Vibrational spectra and dynamics of conformation and hydrogen bonding of n-methylacetamide. I. Conformational dynamics of the CH3CONHCH3 molecule and NH out of plane band splitting

The infrared spectra of CH₃CONHCH₃ and CH₃CONDCH₃ have been investigated as low temperature crystals, pure liquids and solutions in various solvents in the 400-800 cm^?1 range. A new assignment of the bands associated with the NH group is given. Multiplets of γ NH and γ ND fundamentals have generally been observed and have been interpreted in terms of a double minimum potential function of the γ NH mode with a tunnelling between two minima. The potential functions of γ NH and τ CN modes are similar and can be combined to give a potential surface with four minima corresponding to four molecular conformations. The influence of the hydrogen bonding on the γ NH splitting and barrier height is discussed.     

Spontaneous and stimulated luminescence of CdSe

Luminescence of CdSe excited by various high density excitations at the temperature range from 77 to 300°K has been investigated. The luminescence temperature dependence and the photo-conductivity and luminescence dependences on intensity are discussed in terms of exciton-electron and exciton-exciton interaction. The “resonance” type model for latter interaction is proposed.     

Effects of selenium treatment on composition and photoluminescence properties of porous silicon

In this work, an ultrasonically enhanced anodic electrochemical etching is developed to fabricate light-emitting porous silicon material. Porous silicon layer is fabricated in n-type (1 0 0) oriented silicon using HF solution and treated in selenious acid to increase the photoluminescence intensity. It is found that the increase of photoluminescence intensity after selenious acid treatment is higher in the intact zones and lower in the detached zones of ultrasonic excitation. The photoluminescence appears as a non-monotonous function of time exposure of selenious acid treatment. Surface chemical composition analysis by X-ray photoelectron spectroscopy shows formation of Si-Se_x and Si-Se_x-O_y on the surface of porous silicon treated with the selenious acid.     

Cold atom dynamics in non-Abelian gauge fields

The dynamics of ultracold neutral atoms subject to a non-Abelian gauge field is investigated. In particular we analyze in detail a simple experimental scheme to achieve a constant, but non-Abelian gauge field, and discuss in the frame of this gauge field the non-Abelian Aharanov–Bohm effect. In the last part of this paper, we discuss intrinsic non-Abelian effects in the dynamics of cold atomic wavepackets. PACS 03.75.Hh     

Surface-mediated nucleation in the solid-state polymorph transformation of terephthalic acid

A molecular mechanism for nucleation for the solid-state polymorph transformation of terephthalic acid is presented. New methods recently developed in our group, aimless shooting and likelihood maximization, are employed to construct a model for the reaction coordinate for the two system sizes studied. The reaction coordinate approximation is validated using the committor probability analysis. The transformation proceeds via a localized, elongated nucleus along the crystal edge formed by fluctuations in the supramolecular synthons, suggesting a nucleation and growth mechanism in the macroscopic system.     

Generalized Green’s functions for the second-order discrete problems with nonlocal conditions

In this paper, we investigate a generalized discrete Green’s function that describes the general least squares solution of every second-order discrete problem with two nonlocal conditions. We develop the problem where the necessary and sufficient existence condition of ordinary discrete Green’s function is not satisfied. Some examples are also presented.     

On the roots of the equation \zeta (s)=a

Given any complex number $a$ , we prove that there are infinitely many simple roots of the equation $\zeta (s)=a$ with arbitrarily large imaginary part. Besides, we give a heuristic interpretation of a certain regularity of the graph of the curve $t\mapsto \zeta ({1\over 2}+it)$ . Moreover, we show that the curve $\mathbb {R}\ni t\mapsto (\zeta ({1\over 2}+it),\zeta '({1\over 2}+it))$ is not dense in $\mathbb {C}^2$ .