ADF-Clump Chemistry in Planetary Nebulae: Preliminary RATE22 Network Analysis (Steps 1–15)

This paper presents a comprehensive computational study of ion-molecule chemistry under conditions representative of the metal-rich, cold clumps invoked to explain the abundance discrepancy factor (ADF) in planetary nebulae. The full RATE22 gas-phase network (8258 reactions, 737 species) is integrated using a BDF solver with an analytic sparse Jacobian. Baseline calculations (Steps 1–6) cover the cosmic-ray ionization rate ζ = 10⁻¹⁷–10⁻¹⁴ s⁻¹, temperature T = 10–1000 K, metallicity Z = 1–30 × solar, and gas density n_H = 2×10³–10⁶ cm⁻³. Steps 7–10 extend the baseline with grain freeze-out, ionization balance diagnostics, UV shielding effects, and a 500-realisation Monte Carlo rate uncertainty analysis. Step 11 compares model predictions against millimetre-wave observations of three ADF-elevated planetary nebulae. Steps 12–15 develop a 6-layer concentric clump model with radial gradients in temperature, density, and extinction, and project it onto the plane of the sky. Ionic tracers H₃⁺, HCO⁺, and N₂H⁺ remain buffered across all 148 baseline integrations. At T ≤ 200 K and Z ≥ 2 × solar, a water ion cycle driven by H₃O⁺ emerges: OH abundance increases by up to a factor of 21 while HCN decreases by up to a factor of 500 over the same ζ range. This is a preliminary study. Steps 11–15 (observational comparison and spatial modelling) are incomplete and should be treated as exploratory only.Prepared with AI assistance. Computational resources: Kaggle (Intel Xeon 2.0 GHz, 4 cores). Dataset: steelk4568/rate22-final. Steps 1–10 are complete; Steps 11–15 are preliminary