Dynamics and spectra of excited states of water-micellar suspensions of single-walled carbon nanotubes

The dynamics of the photoinduced differential absorption and excited-state bleaching spectra of single-walled carbon nanotubes suspended in a micellar solution were studied in the spectral range from 40 to 1000 nm within a time interval from 70 fs to 150 ps under excitation by 50-fs pulses with photon energies 2 and 4 eV. The bleaching and absorption bands were observed in the spectra; the positions of the bleaching peaks were independent of the photon energy of the exciting femtosecond pulse in the range 2–4 eV. It was established that, for delay times shorter than 1 ps, the shape of the differential spectrum of excited nanotubes coincided with the shape of the second derivative of the absorption spectrum of unexcited nanotubes in the frequency range of exciting pulse above 18000 cm^?1 (the range of absorption bands of metallic nanotubes). In the frequency range below 16000 cm^?1 (the range of absorption peaks of semiconducting nanotubes), the bleaching peaks in the differential spectrum of excited nanotubes undergo a high-frequency shift of 200–300 cm^?1 with respect to the second-derivative spectrum of unexcited nanotubes. The excited-state relaxation rate constants were measured. They are well approximated by the exponential dependences and depend on the probe-pulse wavelength. An assumption was made about the nature of the observed spectra of excited nanotubes and about the excitation relaxation.     

Illumination of the shadow zone in a two-channel oceanic waveguide with a fine structure of sound speed inhomogeneities

The experimental data on the sound field structure, which were obtained by emitting a continuous pseudonoise signal (a midfrequency of 3.2 kHz) in a two-channel oceanic waveguide, are compared with the calculations performed by the wave program with allowance for the fine structure of the sound speed inhomogeneities. A considerable increase in the intensity of the sound field with a definite angular spectrum is observed in the upper channel in the first shadow zone, and, in the experiment, the increase begins nearer to the sound source than predicted by the wave and ray calculations for a smooth sound speed profile. These features of the field structure are explained by the illumination of the shadow zone by the regular scattering of signals from highly anisotropic fine-structure inhomogeneities of the sound speed profile, which are clearly pronounced in the region of the given oceanic experiment.     

Theory of the singular quantum oscillator

We propose a number of arguments in favor of reevaluating the theory of a quantum oscillator described by the Hamiltonian H=–d²/dx² + 2²x² + x^–2(=2m=1). We propose that functions ₊(x) which continuously reduce to even harmonic oscillator solutions in the 0 limit be taken as the even solutions of the Hamiltonian in the –1/4 < < 3/4 range. In this scheme the problem becomes truly one-dimensional such that even and odd parity energy levels alternate, whereas the usual approach leads to parity degeneracy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 85–89, October, 1989.     

Dynamics of intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules

Intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules were studied by femtosecond laser spectroscopy. Experiments were carried out with two types of compounds, namely, those experiencing intramolecular proton transfer and two model compounds in which it is impossible. Schemes of the processes studied were proposed and the characteristic rate constants were determined. The excited-state intramolecular proton transfer (ESIPT) in the molecules with planar structure of the reaction center is a very fast process (100 fs). If the reaction center has a nonplanar structure and, hence, the intramolecular hydrogen bond is weakened, the ESIPT time is determined by the time of conformational rearrangement of the molecule.     

Heat effects and rates and molecular mechanisms of water sorption by perfluorinated polymer materials bearing functional groups

The heat effects and the rates and equilibrium quantities of H₂O vapour sorbed and desorbed on polymeric perfluorinated materials (functional groups -SO₃H, -SC₃Na, -SO₃K) and on material treated with FeCl₃ solution as sorbent were investigated.Sorbed H₂O may be completely desorbed in vacuum at 443 K. The material bearing -SO₃H has maximum sorption affinity: the molar heat of -SO₃H wetting is close to that of H₂SO₄ wetting. The differential heat of sorption decreases from 68 kJ mol^–1 atn0(n=H₂O/-SO₃H) to 45 kJ mol^–1 atn5, but not below the heat of H₂O condensation. The -SO₃H samples sorb H₂O vapour in the presence of liquid H₂O at 293 K up ton=17. The -SO₃K material has minimum affinity for H₂O: the equilibrium quantity sorbed in room air is less by a factor of 4 than that for the -SO₃H material. The spatial arrangement of H₂O molecules near the sulpho groups is considered.     

A <Superscript>1</Superscript>H NMR study of radical copolymerization of <Emphasis Type="Italic">N</Emphasis>-vinylsuccinimide with <Emphasis Type="Italic">n</Emphasis>-butyl acrylate in dimethyl sulfoxide

Kinetic features of radical copolymerization of N-vinylsuccinimide with n-butyl acrylate in dimethyl sulfoxide were studied by ¹H NMR spectroscopy. The dependences of the running concentrations of the monomers and of the “instant” and overall compositions of the copolymers on the reaction time were determined. The limiting conversions were established for correct analysis of the kinetic features of copolymerization at essentially different relative activities of the monomers. The copolymerization constants and the probability of alternation of the units in the copolymer chains were calculated. Original Russian Text E.V. Sivtsov, A.I. Gostev, N.A. Lavrov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1679–1682.     

Inverse quantum mechanics problem for potentials with λx−2 singularities

Using a one-dimensional oscillator with a x^–2-singular potential as an example, a method of solving an inverse problem of quantum mechanics with the same singularity of the potential is given. A nontrivial form of corrections to the potential due to a change in the spectral parameters is found.Translated frpm Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 57–61, September, 1991.     

Determination of the mean energy of backscattered electrons in dependence on the exit angle

A semiconductor detector was used to measure the mean energy of backscattered electrons as a function of the exit angle. New regularities of electron backscattering were found. A nonmonotonic dependence of the mean energy of backscattered electrons on the exit angle and the primary electron energy for materials with different atomic numbers was revealed.