HYDROGEN-ATOM BOND INCREMENTS FOR CALCULATION OF THERMODYNAMIC PROPERTIES OF HYDROCARBON RADICAL SPECIES

Hydrogen atom bond increments (HBI) are defined and a data base is der ived for accurately estimating Delta H-f298(o), S-298(o), and C-p(T) ( 300 less than or equal to T/K less than or equal to 1500) on generic c lasses of hydrocarbon (HC) radical species relevant to combustion and atmospheric chemistry, using these thermodynamic property increments. The HBI group technique is based on known thermodynamic properties of the parent molecule and calculated changes that occur upon formation o f a radical via loss of a H atom. The HBI approach incorporates (i) ev aluated literature bond energies, (ii) calculated entropy and heat cap acity increments resulting from loss and/or change in vibrational freq uencies including frequencies corresponding to inversion of the radica l center, (iii) increments from changes in barriers to internal rotati on, and (iv) spin degeneracy. Twenty five HBI groups corresponding to alkyl (primary, secondary, and tertiary), vinyl, allenic, allylic, ben zyl, acetylenic, and other conjugated hydrocarbon radicals are defined , and their group values are calculated. The HBI soups, when coupled w ith thermodynamic properties of the appropriate ''parent'' molecule, y ield accurate thermodynamic properties for the respective radicals.