Emma K. Anderson's research while affiliated with Aarhus University and other places

Publications (6)

Article
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Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optical...
Article
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By repeatedly probing the a1Δ excited state and the X3Σ− ground-state populations in a beam of CH− ions stored in a cryogenic ion-beam storage ring for 100 s, we extract an intrinsic lifetime of 14.9±0.5 s for this excited state. This is far longer than all earlier experimental and theoretical results, exposing large difficulties in measuring and c...
Article
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Radiative cooling of carbon cluster anions C 2n+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 prob...
Conference Paper
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We store a 10 keV OH⁻ ion-beam at 13.5 ± 0.5 K in one of the DESIREE storage rings. Using photodetachment thermometry we measure the effective relative photodetachment cross section at different storage times and determine the rotational temperature of the ions to be 13.4 ± 0.2 K in agreement with the macroscopic temperature. A model cross section...
Article
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A recent study of soft X-ray absorption in native and hydrogenated coronene cations, C$_{24}$H$_{12+m}^+$ $m=0-7$, led to the conclusion that additional hydrogen atoms protect (interstellar) Polycyclic Aromatic Hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collision...
Article
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We have measured the spontaneous neutral particle emission from beams of copper cluster anions (Cu−N, N = 3 − 6) stored in an electrostatic storage ring. These experiments have show that multiple structural isomers may be present in the beam.

Citations

... This method would be particularly powerful for long-lived metastable states along with complementary studies such as the recent lifetime measurement of metastable CH − (>10 s) at DESIREE. 52) At RICE, we are currently working towards the photodetachment spectroscopy of C À 2 using a laser ablation source to see the difference between the initial temperatures. Experiments with extended storage times to more than several seconds are also in preparation. ...
... 11,12 Improvement of the vacuum (~10 !"# ) now makes it possible to store ions for hours and extends accordingly the time range of measurement of the decay of molecular anions. 13,14 The rate constant is not the only relevant quantity defining thermionic emission. Additional and qualitatively very instructive information is provided by the kinetic energy released distribution (KERD). ...
... The s-wave threshold detachment of OH − has been extensively studied through photodetachment [27,28] and deviations from the Wigner threshold law have been observed due to the electron-dipole interaction [29,30]. With its large rotational constant, OH − has also been used to probe the rotational thermalization by buffer gas cooling [26,31] and in cryogenic storage rings [32,33]. In buffer gas at low temperatures, significant deviations of the rotational temperature from the thermal bath have been seen [34]. ...
... Knockout-driven fragmentation has been identified in numerous experimental and theoretical studies of PAHs and fullerenes colliding with atoms and ions [27][28][29]31,32 . The most distinct fingerprint of these processes are fragments that have lost a single carbon atom, such as C 59 and C 23 H x fragments from C 60 and coronene (C 24 H 12 ) precursors, respectively 26,30 . In addition to these processes being observed with isolated molecules in the gas phase, knockout-driven fragmentation has also been shown to induce effective bond-forming reactions in cold, loosely bound clusters of such molecules that serve as laboratory analogs to small interstellar grains [33][34][35] . ...
... The lines in Fig. 4 show fits to this functional form. Powerlaw decay curves over time are commonly observed from the spontaneous decay of ensembles of hot molecular ions or clusters with broad internal energy distributions and have been reported for a wide range of systems 39,[42][43][44][45][46][47][48] . This typically occurs when a diverse ensemble of decaying units with many different time constants coexist. ...