Temperature Dependent Electron Spin Resonance Research Articles

EPR studies of ferredoxin in spinach and cyanobacterial thylakoids related to photosystem I-driven NADP+ reduction.

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP+ reductase (FNR) for the reduction of NADP+ to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP+ was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a "pool" of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30K. At 50K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values gx = 2.05, gy = 1.96, and gz = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP+ photoreduction. Quantitation of the EPR signals of P700+ and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. These EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.

Thermodynamics of spin crossover in a bis(terpyridine) cobalt(II) complex featuring a thioether functionality.

In this contribution, a terpyridine-based ligand bearing a thioether functionality is used to prepare a new cobalt(II) spin crossover complex: [Co(TerpyPhSMe)2](PF6)2 (1), where TerpyPhSMe is 4'-(4-methylthiophenyl)-2,2':6',2''-terpyridine. Its structure, determined by single crystal X-ray diffraction, reveals a mer coordination of the tridentate terpyridine ligands, leading to a tetragonally compressed octahedron. Intermolecular interactions in the crystal lattice freeze the complex in the high spin state in the solid state at all temperatures, as indicated by magnetometry and Electron Paramagnetic Resonance (EPR) spectra. When dissolved in acetonitrile, however, temperature dependent electronic, 1H-NMR and EPR spectra highlight an entropy-driven spin crossover transition, whose thermodynamics parameters have been determined. This is the first report of a cobalt(II) SCO complex featuring a thioether group, allowing its implementation in chemically grown bistable monolayers and may open important perspectives for the use of such systems in molecular spintronics.

Insights into the protonation state and spin structure for the g = 2 multiline electron paramagnetic resonance signal of the oxygen-evolving complex.

In photosystem II (PSII), one-electron oxidation of the most stable oxidation state of the Mn4CaO5 cluster (S1) leads to formation of two distinct states, the open-cubane S2 conformation [Mn1(III)Mn2(IV)Mn3(IV)Mn4(IV)] with low spin and the closed-cubane S2 conformation [Mn1(IV)Mn2(IV)Mn3(IV)Mn4(III)] with high spin. In electron paramagnetic resonance (EPR) spectroscopy, the open-cubane S2 conformation exhibits a g = 2 multiline signal. However, its protonation state remains unclear. Here, we investigated the protonation state of the open-cubane S2 conformation by calculating exchange couplings in the presence of the PSII protein environment and simulating the pulsed electron-electron double resonance (PELDOR). When a ligand water molecule, which forms an H-bond with D1-Asp61 (W1), is deprotonated at dangling Mn4(IV), the first-exited energy (34 cm-1) in manifold spin excited states aligns with the observed value in temperature-dependent pulsed EPR analyses, and the PELDOR signal is best reproduced. Consequently, the g = 2 multiline signal observed in EPR corresponds to the open-cubane S2 conformation with the deprotonated W1 (OH-).

Antisites disorder mediated magnetization relaxation and polydispersity in La2NiMnO6 crystallites

Antisite disorders play a critical role in determining the magnetic ground state of the La2NiMnO6 double perovskite compounds that show multifunctional behaviours and spin-glass phases at lower temperatures. The spin-glass (SG) state and magnetization relaxation in these compounds have been studied extensively; however, the polydispersity of the SG state remains elusive. Employing ac-magnetic susceptibility χ(ω,T) and temperature-dependent electron spin resonance (ESR) spectroscopy, herein, we probe the polydispersity of the SG phase in La2NiMnO6 crystallites. We employed X-ray photoelectron spectroscopy (XPS) to -investigate the crystallite size-dependent variable fractions of Mn3+/Mn4+ (Ni2+/Ni3+) cations and their influence on completing exchange interactions. Mn-2p core-level XPS spectra suggest a dominant Mn4+ + Ni2+→Mn3+ + Ni3+ charge transfer peak that appeared as a satellite peak at lower binding energy than the Mn core-level. The observed differences in saturation magnetization (MS) as a function of crystallite size indicate the variation in the degree of antisites disorder. Competing magnetic interactions driven by mixed valence and disorder facilitate a spin-glass (SG) phase at lower temperatures. Utilizing ESR measurement across paramagnetic → competing ferro/antiferromagnetic phase, a modified g-factor that ranges from 2.050-2.037 is observed in the paramagnetic region. The line width of the ESR signals is found to be increased across the transition suggesting spin-freezing characteristics. Cole-Cole plots obtained from χ(ω,T) data indicate collective spin relaxation dynamics in the proximity of the freezing temperature. Our findings suggest the importance of the size effect and its relation with the degree of antisites disorders in these crystallites. These experimental results enable the La2NiMnO6 compound to find its possible applications in new areas of material research.

Enhanced Spin-Nuclei Couplings of Paramagnetic Azametallofullerene Hooped in Cycloparaphenylene

Azametallofullerene Y2@C79N has outstanding electron spin characteristics with potential application in the fields of magnetoreception system and precision measurement as a molecular spin probe. Herein, we report the spin modulation of Y2@C79N by means of host–guest interaction with a carbon nanoring of [12]Cycloparaphenylene ([12]CPP). By means of temperature-dependent electron paramagnetic resonance (EPR) measurements, the adjustable EPR signals of Y2@C79N⊂[12]CPP were observed, revealing the great effect of host–guest interaction on the spin and paramagnetic property of hooped Y2@C79N. The EPR signals of Y2@C79N⊂[12]CPP and pristine Y2@C79N were comparatively investigated in carbon disulfide and in solid state, and it was found that the Y2@C79N⊂[12]CPP complex exhibits enhanced spin-nuclei couplings compared to those of pristine Y2@C79N. We propose that the [12]CPP host can induce the orientation of the Y2@C79N guest, and consequently change the spin-nuclei couplings of Y2@C79N. This study would promote the creation of new molecular spin materials.

Magnetic decoupling in the triangular-lattice antiferromagnet Cu2(OH)3CHO2 studied by high-field magnetization and ESR

The high-field magnetization and electron spin resonance (ESR) are reported for the two-dimensional triangular-lattice antiferromagnet Cu2(OH)3HCO2. The compound has an antiferromagnetic (AFM) order at TN = 4.9 K with the Curie-Weiss temperature θCW = − 3.8 K. The high-field magnetization up to 50 T exhibits a metamagnetic transition at 1.7 T followed by a half-saturated ferromagnetic (FM)-like magnetization process, showing the magnetic decoupling between the Cu1 FM chain and the Cu2 AFM chain. The unsaturated magnetization at 50 T serves as an evidence of much larger AFM exchange in the Cu2 chain. The temperature-dependent ESR spectra are in line with the development of magnetic correlations and AFM ordering. The observed ESR modes below TN originate from the AFM resonances of the antiferromagnetically coupled Cu1 FM chains. The zero-field gap of 111 GHz and the zero-frequency field of 2.4 T suggest the presence of significant magnetic anisotropy.

Low-temperature magnetic order rearrangement in the layered van der Waals compound MnPS3

To stabilize the long-range magnetic ordering in two-dimensional (2D) materials is a challenge from both fundamental and application points of view. It is difficult to be realized due to the delicate competition between thermal energy, magnetic exchange energy, and spin frustration. Here we study the temperature and field effects on the spin structure of two-dimensional van der Waals system ${\mathrm{MnPS}}_{3}$ using dc magnetic susceptibility and electron spin resonance (ESR) techniques. Clear development of three-step transitions was observed in the in-plane susceptibility. A low-temperature plateau from 78 to 38 K can be related to the Heisenberg antiferromagnetic (HAFM) ordering with spins pointing to the $z$ direction. Following, a sharp rising after the plateau suggests a transition into the $XY$ system. The rising slope slows down at 30 K indicating a transition into another phase, possibly a vortex-antivortex state. By fitting the temperature-dependent ESR parameters with the Berezinskii-Kosterlitz-Thouless (BKT) model in the range 100--300 K, we propose a spin 2D system with the vortex-antivortex structure below the HAFM transition. Susceptibility and ESR data show that the application of a high field along the $z$ direction destroys both the $XY$ phase and the BKT transition, reconciling to the scenario of a topological phase transition at zero field.

Microwave response of chiral magnetic soliton in Yb(Ni1−xCux)3Al9

A chiral soliton lattice (CSL) is a topological spin-texture that has potential applications in next-generation spintronic devices. In this work, we performed angle-dependence of magnetization and electron spin resonance (ESR) investigations on the CSL host Yb(Ni1−xCux)3Al9 with x = 0.06 (YNCA). The angle-dependent magnetization reveals a peculiar variable magnetic anisotropy. The maximum magnetization axis is parallel to the ab-plane below the field of ∼35.7 kOe while shifts to the c-axis at higher fields. The microwave responses of the CSL helicoid and ferromagnetic resonance (FMR) of the forced ferromagnetic state (FFM) are observed and appear as two resonance lines on ESR spectra with the highest intensities in the ab-plane. When the external field is rotated from H⊥c to H//c, the resonance field Hr1 corresponding to the CSL helicoid decreases while Hr2 correlated with the FMR increases. Furthermore, the temperature-dependent ESR shows that the CSL persists until 15 K much higher than TC (6.4 K), which suggests a precursor phenomenon. The microwave response in YNCA provides a powerful tool for modulating and researching the CSL.

Evidence for increased metallicity arising from carbon-sulfur bonding and amorphization effects in sulfur-doped pyrolytic graphite

We report a novel investigation of the electronic and magnetic properties of exfoliated lamellae of highly-oriented-pyrolytic-graphite (HOPG) doped with great excess of sulfur. The sulfur-doping process was achieved through annealing at T ~ 250 °C, ~500 °C and ~990 °C. The obtained lamellae were investigated by employing transmission electron microscopy (TEM), Raman point/map spectroscopy and temperature dependent electron paramagnetic resonance (T-EPR). HRTEM analyses of samples doped at T ~ 990 °C revealed an unusual amorphization-effect arising within hexagonal moiré superlattices as a consequence of the sulfur-doping. Complete amorphization was found at T ~ 500 °C. Raman-spectroscopy point/mapping analyses highlighted a dominant carbon-sulfur-band, appearing at Raman-Shifts of 1450 cm−1. T-EPR of heavily doped samples revealed presence of shifts in the position of the π-electron differential absorption feature together with an anomalous signal broadening at Tdoping ~ 500 °C (from g ~ 1.99 to g ~ 2.10), while zero field cooled (ZFC) and field cooled FC superconducting quantum interference device (SQUID) magnetometry from 2 K to 300 K revealed a critical percolative ferromagnetic temperature at T ~ 25 K and the absence of superconductive transitions. Density functional theory (DFT) calculations applied to a Bernal (AB stacked) bilayer-graphene-system in presence of sulfur-bonding revealed a significant variation of the system-metallicity. We highlight the appearance of insulating states (E-gap of 0.325 eV) at sulfur concentrations of ~1%, which then vanish at ~5.5% of sulfur-doping, due to an enhanced degree of system-metallicity and a modification of the π-bonding- and antibonding-signals.

Two-sublattice description of the dimer-trimer chain compound Li2Cu5Si4O14 : High-field magnetization and ESR studies

We carried out high magnetic field magnetization and electron spin resonance (ESR) measurements for the alternating dimer-trimer chain compound ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$. The magnetization curve measured at 2 K exhibits a spin-flop transition at 2.6 T followed by a nonlinear increase in magnetization at high field up to 55 T. The antiferromagnetic ordering at ${T}_{\mathrm{N}}=22\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is well characterized by the temperature-dependent ESR spectra, and the anisotropic $g$ factors at the paramagnetic phase are determined. Intriguingly, our frequency-dependent ESR spectra at 2 K reveal the development of two collinear antiferromagnetic sublattices with biaxial anisotropy, which is quite unusual because ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$ contains five sublattices. Thus, ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$ is three-dimensionally ordered and its magnetism might be described by a pseudo-two-sublattice model composed of antiferromagnetically coupled dimer-trimer groups (\ensuremath{\uparrow}\ensuremath{\uparrow}, \ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}) and (\ensuremath{\downarrow}\ensuremath{\downarrow}, \ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\downarrow}).

Interplay of edge/screw dislocations and enhanced magnetism in exfoliated pyrolytic graphite with distorted hexagonal moiré superlattices

The recent observation of enhanced magnetic signals in post-exfoliated lamellae of highly oriented pyrolytic graphite (HOPG) has attracted an important attention. It has been suggested that such a magnetization enhancement may originate from exfoliation-induced structural transitions, possibly involving rhombohedral domain and/or topological disorder formation. Further studies are therefore needed in order to elucidate the origin of such magnetic effects. Here we report a novel investigation on the structural and magnetic properties of multiple lamellae exfoliated from the inner regions of a main HOPG sample. HRTEM revealed moiré-superlattices with coexisting-periodicity-gradients ∇D∼13.1 nm to 16.2 nm, D∼ 2.6 nm in lamella-1, ∇D∼ 30 nm to 36 nm in lamella-2 and ∇D∼ 10.4 nm to ∼ 12.0nm, 3.1 nm in lamella-3. Exfoliation-induced distortion effects of the moiré-areas were investigated by employing HRTEM and Fourier transform analyses. We describe this effect on the basis of the Burgers–Bragg–Read–Shockley model with contributions arising from both I) edge dislocations (tilting angle θc ≠ 0, altered by the tape-exfoliation) and II) screw dislocations (twisting angle θtwist ≠ 0). Extended temperature dependent electron paramagnetic resonance (T-EPR) investigations revealed important shifts in the position of the π-electron differential absorption feature. The reported results are possibly an indicator of defect-induced electron correlation effects. Superconducting quantum interference device (SQUID) magnetometry measurements revealed an unusual magnetization-enhancement interpreted as a consequence of the exfoliation process.

In-situ Insights into trap attributions in Fe3+-activated long persistent phosphors

Here, a novel NIR afterglow center of Fe3+ is proposed, and a long persistent phosphor of SrAl12O19: Fe3+ is successfully fabricated. Some in-situ characterizations, including temperature-dependent electron paramagnetic resonance (EPR) spectra and thermoluminescence (TL) spectra of Al2O3 and SrCO3 raw materials, support the fact that the substitution of Fe3+ to Al3+ creates a trap with the negative effective charge by binding an electron around [AlFe]. Further, the existence of isoelectronic trap-cluster (AlFe-VO) endows a bright emission band that appeared in the range of 750–1000 nm with an afterglow duration of >2 h. Notably, these analyses in the aspect from the influence of raw materials on afterglow properties are very rarely found in the searchable reports. This top-down investigation route reveals the possibility of perfecting the research skills on the afterglow mechanism from the fountainhead and may offer a wide-range understanding of the trapping and de-trapping process of long persistent phosphors.

Electron spin resonance study of proton-irradiated topological insulator Bi2Se3 nanoparticles

We have studied the proton-irradiation effects on the topological insulator Bi2Se3 nanoparticles by means of electron spin resonance (ESR) measurements. The ESR signals from the hydrogen-doped Bi2Se3 nanoparticles, ascribed to the metallic surface of the topological insulator, were enhanced at high enough proton irradiation doses, which was explained by the enhanced surface effect. Our density functional theory calculations indicated that the hydrogen defects act as donors whose transition levels are in the conduction band. Thus, weak potential fluctuations are taken to be responsible for the small activation energy of ~5 meV, obtained from the temperature-dependent ESR intensity.

N^N Pt(II) Bisacetylide Complexes with Oxoverdazyl Radical Ligands: Preparation, Photophysical Properties, and Magnetic Exchange Interaction between the Two Radical Ligands.

To study the effect of a stable radical on the photophysical properties of a phosphorescent Pt(II) coordination framework and the intramolecular magnetic interaction between radical ligands in the N^N Pt(II) bisacetylide complexes, we prepared a series of N^N Pt(II) bis(acetylide) complexes with oxoverdazyl radical acetylide ligands. The linker between the Pt(II) center and the spin carrier was systematically varied, to probe the effect on the sign and magnitude of the spin exchange interactions between the radical ligands and photophysical properties. The complexes were studied with steady-state and femtosecond/nanosecond transient absorption spectroscopy, continuous-wave electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) computations. The transient absorption spectral studies show that the doublet excited state of the radicals are short-lived (τD ≈ 2 ps) and nonfluorescent. Moreover, the intrinsic long-lived triplet excited state (τT = 1.2 μs) of the Pt(II) coordination center was efficiently quenched by the radical (τT = 6.9 ps for one representative radical Pt(II) complex). The intramolecular magnetic interaction between the radical ligands through the diamagnetic Pt(II) atom was studied with temperature-dependent EPR spectroscopy; antiferromagnetic exchange interaction (-J S1S2, J = -5.4 ± 0.1 cm-1) for the complex with the shortest radical-radical distance through bridge fragments was observed. DFT computations give similar results for the sign and magnitude of the J values. For complexes with larger inter-radical distance, however, very weak coupling between the radical ligands was observed (|J| < 0.7 cm-1). Our results are useful for the study of the effect of a radical on the photophysical properties of the phosphorescent transition-metal complexes.

Radiation induced defects in timolol: temperature dependent electron paramagnetic resonance spectroscopy analysis

Ionizing radiation-induced antihypertensive drug timolol in powder form was studied by means of electron paramagnetic resonance (EPR) technique as a function of temperature. The effect of temperature on EPR linewidth, intensity and spectra was investigated. The room temperature EPR spectra of ionizing radiation-induced timolol were recorded in dimethyl sulfoxide solution at a frozen state. The first-order kinetic mechanism rate constant of timolol was calculated. The findings on all EPR experimental data indicated that ionizing radiation-induced stable-free radical species on timolol are characterized by g = 2.0027.

High Magnetic Field ESR in S = 1 Skew Chain Antiferromagnet Ni2V2O7 Single Crystal

We report electron spin resonance (ESR) in S = 1 skew chain antiferromagnet Ni2V2O7, which exhibits a spin-flop transition and a well-defined 1/2 magnetization plateau. The antiferromagnetic (AFM) ordering at TN = 7 K can be reflected by the temperature-dependent ESR spectra at low frequency for the easy axis. At 2 K, at the spin-flop transition fields along the easy a and b axes, anomalies are observed from the frequency‒field relationship. However, these modes cannot be understood by the conventional two-sublattice AFM resonance theory with uniaxial anisotropy. For the easy b axis, an unusual resonance mode is observed and its resonance field increases with decreasing frequency. This ESR mode becomes softening at ~8 T, corresponding to the onset of the 1/2 magnetization plateau.

Electrical and structural characterization of shallow As acceptors in natural p-type 2H-MoS2

Hexagonal molybdenite (MoS2) is one of the most promising two-dimensional (2D) semiconductors, known with n-type and p-type conduction, with possible applications in electronic, opto-electronic, and spintronic devices. In this work, highly pure geological samples of 2H-MoS2 were investigated by temperature-dependent electron paramagnetic resonance (EPR) and Hall effect measurements. The low-temperature (&amp;lt;55 K) EPR spectra were consistently explained as holes (S = 1/2) trapped on shallow As acceptors on sulfur sites leading to a four-line hyperfine-split spectrum (75As: I = 3/2, 100%) in axial symmetry and with a concentration of 5(1) ppm (∼2 × 1017 cm−3). Electrical measurements indicate p-type conduction with a free carrier concentration of about 5 × 1017 cm−3 at room temperature and an ionization energy of 52 meV associated with the shallow As acceptors, which is consistent with the ionization energy determined from the hydrogenic model of shallow acceptors in 2H-MoS2. These values are in strong contrast to the unrealistic value of 0.7 meV reported in the literature obtained from the analysis of temperature-dependent EPR measurements. Possible explanations are related to temperature-dependent spin-lattice relaxation effects, affecting strongly EPR line intensities and making impossible their use in obtaining the ionization energy.

Investigations of the temperature-dependent electron paramagnetic resonance spectra and local structures for a cobalt(II) porphyrin complex within a metal-organic framework.

The interaction between an adsorbed CO molecule and the unsaturated coordinated Co2+ center in the metal-organic framework (MOF) PCN-224 is investigated by analyzing the electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) and the adsorption energies at various temperatures. Six- and five-coordinated octahedral models (four planar N with two and one axial CO molecules, respectively) are constructed to simulate the local structures of the Co2+ centers at different temperatures. Because of the Jahn-Teller effect of the Co2+ centers, the C2-Co-N4 and C-Co-N4 combinations undergo different tetragonal elongation distortions along the C4 axis, characterized by the relative elongation ΔZ and displacement ΔZ' of Co2+ at different temperatures. Given the agreement between the calculated and experimental EPR parameters, as well as the adsorption properties, the six- and five-coordinated models are regarded as suitable for low- and high-temperature systems, respectively. These studies may be helpful to understand the properties of similar MOFs with adsorbed molecules under the effect of ambient temperature.

Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo2F7

We report high-frequency/high-field electron spin resonance (ESR) and high-field magnetization studies on single crystals of the bond-disordered pyrochlore NaCaCo$_2$F$_7$. Frequency- and temperature-dependent ESR investigations above the freezing temperature $T_f \sim 2.4$ K reveal the coexistence of two distinct magnetic phases. A cooperative paramagnetic phase, evidenced by a gapless excitation mode, is found as well as a spin-glass phase developing below 20 K which is associated with a gapped low-energy excitation. Effective $g$-factors close to 2 are obtained for both modes in line with pulsed high-field magnetization measurements which show an unsaturated isotropic behavior up to 58 T at 2 K. In order to describe the field-dependent magnetization in high magnetic fields, we propose an empirical model accounting for highly anisotropic ionic $g$-tensors expected for this material and taking into account the strongly competing interactions between the spins which lead to a frustrated ground state. As a detailed quantitative relation between effective $g$-factors as determined from ESR and the local $g$-tensors obtained by neutron scattering [Ross et al., Phys. Rev. B 93, 014433 (2016)] is still sought after, our work motivates further theoretical investigations of the low-energy excitations in bond-disordered pyrochlores.

Thermal stability and temperature dependent electron spin resonance characteristics of the As acceptor in geological 2H-MoS2

Electron spin resonance (ESR) results are presented on the thermal stability and temperature dependence of the ESR spectral characteristics of the As acceptor dopant (As substituting for S site) in geological 2H-MoS2. Under sequential isochronal heating in H2 (1.1 atm), the As dopant density is found to remain unaffected for anneal temperatures (Tans) up to 525 °C, above which the density moderately decreases (∼3 times) for Tan → 840 °C. In turn, vacuum annealing is seen to result in a gradual increase (2–3 times) of the As acceptor density for Tan increasing from 400 °C → 840 °C, pointing to a positive ‘regain’ of misconfigured As impurities in pristine geo-MoS2. Finally, meticulous monitoring of the ESR signal intensity versus tempertaure at X-band confirms the previously inferred As acceptor activation energy of 0.7 ± 0.2 meV at K-band. The appropriateness of the latter ESR probing and analysis approach has been consolidated by application to the archetypal case of decoupled P donors in n-Si, resulting in an ESR-determined activation energy (42 ± 4 meV) well in agreement with the generally accepted one. In light of these findings, As is confirmed as a promising candidate for stable covalently bonded p-type doping of MoS2.