DESTINY: A new binding-energy-resolved astrochemical model. Self-Consistent Competitiveness using Branched Absorbing Markov Chains

Under cryogenic interstellar conditions, the amorphous structure of interstellar ice results in binding-energy distributions (BEDs) per species. However, only few studies attempted their inclusion in astrochemical models. This paper introduces DESTINY, a deterministic astrochemical framework designed to incorporate BEDs while self-consistently accounting for the competition among activated surface processes. The framework is currently constrained to a monolayer. Surface processes initiated by surface species were reformulated using a trial-frequency-capped formalism represented through branched absorbing Markov chains. The ordinary differential equations system is redefined based on normalized effective probabilities. Preliminary results based on a reduced surface network are discussed. To isolate the effects of the probabilistic reformulation from those of BED discretizations, DESTINY is benchmarked against Nautilus, a single-BE rate-equation based open source code. In the single-BE limit, DESTINY reproduces the behavior of Nautilus for most species. The largest deviations are obtained for CH_ x∈ 2,4 ; these are traced to a different treatment of the H_2 encounter effect, impacting both H_2 surface exploration and desorption efficiencies within the DESTINY framework. Introducing BEDs redistributes species among adsorption sites of different depths, altering the balance between diffusion, desorption, and reactions. Significant effects are found for H, H_2, NH_x, NO, CH_x, CO, and H_xCO. Preliminary results showed that the self-consistent treatment of the H_2 encounter effect coupled with the explicit treatment of BEDs can substantially modify grain-surface chemistry. Further framework extensions are expected in the near future.