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On March 25th 2019, the Belle II detector recorded the first collisions delivered by the SuperKEKB accelerator. This marked the beginning of the physics run with vertex detector. The vertex detector was aligned initially with cosmic ray tracks without magnetic field simultaneously with the drift chamber. The alignment method is based on Millepede II and the General Broken Lines track model and includes also the muon system or primary vertex position alignment. To control weak modes, we employ sensitive validation tools and various track samples can be used as alignment input, from straight cosmic tracks to mass-constrained decays. With increasing luminosity and experience, the alignment is approaching the target performance, crucial for the first physics analyses in the era of Super-BFactories. We will present the software framework for the detector calibration and alignment, the results from the first physics run and the prospects in view of the experience with the first data.

The Belle II experiment features a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric e+e− collider at KEK in Tsukuba, Japan. The accelerator completed its first phase of commissioning in 2016, and the Belle II detector saw its first electron-positron collisions in April 2018. Belle II features a newly designed silicon vertex detector based on double-sided strip layers and DEPFET pixel layers. A subset of the vertex detector was operated in 2018 to determine background conditions (Phase 2 operation). The collaboration completed full detector installation in January 2019, and the experiment started full data taking. This paper will report on the final arrangement of the silicon vertex detector part of Belle II with a focus on online monitoring of detector conditions and data quality, on the design and use of diagnostic and reference plots, and on integration with the software framework of Belle II. Data quality monitoring plots will be discussed with a focus on simulation and acquired cosmic and collision data.

The CH4 oxidation performance of Cu‐chabazite zeolites characterized by distinct Si/Al ratios and Cu loadings has been studied and the observed variations in reactivity have been correlated to the differences in the nature of the formed active centers. Plug flow reactor tests, in situ Fourier‐transform infrared, and X‐ray absorption spectroscopy demonstrate that a decrease in Cu loading shifts the reactivity/redox profile to higher temperatures and increases the CH3OH selectivity and Cu‐efficiency. In situ electron paramagnetic resonance, Raman, ultraviolet‐visible, Fourier‐transform infrared, and photoluminescence spectroscopies reveal that this behavior is associated with the presence of monomeric Cu active sites, including bare Cu2+ and [CuOH]+ present at low Si/Al ratio and Cu loading. Formation of two distinct [Cu2(μ‐O)]2+ moieties at higher Si/Al ratio or Cu loading forces these trends into the opposite direction. Operando electron paramagnetic resonance and ultraviolet‐visible spectroscopy show that the apparent activation energy of monomeric Cu active species decreases with increasing Si/Al ratio, whereas the one of dimeric centers is unaffected. [ABSTRACT FROM AUTHOR]

Electron Nuclear Double Resonance (ENDOR) spectroscopy is an EPR technique to detect the nuclear frequency spectra of hyperfine coupled nuclei close to paramagnetic centres, which have interactions that are not resolved in continuous wave EPR spectra and may be fast relaxing on the time scale of NMR. For the common case of non-crystalline solids, such as powders or frozen solutions of transition metal complexes, the anisotropy of the hyperfine and nuclear quadrupole interactions renders ENDOR lines often several MHz broad, thus diminishing intensity. With commonly used ENDOR pulse sequences only a small fraction of the NMR/ENDOR line is excited with a typical RF pulse length of several tens of μs, and this limits the sensitivity in conventional ENDOR experiments. In this work, we show the benefit of chirped RF excitation in frequency domain ENDOR as a simple yet effective way to significantly improve sensitivity. We demonstrate on a frozen solution of Cu(II)-tetraphenylporphyrin that the intensity of broad copper and nitrogen ENDOR lines increases up to 9-fold compared to single frequency RF excitation, thus making the detection of metal ENDOR spectra more feasible. The tunable bandwidth of the chirp RF pulses allows the operator to optimize for sensitivity and choose a tradeoff with resolution, opening up options previously inaccessible in ENDOR spectroscopy. Also, chirp pulses help to reduce RF amplifier overtones, since lower RF powers suffice to achieve intensities matching conventional ENDOR. In 2D TRIPLE experiments the signal increase exceeds 10 times for some lines, thus making chirped 2D TRIPLE experiments feasible even for broad peaks in manageable acquisition times. [ABSTRACT FROM AUTHOR]

Continuous-wave electron paramagnetic resonance (EPR) spectroscopy at 35 GHz is an essential cornerstone in multi-frequency EPR studies and is crucial for differentiating multiple species in complex systems due to the improved g -tensor resolution compared to lower microwave frequencies. Especially for unstable and highly sensitive paramagnetic centers, the reliability of the measurements can be improved upon through the use of a single sample for EPR experiments at all frequencies. Besides the advantages, the lack of common availability of oversized-sample resonators at 35 GHz often limits scientists to lower frequencies or smaller sample geometries, and the latter may be non-trivial for sensitive materials. In this work, we present the design and performance of an oversized-sample 35 GHz EPR resonator with a high loaded Q value, QL , of up to 2550, well-suited for continuous-wave EPR and pulsed single-microwave-frequency experiments. The design is driven by electromagnetic field simulations, and the microwave characteristics of manufactured prototypes were found to be in agreement with the predictions. The resonator is based on a cylindrical cavity with a TE 011 mode, allowing for 3 mm sample access. The design targets that we met include high sensitivity, robustness, and ease of manufacturing and maintenance. The resonator is compatible with commercial EPR spectrometers and with helium flow, as well as with cryogen-free cryostats, allowing for measurements at temperatures down to 1.8 K. To highlight the general applicability, the resonator was tested on metal centers, as well as on organic radicals featuring extremely narrow lines. [ABSTRACT FROM AUTHOR]

Hybrid methylammonium (MA) lead halide perovskites have emerged as materials exhibiting excellent photovoltaic performance related to their rich structural and dynamic properties. Here, we use multifrequency (X-, Q-, and W-band) electron paramagnetic resonance (EPR) spectroscopy of Mn2+ impurities in MAPbCl3 to probe the structural and dynamic properties of both the organic and inorganic sublattices of this compound. The temperature dependent continuous-wave (CW) EPR experiments reveal a sudden change of the Mn2+ spin Hamiltonian parameters at the phase transition to the ordered orthorhombic phase indicating its first-order character and significant slowing down of the MA cation reorientation. Pulsed EPR experiments are employed to measure the temperature dependences of the spin-lattice relaxation T1 and decoherence T2 times of the Mn2+ ions in the orthorhombic phase of MAPbCl3 revealing a coupling between the spin center and vibrations of the inorganic framework. Low-temperature electron spin echo envelope modulation (ESEEM) experiments of the protonated and deuterated MAPbCl3 analogues show the presence of quantum rotational tunneling of the ammonium groups, allowing to accurately probe their rotational energy landscape. [ABSTRACT FROM AUTHOR]

Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and -- still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-theart magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe3)2]3, a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre--two-electron Yb-γ-Me-β-Si secondary metal--ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb--carbon bond contains some p-character, reminiscent of the so-called a-H agostic interaction. [ABSTRACT FROM AUTHOR]

The ethylene polymerization Phillips catalyst has been employed for decades and is central to the polymer industry. While Cr(III) alkyl species are proposed to be the propagating sites, there is so far no direct experimental evidence for such proposal. In this work, by coupling Surface organometallic chemistry, EPR spectroscopy, and machine learning‐supported XAS studies, we have studied the electronic structure of well‐defined silica‐supported Cr(III) alkyls and identified the presence of several surface species in high and low‐spin states, associated with different coordination environments. Notably, low‐spin Cr(III) sites are shown to participate in ethylene polymerization, indicating that similar Cr(III) alkyl species could be involved in the related Phillips catalyst. [ABSTRACT FROM AUTHOR]

Cu‐exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu‐MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet‐visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier‐transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired [CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent [CuOH]+ demonstrates that the frequently reported assumption of redox‐inert Cu2+ centers does not generally apply. The measured site‐specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential. [ABSTRACT FROM AUTHOR]