Radiative cooling of polyyne anions: C4H− and C6H−

Abstract

The time-dependent photodetachment action spectra of the linear hydrocarbon anions C4H- and C6H- are investigated using the cryogenic electrostatic ion storage ring DESIREE. Radiative cooling characteristics of the ions on the millisecond to second timescale are probed by monitoring changes in the spectra as the ions cool by spontaneous infrared (IR) emission. A simple harmonic cascade (SHC) model is used to model the cooling processes. The cooling rates, extracted using Non-negative Matrix Factorization (NMF), are fit with 1/e lifetimes of 19 {plus minus} 2 s and 3.0 {plus minus} 0.2 s for C4H- and C6H-, respectively. For C4H-, the adiabatic detachment energy is determined from the cold ions' photodetachment spectra to be 3.45 {plus minus} 0.02 eV. The photodetachment spectrum and the ultraslow radiative cooling dynamics interpreted in the present work provide important data for understanding the thermal cooling properties of linear hydrocarbon anions and for refining the formation and destruction processes of these anions in astrochemical models.

Experimental radiative cooling rates of a polycyclic aromatic hydrocarbon cation

“…24 DESIREE has also been used for vibrational energy dependent action spectroscopy of astrophyscially relevant ions including PAHs, 25,26 substituted PAHs thought to form in interstellar ices, 27,28 and carbon cluster anions. 29,30 The methods used here have largely been described previously. 6,16 Briefly, 1-CNN (Sigma-Aldrich, >96%) was sublimed from powder in a resistively heated oven coupled to an electron cyclotron resonance (ECR) ion source (Pantechnik Monogan) using helium as a support gas.…”

“…24 DESIREE has also been used for vibrational energy dependent action spectroscopy of astrophysically relevant ions including PAHs, 25,26 substituted PAHs thought to form in interstellar ices, 27,28 and carbon cluster anions. 29,30…”