Chemical Reaction Network for AGB Star Envelopes

The reaction network is based on previous networks which were applied to astrochemical models of AGB star envelopes (Frenklach 1989, Cherchneff 2012), with updated and refined kinetic parameters where possible. The current network has been expanded to include modifications and additions related to PAH growth reactions. Network Structure The network contains the following columns: 1 - Reaction Type 1: Gas-phase reactions with rate constants calculated by: k(T) = A (T/300)n e-Ea/RT 17: Gas-phase reactions with rate constants calculated by: k(T) = A Tn e-Ea/RT 11: Accretion reactions 12: Desorption reactions 18: Eley-Rideal surface reactions 2,3,4 - Reagents Reagent #1, Reagent #2, Reagent #3 5,6,7,8 - Products Product #1, Product #2, Product #3, Product #4 9,10,11 - Parameters A (pre-exponential factor), n (temperature exponent), Ea (activation energy) 12 - Dual Arrhenius Flag "1" indicates the rate constant is calculated as the sum of two Arrhenius expressions 13 - Reverse Reaction Flag "0" indicates a reverse reaction is automatically added with rate calculated through equilibrium constant 14 - References Source literature for the reaction 15 - Comments Additional notes about the reaction Notation System A specialized notation system compatible with the BRAHMA computational framework was developed for the reaction network, adhering to the following conventions: Basic Molecules Small molecules and substituents (e.g., H2, H2O, CO, C2H2) retain standard chemical formulas as identifiers. Aromatic Compounds Aromatic moieties are denoted with the prefix a-: Benzene: a-C6H6 Pyrene: a-C16H10 Substituents on aromatic rings are appended after the core structure (e.g., toluene: a-C6H5CH3). For multiple substituents, brackets or additional symbols may be used. Radical Notation The asterisk (*) distinguishes isomeric radicals based on the position of the unpaired electron: C4*H3: Unpaired electron on an internal carbon. C4H3*: Unpaired electron on a terminal carbon. Compounds labeled as CxHiS in Frenklach's works are represented here as Cx*Hi, while CxHiU compounds become CxHi*. If only one radical isomer is used, the position of the unpaired electron may be omitted. Isomer Labeling Structurally distinct isomers may include additional textual labels after a ! symbol for clarity: Anthracene: a-C14H10!anth Phenanthrene: a-C14H10!phen