Preparation, crystallographic characterization and theoretical study of two isomers of C70(CF3)12

Two isomers of C70(CF3)12 have been isolated from a mixture obtained by trifluoromethylation of C70 with CF3I; their molecular structures determined by X-ray crystallography are in good agreement with the results of theoretical DFT calculations for the most stable C70(CF3)12 isomers.     

Experimental and theoretical study of the electronic spectrum of the methylene amidogen radical (H2CN): verification of the 2A1 <-- 2B2 assignment

A collaborative experimental and theoretical study of the electronic spectrum and excited-state photochemistry of H(2)CN has been carried out. The absorption spectrum, in the range of 287-278 nm, was measured through cavity ring-down spectroscopy. The radical was prepared by 193 nm photolysis of monomeric formaldoxime vapor. Two diffuse features were observed in the 34800-35800 cm(-1) spectral range, along with the A-X (1,0) band of the OH cofragment. The broad features were assigned through high-level ab initio calculations as vibronic transitions to the ground and 2b(1) (umbrella mode) levels of the second excited B (2)A(1) state from the ground X (2)B(2) state of H(2)CN. Rotational constants for the lower and upper levels of these transitions were computed from the expectation values of the moments of inertia tensor, using the appropriate vibrational wave functions. Experimental and simulated rotational profiles of these bands agree extremely well with each other for an assumed type-B electric dipole-allowed (2)A(1) <-- (2)B(2) transition appropriate to this transition. The former assignment to the dipole-forbidden (2)B(1) <-- (2)B(2) transition can be ruled out by these results. A theoretical investigation of the dissociation pathways for electronically excited H(2)CN is also presented. The upper states of the observed bands cannot dissociate directly but rather decay through internal conversion and subsequent dissociation to H + HCN fragments; higher b(1) levels are above the excited-state dissociation limit.     

Vibrational analysis of the H5O2+ infrared spectrum using molecular and driven molecular dynamics

Standard molecular and driven molecular dynamics are used to analyze prominent spectral features in the H5O2+ infrared spectrum. In the driven method, the molecular Hamiltonian is augmented with a time-dependent term, mu x epsilon(0) sin(omegat), where mu is the dipole moment of H5O2+, epsilon0 is the electric field, and omega is the frequency. The magnitude of the electric field determines whether the driving is mild (the harmonic limit) or strong (anharmonic motion and mode coupling). We analyze the spectrum in the wavenumber range from 600 to 1900 cm(-1), where recent experimental measurements are available for H5O2+. On the basis of the simulations, we have assigned the broad feature around 1000 cm(-1) to the proton transfer coupled with the torsion motion. Intense absorption near 1780 cm(-1) is assigned to the H2O monomer bend coupled with proton transfer.     

All Stable Characteristic Classes of Homological Vector Fields

An odd vector field Q on a supermanifold M is called homological, if Q ² = 0. The operator of Lie derivative L _Q makes the algebra of smooth tensor fields on M into a differential tensor algebra. In this paper, we give a complete classification of certain invariants of homological vector fields called characteristic classes. These take values in the cohomology of the operator L _Q and are represented by Q-invariant tensors made up of the homological vector field and a symmetric connection on M by means of the algebraic tensor operations and covariant differentiation.     

A Nonholonomic Model of the Paul Trap

In this paper, equations of motion for the problem of a ball rolling without slipping on a rotating hyperbolic paraboloid are obtained. Integrals of motions and an invariant measure are found. A detailed linear stability analysis of the ball’s rotations at the saddle point of the hyperbolic paraboloid is made. A three-dimensional Poincaré map generated by the phase flow of the problem is numerically investigated and the existence of a region of bounded trajectories in a neighborhood of the saddle point of the paraboloid is demonstrated. It is shown that a similar problem of a ball rolling on a rotating paraboloid, considered within the framework of the rubber model, can be reduced to a Hamiltonian system which includes the Brower problem as a particular case.     

Controlled Free-Radical Copolymerization of N-vinyl succinimide and n-Butyl acrylate via a Reversible Addition–Fragmentation Chain Transfer (RAFT) Technique

Summary : Copolymerization of N-vinyl succinimide and n-butyl acrylate in the presence of dibenzyl trithiocarbonate as a reversible addition-fragmentation chain transfer agent was investigated. The linear dependence of molecular mass on conversion and low values of polydispersity index confirmed pseudo-living mechanism of the process. For the first time the soluble copolymers of N-vinyl succinimide and n-butyl acrylate with high composition homogeneity have been synthesized by copolymerization in bulk. The copolymerization kinetics was studied by NMR ¹H spectroscopy; the reactivity ratios were determined: r_VSI = 0.11, r_BA = 2.54. The copolymer microstructure was estimated; it was shown that in conditions of RAFT polymerization gradient copolymers enriched with BA on the tails of the macromolecule and with VSI in the middle can be obtained. The method of elimination of trithiocarbonate fragment by the reaction with an excess of AIBN was proposed leading to formation of the simplest gradient structure of N-vinyl succinimide – n-butyl acrylate copolymer.     

Surface-assisted transient displacement charge technique. I. Photoinduced charge transfer in self-assembled monolayers

Surface-assisted photoinduced transient displacement charge (SPTDC) technique was developed in order to study light-induced charge transfer in surface-bound molecules and applied to investigation of self-assembled monolayers of 7-diethylaminocoumarin and 2,4-dinitrophenylamine. The dipole moment change measured by SPTDC correlates reasonably well with that measured in solution by standard PTDC technique and with semiempirical calculations. Shortening of the excited-state lifetime of surface-immobilized coumarin due to stimulated emission was observed in both fluorescence and dipole measurements. The dipole signal decline in low-polarity solvents indicates the importance of dipole-dipole interaction that causes reorientation of molecules upon photoexcitation.     

Ring intermittency in coupled chaotic oscillators at the boundary of phase synchronization

A new type of intermittent behavior is described to occur near the boundary of the phase synchronization regime of coupled chaotic oscillators. This mechanism, called ring intermittency, arises for sufficiently high initial mismatches in the frequencies of the two coupled systems. The laws for both the distribution and the mean length of the laminar phases versus the coupling strength are analytically deduced. Very good agreement between the theoretical results and the numerically calculated data is shown. We discuss how this mechanism is expected to take place in other relevant physical circumstances.