

An improved CNDO/S study of the circular dichroism of 1-methylindan in the 275—170 nm region

Abstract The circular dichroism rotational strengths for 1-methylindan have been computed using deorthogonalized CNDO/S orbitals in the dipole velocity representation and including both sigma and pi singly-excited configuration for planar, axial-and equatorial-methyl conformations. The first seven bands in the wavelength range of 275 nm to 170 nm agree closely with the experimental gas phase spectrum of Allen and Schnepp and the signs of the rotational strengths indicate a nearly equal mixture of axial equatorial-conformations in that spectrum.