Флуктуирующая флуоресценция одиночных центров окраски в кристаллах фторида лития

Single F2 and F3+- color centers in the LiF crystal were studied by confocal fluorescence microscopy. The time dependences of their fluorescence intensity were analyzed and statistically processed. Our studies show that, the F3+- color center, being photoexcited, is able enter the triplet state, while in ground (singlet) state it changes orientation with a frequency of 1.5 – 2 Hz at room temperature, due to reorientational diffusion, unlike the F2- center, which is reoriented only being in the triplet state. This subtype of rotational diffusion of the center does not lead to its translational diffusion.

A full dimensional potential for H2O2 (X1A) covering all dissociation channels

A full dimensional potential energy surface for the H2O2 ground singlet state including all the dissociation channels.

Semiempirical modeling of electrochemical charge transfer

Nanoelectrochemical experiments using detection based on tip enhanced Raman spectroscopy (TERS) show a broad distribution of single-molecule formal potentials E°′ for large π-conjugated molecules; theoretical studies are needed to understand the origins of this distribution. In this paper, we present a theoretical approach to determine E°′ for electrochemical reactions involving a single molecule interacting with an electrode represented as a metal nanocluster and apply this method to the Ag20–pyridine system. The theory is based on the semiempirical INDO electronic structure approach, together with the COSMO solvation model and an approach for tuning the Fermi energy, in which the silver atomic orbital energies are varied until the ground singlet state of Ag20–pyridine matches the lowest triplet energy, corresponding to electron transfer from the metal cluster to pyridine. Based on this theory, we find that the variation of E°′ with the structure of the Ag20–pyridine system is only weakly correlated with changes in either the ground-state interaction energy or the charge-transfer excited-state energies at zero applied potential, which shows the importance of calculations that include an applied potential in determining the variation of formal potential with geometry. Factors which determine E°′ include wavefunction overlap for geometries when pyridine is close to the surface, and electrostatics when the molecule-cluster separation is large.

Synthesis, molecular and electronic structure of a stacked half-sandwich dititanium complex incorporating a cyclic π-faced bridging ligand

The thermally robust ground singlet state complex [bis(η5-pentamethylcyclopentadienyltitanium)-μ-(η4:η4-1,2,4,5-tetrakis(trimethylsilyl)cyclohexa-1-4-diene-3,6-diyl)] (3) arises from thermolysis of Cp*TiMe3.

Electronic States and Optical Gap of Phosphorus-Doped Silicon Nanocrystals Embedded in a Silica Host Matrix

Using the envelope-function approximation the electronic states and the optical gap of silicon nanocrystals heavily doped with phosphorus have been calculated. Assuming the uniform impurity distribution over the crystallite volume we have found the fine structure of the electron ground state (induced by the valley-orbit interaction) and the optical gap as a function of the crystallite size and donor concentration. It is shown that the energy of the ground singlet state decreases almost linearly as the concentration increases, while the valley-orbit splitting increases nonlinearly. Phosphorus doping also results in the decrease of the nanocrystal gap with increasing the impurity concentration.

Low-lying activated states of chloroiridium phthalocyanine aggregates in glassy solution at low temperatures

Studies of phosphorescence intensities and lifetimes of two chloroiridium phthalocyanine aggregates in α-chloronaphthalene between 5 and 80 K have revealed the existence of low-lying activated states only a few tens of cm−1 above the zero-point vibration in both lowest singlet and triplet states. From the data, activation energies of intersystem crossings between the two multiplicities associated with these states have been obtained as follows: for crossing from the first excited singlet to the lowest triplet state, Ea = 42 ± 10 and 29 ± 10 cm−1, respectively, for the two aggregates; for crossing from the lowest triplet to the ground singlet state, [Formula: see text] and 23 ± 5 cm−1, respectively. These activated states are tentatively attributed to certain intermolecular modes of vibration in aggregates. Specifically, they fit the model of molecular torsional oscillation of two and three parallel-sheet arrangements. On the basis of these findings, we propose that the first Ea (or [Formula: see text]) is the fundamental librational frequency of the dimer and the second Ea (or [Formula: see text]) is that for the trimer.