A forecast for theoretical chemistry

Application of quantum mechanics in theoretical chemistr

Theoretical studies in interstellar cloud chemistry

This final report represents the completion of the three tasks under the purchase order no. SCPDE5620,1,2F. Chemical composition of gravitationally contracting, but otherwise quiescent, interstellar clouds and of interstellar clouds traversed by high velocity shocks, were modeled in a comprehensive manner that represents a significant progress in modeling these objects. The evolutionary chemical modeling, done under this NASA contract, represents a notable advance over the 'classical' fixed condition equilibrium models because the evolutionary models consider not only the chemical processes but also the dynamical processes by which the dark interstellar clouds may have assumed their present state. The shock calculations, being reported here, are important because they extend the limited chemical composition derivable from dynamical calculations for the total density and temperature structures behind the shock front. In order to be tractable, the dynamical calculations must severely simplify the chemistry. The present shock calculations take the shock profiles from the dynamical calculations and derive chemical composition in a comprehensive manner. The results of the present modeling study are still to be analyzed with reference to astronomical observational data and other contemporary model predictions. As far as humanly possible, this analysis will be continued with CRE's (Creative Research Enterprises's) IR&D resources, until a sponsor is found

Supersymmetry and the Hartmann Potential of Theoretical Chemistry

The ring-shaped Hartmann potential $V = \eta \sigma^{2} \epsilon_{0} \left( \frac{2 a_{0}}{r} - \frac{\eta a_{0}^{2}}{r^{2} sin^{2} \theta} \right)$ was introduced in quantum chemistry to describe ring-shaped molecules like benzene. In this article, the supersymmetric features of the Hartmann potential are discussed. We first review the results of a previous paper in which we rederived the eigenvalues and radial eigenfunctions of the Hartmann potential using a formulation of one-dimensional supersymmetric quantum mechanics (SUSYQM) on the half-line $\left[ 0, \infty \right)$. A reformulation of SUSYQM in the full line $\left( -\infty, \infty \right)$ is subsequently developed. It is found that the second formulation makes a connection between states having the same quantum number $L$ but different values of $\eta \sigma^{2}$ and quantum number $N$. This is in contrast to the first formulation, which relates states with identical values of the quantum number $N$ and $\eta \sigma^{2}$ but different values of the quantum number $L$.Comment: 24 pages; uses LaTex; to be published at the Theoretica Chimica Acta; hard copy available from the author upon request (use address: [email protected]

Circumstellar chemistry

The study of the outer envelopes of cool evolved stars has become an active area of research. The physical properties of CS envelopes are presented. Observations of many wavelengths bands are relevant. A summary of observations and a discussion of theoretical considerations concerning the chemistry are summarized. Recent theoretical considerations show that the thermal equilibrium model is of limited use for understanding the chemistry of the outer CS envelopes. The theoretical modeling of the chemistry of CS envelopes provides a quantitive test of chemical concepts which have a broader interest than the envelopes themselves

Theoretical and Computational Chemistry

Computer-based and theoretical approaches to chemical problems can provide atomistic understanding of complex processes at the molecular level. Examples ranging from rates of ligand-binding reactions in proteins to structural and energetic investigations of diastereomers relevant to organo-catalysis are discussed in the following. They highlight the range of application of theoretical and computational methods to current questions in chemical research

Study of surfaces and interfaces using quantum chemistry techniques

There are a number of difficulties in elucidating the microscopic details of the electronic states at surfaces and interfaces. The first step should be to determine the structure at the surface or interface, but this is difficult experimentally even for the clean, ordered surface and extremely difficult for cases with impurity atoms (e.g., nonordered oxide layers). The theoretical study of such geometries and energy surfaces is the subject of quantum chemistry. We present a review of some of the theoretical techniques from quantum chemistry that are being applied to surfaces. The procedure consists of treating a finite piece of the surface or interface as a molecule. Ab initio calculations are then carried out on the molecule using the generalized valence bond (GVB) method (with additional configuration interaction), thereby incorporating the dominant many‐body effects. The reliability of these techniques is discussed by giving some examples from molecular chemistry and the surfaces of solids. The strengths and weaknesses of this approach are compared with more traditional band theory related methods and are illustrated with various examples

Statistical Theory of Unimolecular Reactions and Intramolecular Dynamics

In the present lecture we review experimental and theoretical developments in the field of intramolecular dynamics during the past sixty years. In a concluding section we consider possible implications for intramolecular laser selective chemistry

Chemistry in Dense Molecular Clouds: Theory and Observational Constraints

For the most part, gas phase models of the chemistry of dense molecular clouds predict the abundances of simple species rather well. However, for larger molecules and even for small systems rich in carbon these models often fail spectacularly. We present a brief review of the basic assumptions and results of large scale modeling of the chemistry in dense molecular clouds. Particular attention will be paid to the influence of the gas phase ratios of the major elements in molecular clouds, and the likely role grains play in maintaining these ratios as clouds evolve from initially diffuse objects to denser cores with associated stellar and planetary formation. Recent spectral line surveys at centimeter and millimeter wavelengths along with selected observations in the submillimeter have now produced an accurate "inventory" of the gas phase elemental budgets in different types of molecular clouds, though gaps in our knowledge clearly remain. The constraints these observations place on theoretical models of interstellar chemistry can be used to gain insights into why the models fail, and show also which neglected processes must be included in more complete analyses. Looking toward the future, truly protostellar regions are only now becoming available for both experimental and theoretical study, and some of the expected modifications of molecular cloud chemistry in these sources are therefore outlined