We combine cryogenic storage of fullerene anions up to minutes with laser photo-detachment spectroscopy and measure the electron affinities to be 2.684(3) eV for C60 and 2.7665(3) eV for C70, which settle long-standing issues concerning these values. We find that C−70 cools more efficiently than C−60 and that this is due to differences in photon emission from electronically excited states populated by inverse internal conversion (recurrent fluorescence). We also find that intramolecular vibrational redistribution is no longer effective at low internal energies of C−60 or C−70. Radiative cooling becomes extremely slow below intramolecular vibrational redistribution decoupling energies of 0.32(2) and 0.13(3) eV for C−60 and C−70, respectively.

We measured the thresholds for photodetachment from the first and second excited rotational levels of CH− to the lowest vibrational, rotational, and fine-structure level of CH to be E1 = 1.213 ± 0.002 eV and E2 = 1.206 ± 0.002 eV, respectively. Based on these measurements and the rigid rotor approximation, we arrive at an electron affinity of EA = E1 + 1/2 (E1 − E2 ) = 1.217 ± 0.002 eV. This value deviates from earlier experimental results but agrees with the calculation by Feller [J. Chem. Phys. 144, 014105 (2016)]. In the present experiment, we stored ensembles of initially hot CH− in the cryogenic ion-beam storage ring Double ElectroStatic Ion-Ring ExpEriment (DESIREE) for tens of seconds such that the vast majority of the ions were in the few lowest excited rotational levels of the electronic and vibrational ground state.We identified the initial states for photodetachment channels with threshold energies E1 and E2 by comparing the time dependences of measured photodetachment signals with radiative rotational-cooling rates calculated using the literature values of the dipole moment of CH−. The conditions of a few occupied rotational levels are superior to those of previous studies of this system and an important step toward future studies with an all-rotational-ground-state ion beam.

Negative ions are unique quantum systems where electron correlation plays a decisive role in determining their properties. The lack of optically allowed transitions prevents traditional optical spectroscopy and the electron affinity is, therefore, for most elements, the only atomic quantity that can be determined with high accuracy. In this work, we present a high-precision experimental determination of the electron affinity of cesium. A collinear laser-ion beam apparatus was used to investigate the partial photodetachment cross section for the cesium anion, leaving the neutral atom in the 6p 2P3/2 excited state. A resonance ionization scheme was used to obtain final-state selectivity, which enabled the investigation of a sharp onset of the cross section associated with a Wigner s-wave threshold behavior. The electron affinity was determined to be 0.471 598 3(38) eV.

Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample corresponding to 139 fb^-1 of proton-proton collisions at a centre-of-mass energy of root s = 13TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers Q. The strong coupling constant alpha(s) is extracted as a function of Q, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of alpha(s)( mZ) = 0.1175 +/- 0.0006 (exp.)(+0.0034) (-0.0017) (theo.), while the global fit to the asymmetry distributions yields alpha(s)(m(Z)) = 0.1185 +/- 0.0009 (exp.)(+0.0025)(-0.0012)(theo.).

We have studied the stability of the smallest long-lived all carbon molecular dianion () in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes—6 orders of magnitude longer than established from earlier experiments on . This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for →+e⁻ separation.

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 calculating slow decays and the need for benchmark quality experiments.

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 optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for ¹⁶O.

The lifetime of the ³P₀ state of Bi⁻ has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of 16.0±0.5 s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.

In this thesis, experiments with negative ions performed at the DESIREE facility are presented. DESIREE consists of two electrostatic storage rings operated at 13 K. The low temperature in combination with a low pressure allows for storage times of the negative ion beams to be up to several hours. This unique feature is to advantage in the development of a new method for high-precision measurements of electron affinities and binding energies of excited states of negative ions. In this method, ions are stored in the one of the two storage rings of DESIREE, and a high-power laser is applied to photodetach ions in the excited state. These excited states are often very long-lived for negative ions and the photodetachment signal from these states are a major source of background, which dominates the uncertainties, in threshold spectroscopy experiments. By removing the ions in the excited state, threshold photodetachment spectroscopy can be performed with almost no background below the photodetachment threshold. This allows the threshold energy to be determined with a very high precision.

The new method is demonstrated by performing measurements of the electron affinities of ¹⁶O and ¹⁸O. The obtained uncertainty in the electron affinity of ¹⁶O is a tenfold improvement in accuracy compared to previous measurements and the resulting electron affinity is the most accurately measured electron affinity of any element to date. In addition to the electron affinity, the fine-structure splitting of the ground state is also measured for both isotopes. From the measured electron affinities, the isotope shift in the ¹⁸O and ¹⁶O electron affinity is determined with a high accuracy. This shift is a quantity not only relevant in atomic physics but also of great interest in nuclear physics.

In addition to the high-precision electron affinity measurements, the possibility to store ions for a long time is utilized to perform measurements of lifetimes of excited states in negative ions. Measurements are presented where excited states in Ir^-, Bi^-, and CH^- are studied. Lifetimes ranging from 100 ms up to 5000 s are observed.

The properties of atomic negative ions are to a large extent determined by electron-electron correlation which makes them an ideal testing ground for atomic many-body physics. In this paper, we present a detailed experimental and theoretical study of excited states in the negative ion of iridium. The ions were stored at cryogenic temperatures using the double electrostatic ion ring experiment facility at Stockholm University. Laser photodetachment was used to monitor the relaxation of three bound excited states belonging to the [Xe] 4f(14)5d(8)6s(2) ionic ground configuration. Our measurements show that the first excited state has a lifetime much longer than the ion-beam storage time of 1230 +/- 100 s. The binding energy of this state was measured to be 1.045 +/- 0.002 eV. The lifetimes of the second and third excited states were experimentally determined to be 133 +/- 10 and 172 +/- 35 ms, respectively. Multiconfiguration Dirac-Hartree-Fock calculations were performed in order to extract binding energies and lifetimes. These calculations predict the existence of the third excited bound state that was detected experimentally. The computed lifetimes for the three excited bound states agree well with the experimental results and allow for a clear identification of the detected levels.