Radiative cooling of carbon cluster anions C2n+1− (n = 3–5)★
Department of Physics, Stockholm University, Stockholm, Sweden
2 School of Chemistry, University of East Anglia, Norwich, UK
3 School of Chemistry, University of Melbourne, Melbourne, Australia
4 Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédérale de Lausanne, EPFL SB ISIC LCPM, Station 6, CH-1015 Lausanne, Switzerland
5 Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
6 Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Petrópolis, Brazil
a e-mail: Mark.Stockett@fysik.su.se
Received in final form: 25 May 2020
Published online: 7 July 2020
Radiative cooling of carbon cluster anions C2n+1− (n = 3–5) is investigated using the cryogenic electrostatic ion storage ring DESIREE. Two different strategies are applied to infer infrared emission on slow (milliseconds to seconds) and ultraslow (seconds to minutes) timescales. Initial cooling of the ions over the millisecond timescale is probed indirectly by monitoring the decay in the yield of spontaneous neutralization by thermionic emission. The observed cooling rates are consistent with a statistical model of thermionic electron emission in competition with infrared photon emission due to vibrational de-excitation. Slower cooling over the seconds to minutes timescale associated with infrared emission from low-frequency vibrational modes is probed using time-dependent action spectroscopy. For C9− and C11−, cooling is evidenced by the time-evolution of the yield of photo-induced neutralization following resonant excitation of electronic transitions near the detachment threshold. The cross-section for resonant photo-excitation is at least two orders of magnitude greater than for direct photodetachment. In contrast, C7− lacks electronic transitions near the detachment threshold.
© The Author(s) 2020. This article is published with open access at Springerlink.com
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open access funding provided by Stockholm University.