Hydrogen Complexes Research Articles

Investigation of the hydrogen, halogen and pnicogen dimers by means of molecular face calculated by ab initio method

The noncovalent interactions, including hydrogen, halogen and pnicogen bonds, are widely known due to their significant role in both chemical reactions and biological phenomena. In this work, the potential acting on an electron in a molecule (PAEM) is introduced to present the strength and regioselectivity of noncovalent interaction. The PAEM height of noncovalent bonds, Dpb, can characterize the strength of the interaction, which has the linear relationships with noncovalent binding distances and binding energies. Here, we employ the molecular face theory (MFT) based on the PAEM to visualize reactive sites for the monomers in noncolvalent bond complexes. The electron density extremes on the molecular face (MF) regarded as the local reactivity descriptor are applied to exhibit the regioselectivity and preferred direction for monomers in hydrogen, halogen and pnicogen binding complexes, in good agreement with the chemical convention and ab initio calculation results. And the overlap distances of MF between dimers have been proposed and obtained to evaluate the strength of noncovalent interaction. The MFT provides a new way to demonstrate the regioselectivity and can be applied to larger and other type molecules in the future.

Integrating Effect of Surface Modification of Microporous Carbon by Phosphorus/Oxygen as well as the Redox Additive of p‐Aminophenol for High‐Performance Supercapacitors

AbstractIn present work, commercial microporous carbon materials are modified on the surface with phosphorus/oxygen species by using phytic acid as sole dopant, which plays crucial effect on the carbon structure, wettability, electrical conductivity, and capacitive behaviors. It reveals that with increasing the content of heteroatoms, the porosity and contact angle are decreased but the conductivity turns much larger. Furthermore, p‐aminophenol is introduced to serve as redox additive, which can produce more active surface sites by forming hydrogen bond and complexation with the surface functional groups, further providing additional pseudo‐capacitance. As a result, the energy density of carbon sample by phosphorus/oxygen doping in 1 m H2SO4 electrolyte with p‐aminophenol is as high as 9.2 Wh kg−1, which is 2.6 than that of pristine carbon. What is more, in terms of the simple operation and effective performance, the integration of surface modification toward carbon materials and redox additive can be favorable for largely enhancing the supercapacitor performance.

General Explicit Mathematical Solution for the Voltammetry of Nonunity Stoichiometry Electrode Reactions: Diagnosis Criteria in Cyclic Voltammetry.

Electrochemical reactions can effectively follow nonunity stoichiometries as can be found in the electrochemistry of halides, hydrogen, and metal complexes. The voltammetric response of these systems shows peculiar deviations with respect to the well-described features of the 1:1 stoichiometry. With the aim of specifying such differences, a rigorous and manageable analytical theory is deduced for the complete characterization of reversible electrode processes with complex stoichiometry in cyclic voltammetry (CV) at macroelectrodes. Particularly, the main features of the CV of 2:1, 1:2, 3:1, and 1:3 processes (that is, the peak currents and potentials and the influence of the scan rate and of the species concentration and diffusion coefficients) are given and compared with the 1:1 case in order to propose unambiguous diagnostic criteria of the stoichiometry of the electrode reaction. Also, expressions for the concentration profiles and surface concentrations of the redox species are given.

DFT исследование триплетных и синглетных элементарных актов окисления ациклических и циклических алканов, инициированных первичным взаимодействием с 3O2

The primary oxidation stages of 3O2 model acyclic and cyclic alkanes and their subsequent triplet and singlet elementary events were studied for the first time by the DFT method with the density functional B3LYP and basis set 6-311++g(df,p). According to quantum chemical DFT calculations the C–H radical cleavage of the bonds of acyclic and cyclic alkanes upon interaction with 3O2 is almost completely thermodynamically shifted toward the initial state of the reaction system. This energy of primary oxidizing events explains the extremely low reactivity of saturated alkanes in comparison with asphaltene structural fragments under the conditions of SCF technology for the extraction of heavy oils and asphaltenes by a propane-butane mixture. It has been demonstrated that for all elementary acts of primary alkane oxidation the product of the direct reaction direction is not a free pair of radicals but a triplet hydrogen complex with a pronounced hydrogen bond between the hydroperoxyl radical and the radical form of the corresponding hydrocarbon. A new, previously not taken into account very exothermic (H = -29.25 – -30.77 kcal/mol) reaction direction is described which corresponds to triplet recombination of alkyl radicals and a hydroperoxyl radical in its oxygen-concentrated part. The products of this recombination are triplet forms of alkane hydroperoxides in which there is a fairly loosened triplet O---O bond with a length of 2.20-2.23 Å, which is ~0.72-0.77 Å more than bond length in the singlet state.

Molecular Dynamics Simulation of the Implantation of b-Oriented ZSM-5 Film Modified α-Quartz Substrate Surface With Different Modifiers.

In this study, we investigated the structure–absorption relationship of common surface modifiers of chitosan (CTS), polyvinyl acetate (PVA), and titanium dioxide (TiO2) with α-quartz surface using molecular dynamics simulation. And the orientations and combinations derived from structures between modified α-quartz and ZSM-5 crystallites were also investigated. The results show that PVA is a non-linear organic macromolecule with a large amount of hydroxyl groups on its surface, which easily adhere to the surface of the substrate and agglomerate. CTS is a straight-chain structure containing a large number of hydroxyl and amino groups, which easily accumulate and spread on the surface of the substrate. TiO2 not only forms hydrogen bonds and complexes with the substrate but also interacts with each other to form a dense modifier layer. We observed that a large number of stable Ti–O–Si chemical bonds formed between the modified layer of inorganic small-molecule TiO2 and the surface of α-quartz, which compacted and stabilized the attached ZSM-5 film. Moreover, the orientation angle of the ZSM-5 nanocrystalline nucleus on the modified α-quartz was computed, which confirmed that the b-axis orientation of the ZSM-5 nanocrystalline nucleus was the highest on the surface of the substrate modified by TiO2. We discussed the influence of the modified temperature of modifiers in the constructed materials, and we have observed the adsorption state differences of TiO2 at different modified temperatures. We also discussed the catalytic properties of the materials prepared by the corresponding methods in conversion of methanol-to-aromatics (MTA) reaction. These results agree with our previous experimental data. By employing molecular dynamics simulation, we have obtained more precise conclusive information of the b-oriented growth of ZSM-5 crystallites, which highly depends on the surface modifiers.

Complexes of Alkali Metal Cations and Molecular Hydrogen: Potential Energy Surfaces and Bound States.

Complexes between metal cations and molecular hydrogen are systems quite amenable for precise spectroscopic and theoretical studies, and at the same time, they are relevant for applications in hydrogen storage and astrochemistry. In this work, we report new intermolecular potential energy surfaces and rovibrational states calculations for complexes involving molecular hydrogen and alkaline metal cations, M+-H2 (M+ = Na+, K+, Rb+, Cs+). The intermolecular potentials, formulated in an internally consistent way to emphasize differences in the properties of the systems, are represented by simple analytical expressions whose parameters have been optimized from comparison with accurate ab initio calculations. Properties of the low-lying bound states-binding energies, frequencies, and rotational constants-are compared with previous measurements or computations and an overall good agreement is achieved, supporting the reliability of the present formulation. Variations of these properties as a function of the cation size and isotopic substitution, with a proper sequence of ortho and para rotational levels, are also discussed.

The Molecular Basis for Understanding the Impacts of Ocean Warming

AbstractA grand challenge for ocean chemists in the years ahead lies in the need to tackle the chemical consequences of ocean warming with the same rigor and intensity that has been brought to bear on the physical chemistry of ocean acidification. For over 50 years ocean chemistry has been dominated by the study of pH‐dependent processes, but to address the biogeochemical impacts of ocean warming, we will need to rapidly advance the discipline of ocean chemical physics where temperature is the master variable and the basic unit is the Joule. Just as it would be impossible to understand the ocean CO2 system without awareness of the essential pH‐dependent CO2‐HCO3‐CO3 equilibria, so too is it impossible to describe ocean chemical physics without knowledge of the bimolecular structure of water. Water, and water in sea water, is composed of a complex of dominant hydrogen bonded forms, and the singlet molecular H2O species, in temperature‐controlled equilibrium and the ratio of these forms, can now be precisely determined. The physical properties of sea water are traditionally described by fitting an ad hoc collection of coefficients to experimental data. They are more accurately described as temperature and pressure perturbations of the underlying molecular equilibrium state. Ocean oxygen consumption rates are accurately described as an Arrhenius function, and not as an exponential function of depth as has been the tradition for over 50 years. We do not now have good correlation between ocean models and observed warming and oxygen declines, and full anoxia with the emergence of hydrogen sulfide over large regions of the ocean is possible. The parallel ocean invasions of heat and fossil fuel CO2 must be combined to estimate their full impact.

Evaluation of System Effectiveness of Multifunctional Hydrogen Complex at Nuclear Power Plants

The paper gives the analysis of the problem of the primary current frequency regulation in the power system, as well as the basic requirements for NPP power units under the conditions of involvement in the primary regulation. According to these requirements, the operation of NPPs is associated with unloading and a corresponding decrease in efficiency. In this regard, the combination of nuclear power plants with a hydrogen complex is shown to eliminate the inefficient discharge mode which allows the steam turbine equipment and equipment of the reactor facility to operate in the basic mode at the nominal power level. In addition, conditions are created for the generation and accumulation of hydrogen and oxygen during the day, as well as additionally during the nighttime failure of the electrical load which allows them to be used to generate peak power. The purpose of the article is to assess the systemic economic effect as a result of the participation of nuclear power plants in combination with the hydrogen complex in the primary control of the current frequency in the power sys-tem, taking into account the resource costs of the main equipment. In this regard, the paper gives the justification of cyclic loading of the main equipment of the hydrogen complex: metal storage tanks of hydrogen and oxygen, compressor units, hydrogen-oxygen combustion chamber of vapor-hydrogen overheating of the working fluid in the steam turbine cycle of a nuclear power plant. The methodological foundations for evaluating the working life of equipment under cyclic loading with the participation in the primary frequency control by the criterion of the growth rate of a fatigue crack are described. For the equipment of the hydrogen complex, the highest intensity of loading is shown to occur in the hydrogen-oxygen combustion chamber due to high thermal stresses. The system economic effect is estimated and the effect of wear of the main equipment under cyclic loading is shown. Under the conditions of combining NPP power units with a hydrogen complex, the efficiency of primary reg-ulation is shown to depend significantly on: the cost of equipment subjected to cyclic loading; frequency and intensity of cyclic loading; the ratio of the tariff for peak electricity, and the cost of electricity of nuclear power plants. Based on the developed methodology for assessing the effectiveness of the participation of nuclear power plants with a hydrogen complex in the primary frequency control, taking into account the damage to the equipment, the use of the hydrogen complex is shown to provide a tangible economic effect compared with the option of unloading nuclear power plants with direct participation in frequency control.

Predicted Economic Efficiency of Combining NPPS with an Autonomous Hydrogen Energy Complex

Currently, the Unified Energy System of Russia has a tendency to increase the deficit of peak and semi-peak capacities with a simultaneous increase in the number of NPP which requires the participation of NPPs in a variable part of the schedule electrical loads. In addition to the economic need to maintain the installed capacity utilization rate at a high level, there are technological limitations for maneuvering characteristics for NPPs. The authors have developed an approach to solving this problem based on combining with an environmentally friendly energy source – an autonomous hydrogen complex which includes heat accumulators and an additional multifunctional low-power steam turbine installation. The developed power complex can also provide reliable redundancy of power supply of NPP own needs in the event of a total station blackout. The paper carries out the evaluation of the technical and economic parameters of the main equipment of the autonomous hydrogen complex required for combination with a two-unit NPP with a VVER-1000. Based on the assessment of inflation indicators of the Russian economy over the past 11 years, three options have been identified for fuel cost and tariff rates for electricity (capacity), as well as the size of operating costs, including depreciation in the main equipment, taking into account current pricing principles. As a result, the values of accumulated net present value were obtained depending on the ratio of the cost of semi-peak and non-peak electricity tariffs at different inflation rates. We have taken into account the positive economic effect of reducing the risk of damage to the reactor core, replacing the construction of gas turbines as a maneuverable source of electricity in the power system, and increasing the income of the federal budget of the Russian Federation from saving natural gas. The economic conditions of competitiveness of the proposed approach to improving the maneuverability and safety of NPP are determined. The highest economic efficiency is achieved with the maximum projected inflation which is associated with the maximum discount rate and high rate of growth of electricity tariffs. Reducing the risk of damage to the core allows us to provide the competitiveness of the proposed approach in all considered variants of inflation and the ratio of electricity tariffs.

Temperature dependence of vacancy concentration and void growth mechanism in Al with constant hydrogen concentration: A first-principles study

In this study, a formulation that yields the chemical potential of solute hydrogen and thermal equilibrium concentrations of various coexisting vacancies, including atomic vacancy and vacancy–hydrogen complexes under the conditions of constant solute hydrogen concentration and temperature, is first proposed. The chemical potential of solute hydrogen and vacancy concentrations in Al are then obtained by evaluating the temperature-dependent physical properties in the equations via density functional theory and lattice vibration analyses. We found that hydrogen disbanded from vacancy–hydrogen complexes to form empty vacancy and interstitial hydrogen at the critical temperature approximately 200–300 K, depending on the solute hydrogen concentration. Finally, we revealed the operation temperatures of two principal void growth mechanisms by using the hydrogen pressure in the voids that are estimated from the chemical potential of hydrogen, vacancy concentrations, and diffusion coefficient of atomic vacancy. The first mechanism is plastic deformation growth, which is caused by high pressure inside the void at lower temperature. The other one is vacancy absorption growth mechanism, which is caused by absorbing diffusive vacancy in the lattice at higher temperature.

Effects of various types of hydrogen dopants on optical properties of ZnO

An investigation was carried out to study the effects of various types of hydrogen dopants including, substitutional H on oxygen site (HO), interstitial hydrogen (Hi), and oxygen vacancy plus interstitial hydrogen (VO+Hi) complex on optical properties of ZnO using GGA and GGA + U calculations. It can be shown by our studies that GGA approximation is convenient for structural and charge density calculations but it is not sufficient in calculating both the formation energy and interband energy levels. Therefore, we calculated optical properties using both of GGA + scissor shift, and GGA + U calculations (for VO+Hi doping). Optical calculations revealed that due to the hydrogen incorporation, the optical band gap of ZnO increases while this increment is small in Hi and more pronounced in HO. In addition, the HO doped ZnO causes an increment in optical transmission in the visible region and a significant improvement in the UV region. So, it is appropriate for the transparent conducting oxide (TCO) layers and UV applications. Whereas the VO+Hi defect decreases the optical band gap of ZnO to about 1.2 eV, it strongly increases absorption and reflectivity coefficient of ZnO in the visible region. Therefore, it can be used in applications such as photocatalysts, solar cells, and photoelectrochemistry.

Intermolecular complexes of halocyclopropenone derivatives with the hypohalousacids HOF, HOCl, HOBr, and HOI

The intermolecular interactions between halocyclopropenone derivatives (HC$_{3}$OX; X $=$ I, Br, Cl, and F) and hypohalous acids (HOY; Y $=$ I, Br, Cl, and F) were studied via the MP2 method utilizing the aug-cc-pVTZ and aug-cc-pVTZ(-PP) basis sets. The three types of complexes were hydrogen bonds, halogen bonds, and complexes containing both hydrogen and halogen bonds. The results obtained indicated that interactions in the Type 1 complexes were stronger than those in Types 2 and 3. The H-O bonds revealed red shifts with complex formation in Types 1 and 2. The O-Y bonds displayed red shifts in the Type 3 and blue shifts in the Type 2 structures. Molecular electrostatic potential, quantum theory of atoms in molecules, and natural bond orbital methodologies were used to analyze these interactions.

In-situ Fe-doped g-C3N4 heterogeneous catalyst via photocatalysis-Fenton reaction with enriched photocatalytic performance for removal of complex wastewater

In this work, an in-situ Fe-doped g-C3N4 catalyst was synthesized by thermal shrinkage polymerization. A heterogeneous photocatalysis-Fenton system was formed with the addition of H2O2 under visible irradiation and exhibited excellent and recyclable removal performance for refractory contaminants such as: phenol, bisphenol A, 2, 4-dichlorophenol and coking wastewater, which was due to the formation of σ-π bonds via Fe and N element in the triazine ring skeleton of Fe-g-C3N4. The electrons generated can be quickly transferred to Fe3+ to form Fe2+ under the interaction of the chemical bond. The efficiency of photoelectron separation was accelerated, and OH radicals were quickly generated with the reaction between Fe2+ and H2O2. Specifically, the recycling of Fe can be achieved in the heterogeneous system, which avoids the problems for the recycling and secondary pollution of Fe ions in homogeneous Fenton reaction. Parameters such as Fe doping amount, hydrogen peroxide concentration, pH value, catalyst concentration, and complex wastewater (coking wastewater) were optimized. The degradation of coking wastewater were also performed, and the chemical oxygen demand (COD) and total organic carbon (TOC) values for 300 ml coking wastewater could be reduced from 64.6 and 25.3 mg/L to 22.8 and 12.3 mg/L in 60 min, respectively. These results demonstrate photocatalysis-Fenton reaction with Fe-g-C3N4 catalyst is promising for environmental remediation.

Research of the efficiency of combining nuclear power plants with a multifunctional autonomous hydrogen energy complex

Combining of the nuclear power plant power unit with an autonomous hydrogen complex including a low-power steam-turbine is proposed. This autonomous hydrogen complex makes it possible to increase the power and manoeuvring capabilities of the nuclear power unit, and in case of complete power blackout, provide power supply for own needs for more than 72 hours (IAEA requirement) due the energy of the residual heat release of the reactor. Hydrogen and oxygen can be generated by electrolysis of water at the expense of cheap off-peak energy of nuclear power units at night, after that it is effectively used in the daytime to generate steam, which is sent to a low-power steam turbine. The article evaluates the economic efficiency of the proposed system under conditions of uneven electric load schedule. It is shown that the proposed variant of combining nuclear power units with an autonomous hydrogen complex, including a low-power steam-turbine plant, makes it possible to improve the reliability of power supply for NPP’s own needs in emergency situations with blackout. This will, together with the additional benefit from the sale of peak electricity, significantly increase the competitiveness of nuclear power plants.

Adsorption and Diffusion of Hydrogen on Low-Index (110) and (111) Surfaces of Aluminum

By the density-functional method, the authors have considered the energetics of adsorption and diffusion of a hydrogen molecule into atomically thin aluminum plates with body-centered tetragonal and rhombohedral crystallite structures bounded by the (110) and (111) surfaces, and also geometric configurations of surface aluminum hydrides. It has been shown that physical adsorption of H2 molecules on the Al(110) and Al(111) surfaces is a weak exothermic process. Polarization and deformation due to the physical adsorption lead to a certain increase in the H–H interatomic spacing (0.734 A). The diffusion of the hydrogen atoms into body-centered tetragonal and rhombohedral plates tends to increase the system's energy. It has been found that hydrogen diffuses most easily through the Al(110) surface; in atomic diffusion through the subsurface layer, the energy grows up to 1.1 eV. A stable energy state is attained due to the formation of a tetrahedral hydrogen complex.

Effect of interatomic potential on the energetics of hydrogen and helium-vacancy complexes in bulk, or near surfaces of tungsten

Hydrogen (H) trapping by helium-vacancy (HeV) complexes in bulk and the near surface region of tungsten (W) have been investigated by molecular statics calculations that evaluate two different WH interatomic potentials, which use the same WHe, HeHe and HeH potentials. One of the WH potentials is a bond-order potential (BOP) developed by Juslin et al., while the other is an embedding atom method (EAM) potential developed by Wang et al.. Both potentials overestimate the H binding energies to He clusters in bulk W, as compared to DFT calculations, but properly predict the functional form of the H binding energies to He clusters with increasing number of He and H. The BOP simulations reveal that H binding energies to HexV complexes generally increase with increasing number of He. However, the EAM results indicate that the H binding energy as a function of number of He depends on the number of H, and the H binding energies change slightly at high He content. Compared with available DFT data, both BOP and EAM underestimate the H binding energies to HexV2Hm complexes. The BOP reproduces the He formation energy below a W surface, while the EAM potential better reproduces the H formation energy and the interactions between H and HeV complexes. Based on these comparisons, we determine that the EAM potential is more accurate than BOP for large-scale molecular dynamics simulations of WHeH interactions. The EAM potential predicts that the difference in the average binding energies of H to stable HeV complexes near the W surface is less than 0.2 eV and the difference decreases with increasing He content. Thus, the EAM potential indicates that the effect of surfaces on H binding energies to large HeV complexes below the W surfaces can be ignored.

The Effect of a Polar Solvent on the ππ*-Bands of Chlorophenol Isomers

The optical absorption spectra of para-, meta-, and ortho-chlorophenol in the gas phase and in a polar solvent (methanol) are recorded. It is shown that the bathochromic shifts of the first and second ππ* absorption bands in a methanol solution compared to their positions in the gas phase are caused by the formation of a hydrogen bond between chlorophenol and methanol molecules and by the effect of solvent on the formed hydrogen complex. The result was obtained by calculating electronic spectra by the TDDFT B3LYP/6-311++G(d,p) method with the use of the polarizable continuum model.

Mechanism for phosphorus deactivation in silicon-based Schottky diodes submitted to MW-ECR hydrogen plasma

Current work reveals the deactivation mechanism of phosphorus in silicon-based Schottky diodes. Microwave plasma power (PMW) was fixed at 650 W to observe the variation in different operational parameters of diodes such as initial phosphorus concentration, flux and hydrogenation temperature (TH) and process time (tH). The analysis of variation in concentration of phosphorus by hydrogenation has been carried out by capacitance–voltage (C–V) measurements to monitor the doping activation/deactivation. The results clearly show that the atomic species H+ is dominant in the reactors MW-ECR plasma. Therefore, the rates and depth of neutralization were obtained in the low phosphorus-doped silicon sample. The H+ becomes H0 and prefers an interaction with another H0 instead of gaining an electron to become a negative ion. The hydrogenation temperature study indicates that the deactivation rate of phosphorus is achieved in a complex manner. Indeed, as the hydrogenation temperature increases, deactivation of phosphorus also increases till saturation at 250 °C. At higher temperature, low or even no phosphorus–hydrogen complex exists due to their thermal dissociation. The same behavior was confirmed by long hydrogenation.

Internal defect structure of calcium doped magnesium oxide nanoparticles studied by positron annihilation spectroscopy

Calcium-ion substitution to different concentrations in the normally insulating but wide band gap semiconductor magnesium oxide nanocrystallites was successfully achieved through a sol-gel route and the synthesized samples were characterized by X-ray diffraction and transmission electron microscopy. The substitution of Mg2+ by Ca2+ gave rise to distinct variation in the nanocrystallite sizes and lattice constants. The band gap energies (Eg = 5.04 to 5.50 eV) obtained from ultra-violet and visible absorption spectroscopy hinted to the formation of Positronium Hydrogen (Ps-H) complex within nanocrystallites. Excitonic energy levels reduced the band gap after doping. In the samples of larger nanocrystallites, strong evidences to the presence of very large vacancy clusters were observed. The coincidence Doppler broadening measurements also indirectly supported this interpretation. The lineshape and wings parameters also supported the type of defects as evidenced from lifetime measurements. The results appeared significant from the context of choosing doping as an efficient way of molding the properties of semiconductor oxide nanocrystals as concomitant lattice parameter variations and the evolutions of vacancy type defects can significantly alter the expected physical changes towards other directions.

Defect transformations in nitrogen-doped CVD diamond during irradiation and annealing

Nitrogen-doped CVD diamond treated with electron irradiation and subsequent annealing at temperatures from 860 to 1900 °C was studied using fluorescence imaging, optical absorption and photoluminescence. It was found that nitrogen impurity produces many optical centers active throughout the infrared and visible spectral ranges. The most prominent of them active in IR spectral range are the centers related to nitrogen–hydrogen complexes. They produce absorption lines at 2827, 2874, 2906, 2949, 2990, 3031, 3107, 3123 and 3310 cm−1. Two characteristic absorptions at wavenumbers 1293 cm−1 and 1341 cm−1 were tentatively ascribed to a modified form of nitrogen A-aggregates. In the visible and near IR spectral ranges, characteristic nitrogen-related centers have zero-phonon lines (ZPLs) at 457, 462, 489, 498, 722.5, 852.5, 865.5, 868.5, 908, 921.5 and 924.5 nm. Some of them, e.g. 457, 462 and 498 nm centers, are unique of CVD diamond. It has been confirmed that the brightest pink color of electron-irradiated nitrogen-doped CVD diamond is produced by annealing at temperatures about 1000 °C. Annealing at temperatures over 1600 °C destroys the irradiation-induced pink color. It was found that the center 489 nm is a major absorption feature in the visible spectral range of electron-irradiated, nitrogen-doped CVD diamond. Green color of electron-irradiated, nitrogen-doped CVD diamond is caused by combined absorption of GR1 center and 489 nm center. It has been confirmed that NV defects produced in CVD diamond during growth are very temperature stable. They survive heating at temperatures at least 2000 °C. In contrast, NV defects produced by irradiation may anneal out at temperatures as low as 1600 °C. This much lower thermal stability of the radiation-induced NV defects is the result of their interaction with other radiation defects produced in their vicinity. A conclusion has been made that in nitrogen-doped CVD diamonds nitrogen atoms may form clusters. These clusters are probably the origin of the broad band luminescence at wavelengths 360, 390, 535 and 720 nm and a strong broadening of ZPLs of many optical centers.