Senior Staff Renewal Program
Involving Development of
Chemical Reaction Database, 15-9246
Principal Investigator
Walter F. Huebner
Inclusive Dates: 03/29/01 - 06/11/01
Background - Time-variable evaporation by solar heating of a still unknown mixture of ices in comet nuclei generates continually escaping gases in the coma of a comet. Solar ultraviolet radiation dissociates and ionizes the gases. They then undergo chemical reactions that change with heliocentric and cometocentric distances. A chemical reaction network linked to solar radiation and gas dynamics is needed to relate the observed species to the icy composition of the nucleus. The ices provide important clues about the origin of the solar system. The objective of the project was to acquire a broader chemical database for the observed species, their parents, and decay products.
Approach - All data were put into a uniform format in a database directly accessible by the user. Data are categorized according to reaction type.
Accomplishments - All data have been placed in a chemical reaction database. SwRI has expanded the list of elements from which molecules can be formed from 8 to 15. The reaction network now contains approximately 240 chemical species related to each other by rate coefficients for over 1,100 reactions. The database also contains species and reactions important for the chemistry of Mars, Jupiter, and Saturn. A start has been made to add references for the sources of the data and quality indicators to identify reliability of the data. Many rate coefficients have been updated with newer rate coefficients. Data are categorized according to reaction types.
- As a result of this project, SwRI has developed database management tools for automatic data selection and data sorting, including:
- A code for automatic selection of species and the related reactions
- A code that sorts reactants, reaction products, type of reactions, complexity of molecules, size of rate coefficients, reliability indicators, or one of several other parameters.
- SwRI has developed computational tools for ion-molecule and gas-kinetic (neutral-neutral) rate coefficients, including:
- A code to calculate polarizabilities based on the additivity property of molar refractions from atomic, group, and structural elements present in a molecule
- A code to calculate rate coefficients based on the average dipole orientation (ADO) method for a charge-induced dipole and a charge-dipole interaction
- A code to calculate rate coefficients based on the Su and Chesnavich theory of parameterized trajectory simulations
- Methods for a functional approximation for electron impact dissociation cross sections as a function of electron energy
- An analogous method for electron impact ionization and dissociative ionization
- A code to calculate proton impact charge exchange based on the Langevin rate coefficient
- A method for determining reaction rates for electron dissociative recombination
- A code to calculate rate coefficients for hard-sphere collisions
- A code to calculate rate coefficients for Lennard-Jones (6 -12) interactions
- A code to calculate reverse reactions
