We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state to the ground state. On plotting vertex-type populations as a function of time, we can characterize the relaxation, which occurs in two stages, namely a string and a domain regime. Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations.

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The A 1A′←X 1A1 electronic transition of the propargyl cation H2C3H+ with the origin band at 267.8(2) nm has been identified in a neon matrix at 5 K. The frequencies of the two modes excited in the upper state are 667(50) and 1629(50) cm−1 and imply a reduction of symmetry from C2v in the ground state to Cs in the excited state. The most intense IR mode of the propargyl cation is observed at 2079.9(1.0) cm−1 and for the cyclopropenyl cation at 3130.4(1.0) cm−1. Ab initio calculations on the excited states of the two isomer cations support the assignment and explain why the electronic transition could not be observed for the cyclic species; it lies below 200 nm. The A 2A″←X 2B1 and B 2A′←X 2B1 absorptions of the neutral propargyl radical have also been observed with origin bands at 351.9(2) and 343.0(2) nm, respectively. These results provide the basis for the study of these astrophysically interesting C3H3+ species in the gas phase.

Erratum: "Electronic absorption spectra of carbon chain anions C 2n − (n=4-7) in neon matrices" [J.The electronic absorption spectra of the even-numbered carbon molecules C 6 -C 14 have been measured in neon matrices. Bare carbon anions were produced in a cesium sputter source, mass selected, codeposited with neon at 6 K, and neutralized. The spectra show, apart from the known ͑1͒ 3 ⌺ u Ϫ ←X 3 ⌺ g Ϫ transition of linear C 6 , C 8 , and C 10 in the visible, absorption bands in the UV region. The spectral data when considered in conjunction with ab initio calculations show that the linear forms of C 6 and C 8 have the next strong ͑2͒ 3 ⌺ u Ϫ ←X 3 ⌺ g Ϫ transition with band maximum near 238 and 277 nm, respectively, whereas the band systems of C 10 , C 12 , and C 14 at 316, 332, and 347 nm are due to the monocyclic species.

We image the remnant magnetization configurations of CoFeB and permalloy nanotubes (NTs) using x-ray magnetic circular dichroism photoemission electron microscopy. The images provide direct evidence for fluxclosure configurations, including a global vortex state, in which magnetization points circumferentially around the NT axis. Furthermore, micromagnetic simulations predict and measurements confirm that vortex states can be programmed as the equilibrium remnant magnetization configurations by reducing the ratio of the NT's length and diameter.

We have performed a study of thermally driven magnetic relaxation in building blocks of artificial kagome spin ice. For room-temperature measurements, we observe that low-energy states are accessed with high efficiency, particularly in structures with strong dipolar coupling and with low thicknesses. With carefully tuned heating experiments, we demonstrate how thermally active artificial spin ice systems relax magnetically from higherenergy states and eventually fall into low-energy states. The methods applied in our work offer the possibility to observe the thermodynamics of artificial spin ice systems in real space and time, and provide a way to directly investigate the nature of complex stochastic processes.

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The electronic absorption spectra of BC, BC2 and their anions were detected in 5 K neon matrices. After mass-selected co-deposition of BC- with excess of neon, an absorption system with origin at 622.7(2) nm is observed and assigned to the A 1Σ+ ← X 1Σ+ electronic transition of BC-. Irradiation of the matrix leads to photodetachment, and the known B 4Σ- ← X 4Σ- electronic transition of BC, as well as a new one C 4Π ← X 4Σ- with origin at 291.0(2) nm, are observed. Measurements with mass-selected B lead to the identification of the A 1Π ← X 1Σ+ electronic transition of linear B at 432.2(2) nm. Subsequent neutralization leads to the appearance of two new systems with origin at 851.4(2) and 1587.8(2) nm of either linear and/or cyclic BC2. In the infrared the ν1 band of linear B was observed at 1936.3(1.0) cm-1 and after irradiation the ν2 band of cyclic BC2 at 1196.8(1.0) cm-1.