Photocatalytic Activity of g-C3N4 in the Partial Oxidation of Benzyl Alcohol Under Visible Light

Theoretical and Experimental Chemistry - It is shown that post-synthetic thermal treatment of graphitic carbon nitride (g-C3N4), obtained by pyrolysis of melamine, in molten potassium and lithium...     

On the mechanism of oxidation process initiation by the N-hydroxyphthalimide-cobalt (II) acetate system

The effect of the structure of radical catalysts, N-hydroxyphthalimides (NHPI), on the oxidation process initiation in the presence of cobalt (II) acetate is studied. It is shown that the magnitude of the synergic effect of the system NHPI-Co(OAc)₂ depends on the structure of NHPI molecule. The proposed mechanism is confirmed according to which of the NHPI molecules in the inner sphere of the metal are catalytically active.     

The possibility of using femtosecond IR spectroscopy to determine the composition of molecules in the gas phase

The possibility of using one method of femtosecond laser spectroscopy, IR pump-probe, is considered for analyzing the molecular composition of gas. The measured intramolecular relaxation time of the vibrational energy is proposed as an individual characteristic of molecules. A number of compounds of different classes having the molecular chromophore group C=O are investigated. It is shown that the characteristic relaxation times of the corresponding analytical signals in the resonant exciting of C=O vibrations are significantly different for different molecules (ten or more), making it possible to identify molecules in mixtures by means of temporal selection. The linear dependence of the analytical signal on the vapor pressure of the investigated compounds and the energy fluence of the exciting radiation is revealed. It is shown that the analytical signal is not dependent on the pressure of the buffer gas (nitrogen) up to 1 atm.     

Multistability in optical transmittance of spatial light modulators with internal feedback

A multistable spatial optical device has been developed on the basis of a spatial light modulator which contains photosensitive and electrooptical liquid crystal layers where an internal feedback loop is established.     

Dynamics of photoprocesses induced by femtosecond infrared radiation in free molecules and clusters of iron pentacarbonyl

The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO)₅ molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO)₅⁺ molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO)₅]_n clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the “evaporation ensemble” concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO)₅]_n clusters have been estimated.     

Parameters of a Light Bullet

JETP Letters - The absolute parameters of a light bullet formed upon the filamentation of femtosecond mid-infrared radiation under the conditions of anomalous group velocity dispersion have been...     

Effect of phase modulation of a laser pulse on the generation of a coherent totally symmetric phonon in a tellurium single crystal

The effect of phase modulation (resulting in a chirp of an ultrashort laser pulse) on the generation of a coherent A ₁ phonon in Te was studied. The amplitude of coherent oscillations was found to depend on the sign and value of the pulse chirp: the oscillation amplitude decreases as the chirp increases. For a positive chirp, this effect is twofold stronger than for a negative one. The frequency-resolved response of a bandwidth-limited pulse was studied, which revealed the difference of oscillations and the relaxation response for the Stokes and anti-Stokes frequencies. The detected phenomena can be used for coherent control of lattice dynamics.     

Action of N-hydroxyphthalimide on chain stereoregularity in the radical polymerization of methyl methacrylate

N-Hydroxyphthalimide (NHPI) has a dual function in the radical polymerization of methyl methacrylate (MMA): this compound acts as an initiator and also provides for stereochemical control of the polymer chain. Lowering the polymerization temperature leads to increased syndiotactic specificity in the polymethyl methacrylate molecule. The action of NHPI as an initiator and stereoregulator is attributed to the capacity of this compound to form a hydrogen bond with the monomer molecule and growing macroradical.     

Circular Dichroism Spectra of DNA Dispersions and Textures of DNA Phases

Optics and Spectroscopy - Circular dichroism (CD) spectra of liquid crystalline dispersions formed as a result of phase exclusion of double-stranded DNA molecules from aqueous-salt-poly(ethylene...     

Ultrahigh-spatial-resolution photoelectron projection microscopy using femtosecond lasers

Ultrahigh spatial resolution of two-photon photoelectron images (as high as 3 nm, which is the best value that has been achieved to date in photoelectron microscopy with spatial resolution) is obtained when silicon nanotips are irradiated by the second harmonic of a pulsed femtosecond Ti: sapphire laser. In addition, the absolute value of the two-photon external photoeffect coefficient is measured. Zh. éksp. Teor. Fiz. 115, 1680–1688 (May 1999)