Релятивистским методом дискретного варьирования выполнен расчет электронного строения NoO2 и спектра РФЭС (рентгеновской фотоэлектронной спектроскопии) валентных электронов в диапазоне энергий связи от 0 до ~40 эВ. Наблюдаются значительные эффекты ковалентности в NoO2, обусловленные существенным перекрыванием не только No 6d АО, но и No 6p и No 5f АО с орбиталями кислорода. Построены гистограмма и схема МО, позволяющие понять особенности природы химической связи и структуру спектра РФЭС валентных электронов в NoO2.

The electronic structure of NoO2 and the valence-band X-ray photoelectron spectrum (XPS) in the energy range from 0 eV to 40 eV are calculated by the relativistic discrete variation method. Significant covalency effects are observed in NoO2, which are due to a considerable overlap of not only No 6d AO but also No 6p and No 5f AOs with oxygen orbitals. The MO histogram and scheme are derived, which enable the comprehension of features of the chemical bond nature and the structure of the XPS spectrum of valence electrons in NoO2.

The electronic structure of AnO2 (An = Th‒Lr) and the structure of X-ray photoelectron spectra of their valence electrons were calculated by the relativistic discrete variation method in the MO LCAO cluster approximation (molecular orbitals as linear combinations of atomic orbitals). This structure is in satisfactory agreement with the available experimental spectra. The effective charges QAn of the An ions in AnO2 were determined as the difference between the number of electrons in the neutral An atom and the number of electrons in the actinide ion in the AnO8 cluster. The dependence of the effective charges QAn in AnO2 on the atomic number Z was obtained. The estimated values in the range 0.42 e < QAn < 1.04 e differ significantly from QAn(IV) = 4 e, found in the ionic approximation. This is attributed to the significant covalence effects in AnO2, associated with the overlap of not only An6d, but also of An6p and An5f AOs with the oxygen orbitals. There is qualitative agreement between the obtained QAn values and the values of the chemical shifts (several electron-volts) of the lines of the actinide 4f core electrons in the XP spectra of dioxides relative to the metals.

The ionic composition of ferrogranate powder samples of composition Y2.5Ce0.5Fe2.5Ga2.5O12 obtained by gel combustion followed by crystallization at 750°С in a furnace for 5 h at a pressure of ≈ 1 × 10–2 Pa has been studied by XANES method. The results are compared with the X-ray powder diffraction and X-ray photoelectron spectroscopy (XPS) data obtained by the authors earlier. It is shown that according to X-ray powder diffraction data, ferrogranate Y2.5Ce0.5Fe2.5Ga2.5O12 is single-phase, but according to the results of XANES and XPS, spectroscopy along with Ce3+ in the sample Ce4+ is present both in the volume and on the surface of crystallites.

Релятивистским методом дискретного варьирования (РДВ) рассчитана плотность состояний валентных электронов диоксида EsO2. Построена схема молекулярных орбиталей (МО) валентных электронов и с учетом сечений фотоэффекта валентных электронов построена гистограмма спектра РФЭС (рентгеновской фотоэлектронной спектроскопии) в диапазоне энергий связи электронов от 0 до ~40 эВ. Показано, что в структуру этого спектра вносят вклад электроны внешних валентных (ВМО, от 0 до ~15 эВ) и внутренних валентных (ВВМО, от ~15 до ~50 эВ) МО. Установлено участие Es 5f- и Es 6p-электронов в химической связи. Наблюдается значительное перекрывание не только Es 6d АО, но и Es 6p и Es 5f АО с орбиталями лигандов, что обусловливает высокий вклад ковалентной составляющей в химическую связь в этом диоксиде. Отмечается, что схема МО позволяет понять природу химической связи и структуру спектра РФЭС валентных электронов в EsO2. Показано, что электроны ВВМО на треть ослабляют химическую связь, обусловленную электронами ВМО.

The density of states of valence electrons of the EsO 2 dioxide is calculated by the relativistic discrete variational method. The scheme of valence molecular orbitals (MOs) is constructed taking into account the photoelectric effect cross sections of valence electrons. The histogram of X-ray photoelectron spectra (XPS) is built for the electron binding energies from 0 eV to ~40 eV. It is shown that the structure of this spectrum contains contributions of outer valence orbitals (OVMOs, from 0 eV to ~15 eV) and inner valence orbitals (IVMOs, from ~15 eV to ~50 eV) molecular orbitals. It is established that Es 5 f and Es 6 p electrons participate in the chemical bonding. It is established that not only Es 6 d , but also Es 6 p and Es 5 f orbitals overlap significantly with ligand orbitals, resulting in a highly covalent chemical bonding in this dioxide. The nature of chemical bonding and the structure of the XPS spectrum of valence electrons in EsO 2 is clarified using the scheme of MOs. It is shown that the chemical bonding formed by OVMO electrons is weaken by one third due to IVMO electrons.

The complex structure of precision X-ray photoelectron spectra (XPS) of valence and core electrons of a ThO2(001) crystal film on Si(100) was obtained and analyzed, and the electronic structure of ThO8, Th13O56, and Th63O216 clusters was calculated. A histogram of the calculated XPS spectrum of electrons of the outer (from 0 to ~15 eV, OVMO) and inner (from ~15 to ~35 eV, IVMO) valence MOs was plotted. The calculated spectrum was in good agreement with the experimental one. Significant overlap of Th 6d atomic orbitals (AO) as well as Th 6p, 5f AO with oxygen orbitals is noted, which brings about the covalent nature of the bond in this dioxide. The contribution of the OVMO and IVMO electrons to the chemical bond was estimated based on the values of the bond populations. It was shown that the IVMO electrons weaken the chemical bond caused by OVMO electrons. It is assumed that the complex structure in the spectra of the Th 5s and Th 5p electrons is largely due to the dynamic effect, which does not allow observing the structure in the spectrum of the Th 5s electrons in ThO2.

The relativistic method of discrete variation has been used to calculate the density of states and the X-ray photoelectron spectroscopy spectrum of valence electrons in the range of electron binding energies from 0 to ~50 eV in PaO2. A scheme of molecular orbitals has been constructed. Significant covalence effects are observed in PaO2, which are associated with the overlap of not only Pa6d atomic orbitals but also Pa6p and Pa5f atomic orbitals with oxygen orbitals. It has been found that the electrons of the inner valence molecular orbitals weaken the chemical bond formed by the electrons of the outer valence molecular orbitals.

In the approximation of the relativistic discrete variation method, the valence X-ray photoelectron spectrum of CmO2 was calculated, and satisfactory agreement with the structure of the experimental spectrum was found. It was shown that the structure of the spectrum is due to the electrons of the outer (from 0 to ~15 eV) and inner (from ~15 to ~35 eV) valence molecular orbitals, which leads to an increase in the covalency of the chemical bond in CmO2. The effective charge of curium in CmO2 was determined, and the contribution of various electrons to the chemical bond was evaluated. A semiempirical scheme of molecular orbitals for CmO2 was constructed.

The first calculations of the electronic structure and X-ray photoelectron spectrum (XPS) of valence electrons of BkO2 in the 0 to ~50 eV range of binding energies are made via relativistic discrete-variational method (RDV). Satisfactory agreement is established between the calculated and experimental spectra of this dioxide, obtained in the works of other authors. A quantitative molecular orbitals (MO) scheme is constructed that allows us to understand the nature of the chemical bonds and the structure of the XPS of valence electrons in BkO2. In contrast to the concepts of the crystal field theory, the effects of covalence in BkO2 are considerable and result in strong overlapping not only of the Bk6d, but of Bk6p, 5f atomic orbitals (AO) with ligand orbitals as well. It is found that the electrons of inner valence molecular orbitals (IVMO) weaken the chemical bonds caused by the electrons of outer valence molecular orbitals (OVMO) by 28%.

Проведен расчет электронной структуры CfO2 в полностью релятивистском кластерном приближении метода дискретного варьирования (РДВ). Получен теоретический спектр рентгеновский фотоэлектронный спектроскопии (РФЭС) валентных электронов в диапазоне энергий связи электронов 0…~40 эВ. Показано, что в образовании внешних валентных молекулярных орбиталей в диапазоне энергий 0…~15 эВ принимают участие атомные орбитали Cf 5f и Cf 6p. Основной вклад в образование внутренних валентных молекулярных орбиталей в диапазоне энергий ~15…~40 эВ вносят АО Cf 6p3/2 и O 2s. Значительные эффекты ковалентности в CfO2 связаны с сильным перекрыванием АО с орбиталями лигандов не только Cf 6d, но и Cf 5f, а также Cf 6p. Структура МО с участием АО Cf 6d, 7s и 7р мало меняется по сравнению с таковой диоксидов более легких актиноидов. Эти МО вместе с содержащими O 2s и О 2р АО образуют «жесткий каркас», в котором перемещаются МО, включающие An 5f АО. Построена теоретическая схема МО, позволяющая понять природу химической связи и структуру спектра РФЭС валентных электронов в CfO2.