Ultraslow radiative cooling of C${}_n^{-}$ ($n=3-5$)

Abstract

Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, C${}_n^{-}$ ($n=3-5$), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of $\approx$10${}^{-14}$\,mbar and temperature of $\approx$13\,K, allowing storage of mass-selected ions for hours and providing conditions coined a "molecular cloud in a box". Here, we construct two-dimensional (2D) photodetachment spectra for the target anions by recording photodetachment signal as a function of irradiation wavelength and ion storage time (seconds to minute timescale). Ion cooling lifetimes, which are associated with infrared radiative emission, are extracted from the 2D photodetachment spectrum for each ion by tracking the disappearance of vibrational hot-band signal with ion storage time, giving $\frac{1}{e}$ cooling lifetimes of 3.1$\pm$0.1\,s (C${}_3^{-}$), 6.8$\pm$0.5\,s (C${}_4^{-}$) and 24$\pm$5\,s (C${}_5^{-}$). Fits of the photodetachment spectra for cold ions, i.e. those stored for at least 30\,s, provides adiabatic detachment energies in good agreement with values from laser photoelectron spectroscopy. Ion cooling lifetimes are simulated using a Simple Harmonic Cascade model, finding good agreement with experiment and providing a mode-by-mode understanding of the radiative cooling properties. The 2D photodetachment strategy and radiative cooling modeling developed in this study could be applied to investigate the ultraslow cooling dynamics of wide range of molecular anions.

References in corpus (11)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
• Astronomical identification of CN-, the smallest observed molecular anion
• Detection of C5N- and vibrationally excited C6H in IRC +10216
• First storage of ion beams in the Double Electrostatic Ion-Ring Experiment - DESIREE
• The Cryogenic Storage Ring CSR
• Rotationally cold OH${}^{-}$ ions in the cryogenic electrostatic ion-beam storage ring DESIREE
• Radiative rotational lifetimes and state-resolved relative detachment cross sections from photodetachment thermometry of molecular anions in a cryogenic storage ring
• Spontaneous decay of small copper cluster anions Cu${}_n^{-}$, $n=3-6$ on long time scales
• Radiative lifetimes of the bound excited states of ${\text{Pt}}^{-}$
• Decays of excited silver cluster anions Ag${}_n$, $n=4$ to $7$, in DESIREE

Cited by in corpus (1)

• Cascade infrared thermal photon emission