Indene (C9H8) is the only polycyclic pure hydrocarbon identified in the interstellar medium to date, with an observed abundance orders of magnitude higher than predicted by astrochemical models. The dissociation and radiative stabilization of vibrationally hot indene cations are investigated by measuring the time-dependent neutral particle emission rate from ions in a cryogenic ion-beam storage ring for up to 100 ms. Time-resolved measurements of the kinetic energy released upon hydrogen atom loss from C 9 H 8 + , analyzed in view of a model of tunneling through a potential energy barrier, provide the dissociation rate coefficient. Master equation simulations of the dissociation in competition with vibrational and electronic radiative cooling reproduce the measured dissociation rate. We find that radiative stabilization arrests one of the main C9H8 destruction channels included in astrochemical models, helping to rationalize its high observed abundance.

An electrospray ion source has been coupled to a cryogenic electrostatic ion-beam storage ring to enable experimental studies of the fundamental properties of biomolecular ions and their reactions in the gas phase on longer timescales than with previous instruments. Using this equipment, we have measured the vibrational radiative cooling rate of the deprotonated anion of the chromophore of the cyan fluorescent protein, a color-shifted mutant of the iconic green fluorescent protein. Time-resolved dissociation rates of collisionally activated ions are first measured to benchmark a model of the dissociation rate coefficient. Storage time-dependent laser-induced dissociation rates are then measured to probe the evolution of the internal energy distribution of the stored ion ensemble. We find that significant heating of the electrosprayed ions occurs upon their extraction from the ion source, and that the radiative cooling rate is consistent with the prediction of a simple harmonic cascade model of vibrational relaxation.

Several small polycyclic aromatic hydrocarbons (PAHs) with closed-shell electronic structure have been identified in the cold, dark environment Taurus Molecular Cloud 1. We measure efficient radiative cooling through the combination of recurrent fluorescence (RF) and IR emission in the closed-shell indenyl cation (C9H7+), finding good agreement with a master equation model including molecular dynamics trajectories to describe internal-energy-dependent properties for RF. We find that C9H7+ formed with up to Ec=5.85 eV vibrational energy, which is ≈2 eV above the dissociation threshold, radiatively cool rather than dissociate. The efficient radiative stabilization dynamics are likely common to other closed-shell PAHs present in space, contributing to their abundance.