Separation of long-lived radionuclides from high active nuclear waste

The management of vitrified high activity waste issued from the reprocessing of spent nuclear fuel is often made questionable by the presence within this waste of long-lived radionuclides (LLRNs). New management scenarios of this waste are under study at the CEA since the beginning of the 1990s, involving the development of separation processes for some LLRNs. Six LLRNs are the targets of these studies; they are: (i) the minor actinides: neptunium, americium and curium; (ii) the fission products: technetium, iodine and caesium. The present paper highlights the main achievements of the research performed at the CEA in this field. To cite this article: C. Madic et al., C. R. Physique 3 (2002) 797–811.     

New conditionings for separated long-lived radionuclides

Long-lived radionuclides such as I¹²⁹, Cs¹³⁵ and minor actinides can be incorporated in crystalline structures of several specific materials with high chemical durability. Apatites, zirconolite, monazites, thorium phosphate-diphosphate and hollandite are being studied at the CEA and among a scientific research group called NOMADE. A first step is devoted to the scientific feasibility dealing with elaboration and characterization of non-radioactive materials and studies of their chemical durability and radiation stability. Development of apatite for iodine and minor actinides, zirconolite for minor actinides, monazite for trivalent actinides and thorium phosphate–diphosphate for tetravalent actinides has reached the scientific feasibility. Cs conditioning in hollandite and phosphate minerals needs further studies. To cite this article: C. Guy et al., C. R. Physique 3 (2002) 827–837.     

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds

The elusive monosubstituted diruthenium complexes [Ru₂Cl(DAniF)(O₂CMe)₃] (1), [Ru₂Cl(DPhF)(O₂CMe)₃] (2), [Ru₂Cl(D-p-CNPhF)(O₂CMe)₃] (3), [Ru₂Cl(D-o-TolF)(O₂CMe)₃] (4), [Ru₂Cl(D-m-TolF)(O₂CMe)₃] (5), [Ru₂Cl(D-p-TolF)(O₂CMe)₃] (6) and [Ru₂Cl(p-TolA)(O₂CMe)₃] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal–metal bonded dinuclear compounds (DAniF⁻ = N,N′-bis(4-anisyl)formamidinate; DPhF⁻ = N,N′-diphenylformamidinate; D-p-CNPhF⁻ = N,N′-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF⁻ = N,N′-bis(2/3/4-tolyl)formamidinate; p-TolA⁻ = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1–7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2–6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted compounds.     

High-efficiency degradation catalytic performance of a novel Angelica sinensis polysaccharide-silver nanomaterial for dyes by ultrasonic cavitation

Currently, the polluted wastewater discharged by industry accounts for the major part of polluted bodies of water. As one of the industrial wastewaters, dye wastewater is characterized by high toxicity, wide pollution, and difficulty in decolorization degradation. In this paper, a novel composite nanomaterial catalyst of silver was prepared by using Angelica sinensis polysaccharide (ASP) as a reducing and stabilizing agent. And the optimum reaction conditions explored are V_AgNO3 = 5 mL (300 mM) and v_ASP = 7% (w/v) for 6 h at 90 °C. In addition, the ASP-Ag nanocatalyst was characterized by several techniques. The results demonstrated that ASP-Ag nanoparticles were successfully synthesized. Degradation rate, which provides a numerical visualization of the percentage reduction in pollutant concentration. With the wrapping of ASP, the ultrasonic catalytic degradation rates of different organic dyes including rhodamine B (RB), methylene blue (MB), and methyl orange (MO) were from 88.2%, 88.7%, and 85.2% to 96.1%, 95.2% and 93.5% at room temperature, respectively. After the experiments, when c_dyes = 10 mg/L, the highest degradation rate can be observed under c_APS-AgNPs = 10 mg/L with the most powerful cavitation frequency f = 59 kHz. The effect of ultrasonic frequency on the acoustic pressure distribution in the reactor was investigated by using COMSOL Multiphysis^@ software to propose the mechanism of ultrasonic degradation and the mechanism was confirmed by OH radical trapping experiments. It indicates that OH produced by the ultrasonic cavitation effect plays a determinant role in the degradation. And then, the intermediate products of the dye degradation process were analyzed by gas chromatography and mass spectrometry (GC–MS), and the possible degradation processes of dyes were proposed. The resulting products of degradation are SO₄²⁻, NH₄⁺, NO₃⁻, N₂, CO₂ and H₂O. Finally, the recycling degradation experiments showed that catalyst maintains a high degradation rate within reusing 5 cycles. Thus, this catalyst is highly efficient and recyclable.     

2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-based donor-acceptor type copolymers for photovoltaic cells

Alternating donor-acceptor type copolymers, poly[{5,11-di(9′-heptadecanyl)indolo[3,2-b]carbazole}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl}] (PIC-TZ) and poly[{6,6′,12,12′-tetraoctylindeno[1,2-b]fluorene}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl}] (PIF-TZ), were synthesized and examined for applications in polymeric photovoltaic cells. The polymers have a fused coplanar main backbone with good planarity for intermolecular packing and high charge mobility. The indolocarbazole and indenofluorene units contain two or four binding sites for alkyl substituents that have pronounced solution processiblity compared to the carbazole and fluorene moieties. The number-average molecular weights (M_n) of the synthesized polymers were determined to be 11,000 g/mol (PDI = 2.27) for PIC-TZ, and 17,000 g/mol (PDI = 1.77) for PIF-TZ. The optical band gap of PIC-TZ and PIF-TZ in film was determined to be 2.14 eV and 2.21 eV, respectively, and an electrochemical study confirmed the desirable HOMO/LUMO levels of the copolymers, which enabled efficient electron transfer and a high open circuit voltage (V_OC) when blending them with fullerene derivatives. The space charge limited current mobility measurements showed a hole mobility of 10⁻³ cm² V⁻¹ s⁻¹ for the copolymers. When the polymers were blended with [6,6]phenyl-C₆₁-butyric acid methyl ester (PCBM), PIC-TZ showed the best performance with V_OC, short-circuit current and power conversion efficiency of 0.86 V, 4.16 mA/cm² and 1.64%, respectively, under AM 1.5G illumination conditions (100 mW cm⁻²).     

Synthesis,characterization and luminescence study of dimethyl[N-arylmethylenethiobenzahydrazonato]indium

Five dimethylindium complexes of type Me₂InL [L = N-(4-methoxy)benzylidenethiobenzahydrazonato (1), N-(3,4-dimethoxy)benzylidenethiobenzahydrazonato (2), N-(4-N,N-dimethylamino)benzylidenethiobenzahydrazonato (3), N-(2-naphthyl)methylene thiobenzahydrazonato (4) and N-(9-anthryl)methylenethiobenzahydrazonato (5)] have been synthesized by reaction of trimethylindium with appropriate N-arylmethylenethiobenzahydrozones. The complexes obtained have been characterized by elemental analysis, ¹H NMR, IR and mass spectroscopy. Compounds 1–5 emit blue colors at λ_max = 432–479 nm when irradiated by UV light. The electroluminescent (EL) properties of 1–5 were examined by fabricating EL devices using 1–5 as emitter, respectively. The EL bands are located in the green region (513–578 nm).     

UV–Vis and NMR spectroscopic investigations on effective and selective non-covalent interactions between fullerenes and calix[6]arene

Ground state non-covalent interactions between a macro cyclic calixarene receptor, namely, 4-tert-butylcalix[6]arene (1), and fullerenes (C₆₀ and C₇₀) were studied in toluene medium by absorption spectrophotometric method. Absorption band due to the charge transfer (CT) transition have been observed in the visible region between fullerenes and 1. Utilizing the CT absorption bands, various important physicochemical parameters like oscillator strength, resonance energy, transition dipole strength of the fullerene-1 complexes and ionization potential of 1 is determined in present investigations. From Jobs method of continuous variation, it is observed that both C₆₀ and C₇₀ form stable 1:1 complexes with 1. The most fascinating feature of the present study is that 1 binds selectively C₇₀ compared to C₆₀ as obtained from binding constant (K) data of C₆₀–1 (K_C60–1) and C₇₀–1 (K_C70–1) complexes, i.e., K_C60–1 = 32,400 dm³·mol^? 1 and K_C70–1 = 110,000 dm³.mol^? 1 and selectivity (K_C70–1/K_C60–1) = 3.4. ¹H NMR analysis provides very good support in favor of strong binding between C₇₀ and 1.     

2 billion year old natural analogs for nuclear waste disposal: the natural nuclear fission reactors in Gabon (Africa)

Two billion years ago, the increase of oxygen in atmosphere and the high ²³⁵U/²³⁸U uranium ratio (>3%) made possible the occurrence of natural nuclear reactors on Earth. These reactors are considered to be a good natural analogue for nuclear waste disposal. Their preservation during such a long period of time is mainly due to the geological stability of the site, the occurrence of clays surrounding the reactors and acting as an impermeable shield, and the occurrence of organic matter that maintained the environment in reducing conditions, favourable for the stability of uraninite. Hydrogeochemical studies and modelling have shown the complexity of the geochemical system at Oklo and Bangombé (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. To cite this article: F. Gauthier-Lafaye, C. R. Physique 3 (2002) 839–849.     

Eco-friendly methods of synthesis and preliminary biological evaluation of sulfonamide derivatives of cyclic arylguanidines

The chemotype of arylsulfonamide derivatives of cyclic arylguanidines is a source of molecules with valuable biological activities, including antimicrobial and antitumor properties. The methods of the synthesis presented in the literature are characterized with low selectivity and high environmental nuisance. In this publication, we present a developed alternative and earlier undescribed pathway C, for the synthesis of arylsulfonamide derivatives of cyclic arylguanidines (N-(1H-arylimidazol-2-yl)arylsulfonamides and N-(1,4-dihydroquinazolin-2-yl)arylsulfonamides), including reaction between 2-(methylsulfanyl)-benzimidazole or 2-(methylsulfanyl)-3,4-dihydroquinazoline with arylsulfonamides. We also optimized previously reported methods; A (reaction of 2-aminobenzimidazole or 2-amino-3,4-dihydroquinazoline with arylsulfonyl chlorides) and B (reaction of dimethyl-(arylsulfonyl)carbonodithioimidate with aryldiamines). The conducted research allowed achieving two independent ecological and quick methods of obtaining the desired products. We used ecological methods of ultrasound-assisted or microwave synthesis, solvent-free reactions and a “green” reaction environment. In both pathways, it has proven advantageous to use H₂O as the solvent and K₂CO₃ (1 or 3 equivalent) as the basic agent. In the sonochemical variant, the efficiency reached B: 37–89 %, C: 90 % in 60 min (P = 80 W and f = 40 kHz), while in the microwave synthesis it was B: 38–74 %, C: 63–85 % in 0.5–4 min (P = 50 W). Path A led to a complementary substitution product (i.e. 1-(arylsulfonyl)-1H-benzimidazol-2-amine or 1-(arylsulfonyl)-1,4-dihydroquinazolin-2-amine). We obtained a small group of compounds that were tested for cytotoxicity. The 10f (N-(1,4-dihydroquinazolin-2-yl)naphthalene-1-sulfonamide) showed cytotoxic activity towards human astrocytoma cell line 1321 N1. The calculated IC₅₀ value was 8.22 µM at 24 h timepoint (doxorubicin suppressed 1321 N1 cell viability with IC₅₀ of 1.1 µM). The viability of the cells exposed to 10f for 24 h dropped to 48.0 % compared to vehicle control, while the cells treated with doxorubicin experienced decline to 47.5 %. We assessed its potential usefulness in pharmacotherapy in the ADMET study, confirming its ability to cross the blood–brain barrier (Pe = 5.0 ± 1.5 × 10^-6 cm/s) and the safety of its potential use in terms of DDI and hepatotoxicity.     

Radionuclides retention: from macroscopic to microscopic

In order to determine the radionuclides' sorption constants on solid natural minerals, both thermodynamic and structural investigations, using spectroscopic techniques, are presented. The natural clays, that could be used as engineering barriers in the nuclear waste geological repository, are rather complex minerals. Therefore, in order to understand how these natural materials retain the radionuclides, it is necessary first to perform these studies on simple substrates such as single crystal, oxides and silicates, and then extrapolate the obtained results on the natural minerals. We examine in this paper the sorption processes of the hexavalent uranium on zircon (ZrSiO₄) and the trivalent curium on a natural clay (bentonite). The corresponding sorption curves are simulated using the results obtained with the following spectroscopic techniques: laser induced spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (EXAFS), diffuse reflectance infrared Fourier transform (DRIFT). To cite this article: E. Simoni, C. R. Physique 3 (2002) 987–997.     

Sonochemical synthesis of two nanostructured silver(I) coordination polymers based on semi-rigid bis(benzimidazole) ligands

Nanoparticles of two silver(I) coordination polymers (CPs), [Ag₂(L1)₂(DCTP)]_n (1) and [Ag₂(L2)(DCTP)]_n (2) (L1 = 1,3-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, L2 = 1,4-bis(benzimidazol-1-yl)-2-butene, H₂DCTP = 2,5-dichloroterephthalic acid), were synthesized by the sonochemical approach and hydrothermal method. Both CPs were characterized by elemental analysis, IR spectra, single-crystal X-ray diffraction, scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). CP 1 exhibits a 2D 4-connected sql net with the point symbol {4⁴.6²}. While CP 2 displays a 2D 3,4-connected 3,4L13 net with the point symbol {4.6²}₂{4².6².8²}. The structural diversity indicates that semi-rigid bis(benzimidazole) co-ligands play important roles in tuning the structures of the mixed Ag(I) CPs. The ultrasound irradiation time, temperature, and power showed significant effects on the morphology and growth process of the nanoparticles of two silver(I) CPs. The luminescence and photocatalytic properties of the nanoparticles of CPs 1–2 on the degradation of methyl blue (MB) were also investigated in detail.     

The τ lepton as a laboratory for quantum chromodynamics

Decays of the τ lepton provide a clean environment to study hadron dynamics in an energy regime dominated by resonances. Inclusive spectral functions are the basis for quantum chromodynamics (QCD) analyses, providing a most accurate determination of the strong coupling constant and quantitative information on nonperturbative contributions. The τ vector spectral function is used together with e⁺e⁻ data in order to compute vacuum polarization integrals arising in the calculations of the anomalous magnetic moment of the muon and the running of the electromagnetic coupling constant. To cite this article: M. Davier, A. Höcker, C. R. Physique 3 (2002) 1223–1233.     

The characteristics of the Opalinus Clay investigated in the Mont Terri underground rock laboratory in Switzerland

In the Mont Terri Rock Laboratory, eleven organisations from six countries (ANDRA and IPSN from France) are investigating jointly a Mesozoic shale formation, the Opalinus Clay. The aims of the research programme are to analyse its hydrogeological, geochemical and rock mechanical properties, the changes induced by the excavation of galleries, by heat-generating waste and by engineered barriers, and to evaluate and improve appropriate investigation techniques. The results of a series of experiments indicate that, at a convenient site, the investigated or similar clay formations could be favourable for hosting a safe repository for radioactive waste. To cite this article: M. Thury, C. R. Physique 3 (2002) 923–933.     

Optical absorption and track studies of gamma-irradiated ZnP glass

The optical absorption spectra of a specially prepared zinc phosphate glass (ZnP) were studied as a function of gamma dose. The optical absorption spectra in the wavelength region of 200–800 nm were recorded for pristine ZnP glass sample and a number of samples exposed to different γ-doses in the range 10⁰–10⁶ Gy. The optical energy gap (E_g) was determined using Tauc's plot. It was found to be independent of γ-irradiation up to the dose of 10³ Gy followed by a slow decrease of E_g up to 10⁵ Gy. However, a sharp decrease in optical energy band gap was observed at 10⁶ Gy. The bulk-etch rates for different γ-doses were also determined and found to be constant up to the dose of 10⁵ Gy. On the other hand, there is a 12% increase in the bulk-etch rate for the dose of 10⁶ Gy.     

Structural changes in ab-plane of Zn doped Bi-2212 HTSC single crystals

Single crystals of undoped and 1% Zn-doped Bi-2212 are grown by self-flux slow cooling method under similar growth conditions. T_c(ΔT_c) are found to be 84 K (2 K) and 82 K (8 K) for undoped and doped samples respectively. Effect of Zn doping on structure and modulation is studied. Different change in the value of a- and b-axes are observed resulting in a transformation of structure from tetragonal to orthorhombic one. However, no effective change in modulation is there. Distortions are compared in c- and b-axes for undoped and doped samples. The asymmetry in position and intensity of satellite peaks has been discussed. The value of a in excess of b has been reported for the first time. These results are discussed in terms of valancy, coordinates and position of occupancy of Zn ions vis-à-vis those of Cu⁻ ions in Cu–O plane of the structure.     

2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Three kinds of donor–acceptor (D–A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be −5.72, −5.67 and −5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (V_OC) in the range, 0.86–0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high V_OC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (J_SC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC₇₁BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron–hole recombination at the polymer/PC₇₁BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC₇₁BM. The PCBTTPD:PC₇₁BM device showed the best PCE of 3.42% with a V_OC and J_SC of 0.86 V and 7.79 mA cm⁻², respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high V_OC and sufficient energy offset for ensuring efficient hole transfer from PC₇₁BM to the polymer.     

Structural,optical and electrical properties of CuSCN nano-powders doped with Li for optoelectronic applications

Pure and Li-doped CuSCN nano-powders were prepared using an in situ method. Structural, optical and electrical properties of the prepared samples were investigated using X-ray diffraction (XRD), UV–Visible spectrophotometer and simple electrical circuit. XRD measurements showed that all pure and doped samples with 1%–7% Li have the hexagonal structures. The crystallite size of CuSCN decreased from 39.46 nm to 36.42 nm with increasing Li concentration from 0 to 7%. The values of direct and indirect optical band gap energies of pure and Li-doped CuSCN nano-powders were calculated. Direct optical band gap energy increased from 3.60 eV to 4.20 eV and indirect optical band gap energy increased from 2.36 eV to 3.20 eV by doping CuSCN with Li. The dc electrical conductivity was calculated at room temperature for all prepared CuSCN samples. Electrical conductivity decreased from 6.04 × 10⁻⁸ (Ω.cm)⁻¹ to 2.82 × 10⁻⁸ (Ω.cm)⁻¹ with increasing Li concentration from 0 to 7%. The optoelectronic performance of CuSCN was improved by doping with Li. As a result, Li-doped CuSCN could be a good candidate material as a window layer and as a hole transport layer (HTL) for producing more efficient solar cells.     

Extended line positions,intensities, empirical lower state energies and quantum assignments of NH3 from 6300 to 7000 cm−1

Nearly 4800 features of ammonia between 6300 and 7000 cm^?1 with intensities ≥4×10^?24 cm^?1/(molecule·cm^?2) at 296 K were measured using 16 pure NH₃ spectra recorded at various temperatures (296–185 K) with the McMath–Pierce Fourier Transform Spectrometer at Kitt Peak National Observatory, AZ. The line positions and intensities were retrieved by fitting individual spectra based on a Voigt line shape profile and then averaging the values to form the experimental linelist. The integrated intensity of the region was 4.68×10^?19 cm^?1/(molecule·cm^?2) at 296 K. Empirical lower state energies were also estimated for 3567 absorption line features using line intensities retrieved from 10 spectra recorded at gas temperature between 185 and 233 K. Finally, using Ground State Combination Differences (GSCDs) and the empirical lower state energy estimates, the quantum assignments were determined for 1096 transitions in the room temperature linelist, along with empirical upper state energies for 434 levels. The assignments correspond to seven vibrational states, as confirmed from recent ab initio calculations. The resulting composite database of ¹⁴NH₃ line parameters will provide experimental constraints to ab initio calculations and support remote sensing of gaseous bodies including the atmospheres of Earth, (exo)planets, brown dwarfs, and other astrophysical environments.     

Investigation of environmental contamination in lichens of Gökçeada (Imbroz) Island in Turkey

The main objective of the present study is to determine the type of environmental contamination in lichens in Gökçeada Island in the Northern Aegean Sea in Turkey. We used two different lichen species Cladonia foliacea and Ramalina pollinaria. In the first part of the investigation, the beta activities of lichens have been measured by using a TENNELEC LB 1000-PW detector.The range of beta activity values was between 607 ± 30 and 308 ± 12 Bq/kg for C. foliacea lichens collected from around Tuz Lake and values for R. pollinaria lichens were found to be 740 ± 25 and 541 ± 17 Bq/kg.The second part of the study was concerned with the gamma spectra of the lichen samples measured by using HpGe detector. ¹³⁷Cs, ¹³⁴Cs, ⁴⁰K, ²³²Th, ²²⁶Ra radionuclides were found in C. foliacea collected from around Tepeköy and in R. pollinaria from around Tuz Lake. When these two types of lichens were compared, it was found that R. pollinaria contain more radionuclides.In order to compare and determine which of these lichens act as a better bioaccumulator, K, Mn, Zn, Rb, Sr, Ba and Pb metal content were determined by using Energy Dispersive X-ray fluorescence spectrometry. It was found that C. foliacea collected more Mn and Sr when compared to R. pollinaria.     

Trapping of metastable high-spin species and weak cooperativity in a mononuclear Fe(II) spin-crossover system

The magnetic and structural properties of three gradual spin transition monomeric compounds based on the cation [Fe(Hpt)₃]²⁺ (Hpt=3-(pyrid-2-yl)-1,2,4-triazole) are presented. The non-cooperative character of the spin-crossover in [Fe(Hpt)₃](BF₄)₂·2H₂O (I) is evaluated in light of its calorimetric properties, which yielded the thermodynamic values Δ_trsH=5.81 kJ mol⁻¹ and Δ_trsS=39.5 J mol⁻¹ K⁻¹. The light-induced excited spin-state trapping effect is performed on [Fe(Hpt)₃](BF₄)₂·2H₂O (I) and [Fe(Hpt)₃](SO₄)_0.4(BF₄)_1.2·3H₂O (II), and the subsequent HS→LS relaxations are studied. Their merely first-order kinetics are affected by disorder in the structure of both complexes, which appears in the presence of a distribution of activation energies. HS species can also be frozen-in in I by rapid cooling. Continuous irradiation is shown to induce only apparent light-induced thermal hysteresis effect in I and II, stemming from slow kinetics of relaxation with respect to the kinetics of measurement.