Speaker
Description
Buckminsterfullerene C₆₀ is a benchmark large molecule — highly symmetric, rigid, and readily sublimed and ionized — making its cation C₆₀⁺ one of the most accessible large molecular ions to produce. It is also the first identified molecular carrier of the diffuse interstellar bands, assigned through cold gas-phase spectroscopy, so buffer-gas cooling of C₆₀⁺ in RF traps directly underpins such measurements. Yet for large ions the relevant collision dynamics — transient complex formation in deep ion–atom wells and RF-driven collisional heating — remain poorly characterized. We present classical molecular-dynamics simulations of a single trapped C₆₀⁺ ion (720 amu; Ω/2π = 0.75 MHz) buffer-gas cooled by helium or cadmium, using ab initio ion–atom potential-energy surfaces (well depths D_e ≈ 102 K for He, 3971 K for Cd) and a moving-bubble buffer-atom injection scheme. Over trajectory ensembles we track the single-ion temperature (including micromotion), cooling curves, and complex-formation statistics. Contrasting a light, warm gas (He, 4 K) with a heavy, ultracold one (Cd, 6.4 mK), the ion cools toward the bath on ms–s timescales, its steady-state temperature set by competition between collisional cooling and RF micromotion heating — enhanced during long-lived captures in the deep Cd well [He ~6.8 K; Cd ~12 mK]. These stiff capture dynamics are resolved with a well-period-adaptive symplectic integrator benchmarked against embedded Runge–Kutta. We discuss prospects for cooling large molecular ions toward the mK regime.