Linear concentration dependence of vibrational width and vibrational dephasing paths in aqueous nitrate solutions

A theoretical model of vibrational dephasing of Raman active ions in aqueous electrolyte solutions is presented in which a probe ion is coupled to the bath by direct ion-solvent and ion-ion interactions. Expression for the vibrational width in terms of concentrations and efficiencies of the vibrational frequency modulation by ion-perturber interactions is given in the fast modulation scheme. The observed linear concentration dependence of the vibrational dephasing width of the v ₁(A'₁) mode of NO₃ ^- in aqueous solutions is reasonably well explained from this model, and efficiencies of the dephasing paths through NO₃ ^--water hydrogen bonding interaction and contact NO₃ ^--cation pair formation interaction are estimated. Anions in the solution give only a secondary effect to nitrate vibrational dephasing because of interionic repulsive forces.     

Vibrational dephasing of spherical top anions in aqueous solutions

The vibrational dephasing times for spherical top anions in aqueous solutions calculated from in the shape of the isotropic Raman bands of the fully symmetric vibrations of anions, depending on the temperature and the nature of the anion, are analyzed. It is concluded that the dephasing rates for the anions and their temperature dependences can be reasonably explained within the framework of a model that describes the vibrational dephasing of a diatomic molecule interacting with a solvent molecule by using the Morse potential.     

Vibration-dependent trajectories and their effects on vibrational dephasing

We show that the expression for S₁ (i.e., the first term in the expansion of the S matrix) that is essential in calculating vibration-rotation pressure-broadened shifts is not properly given in the usual Robert-Bonamy (RB) formalism. The problem resulted when they considered effects of the vibrational dephasing on S₁; they tacitly made an assumption that the trajectories of interest are vibrationally independent. As a result, the current RB expression is an approximate one. Based on a vibration-dependent trajectory model, which is physically sound, we derive the correct expression for S₁. We present numerical calculations of the broadening and shifting cross sections and of the line shape parameters for the H₂-He pair and find for this molecular system, new results differ significantly from those calculated using the existing formalism. In addition, by comparing with those derived from close coupling calculations, we find that the new results are better than the old ones. Finally, we discuss how important effects from this modification could be for other molecular systems. We conclude that for certain molecular systems where the short-range collisions are the dominant source responsible for the line widths and shifts, and in addition, the isotropic potential has small depth, the present modification is a worthwhile step to be taken in order to refine the current RB formalism. Meanwhile, for other systems it may not be necessary.     

Vibrational analysis of cinchona alkaloids in the solid state and aqueous solutions

Cinchona alkaloids are well‐known antimalarial compounds also used in asymmetric synthesis in organic chemistry. In this work, vibrational spectra of quinine, quinidine, cinchonine, and cinchonidine were acquired and interpreted on the basis of theoretical calculations. Normal Raman spectra of the alkaloids in solution exhibit similar patterns and cannot be used for differentiation between the derivatives (e.g. quinine and cinchonidine) and corresponding pseudoenantiomers (e.g. quinine and quinidine). Thus, Raman Optical Activity (ROA) method was applied to show distinct differences related to the configuration of chiral atoms. ROA allowed unequivocal identification of the pseudoenantiomers based on the sign of the characteristic bands from a single measurement. The experiments were supported by the theoretical approach including conformational study followed by wavenumber calculations and Potential Energy Distribution (PED) analysis. For quinine, vibrational spectroscopy was additionally used to show its structural changes in aqueous solutions at various pH and its distribution in a pharmaceutical product. Spatial distribution of quinine in a drug was observed by the FT‐Raman mapping technique. Copyright © 2015 John Wiley & Sons, Ltd.     

Concentration effects in the vibrational spectra of aqueous solutions of nitrites

To whom correspondence should be addressd.     

Vibrational relaxation and line widths in liquids dephasing by intermolecular forces

A theory of vibrational relaxation in liquids is presented in which the vibrations are loosely coupled to a bath or lattice of molecular translations and rotations by intermolecular forces. Using the second-order perturbation expressions familiar from magnetic resonance the secular contribution to the line width is calculated. Different coupling paths are considered and expressions given for the line widths in a liquid mixture in terms of number densities and diffusion coefficients valid when reorientation is slow and translation diffusional.     

Photoluminescence of aqueous solutions of uranyl nitrate containing sodium tetrametaphosphate

Solutions (10^–5 to 5×10^–2 M) of UO₂(NO₃)₂ have been used in the presence of 2 wt.% Na₄P₄O₁₂, with excitation by a mercury arc over the range 3200–3800 Å. The emission and absorption spectra of the complex are reported; the first is narrow and has peaks at 4910, 5150, and 5400 Å. This spectrum is the same whether the tetrametaphosphate anion has the chair configuration or the boat one.     

Caffeine as non-toxic corrosion inhibitor for copper in aqueous solutions of potassium nitrate

Different electrochemical methods were employed in order to confirm the ability of caffeine (1,3,7-trimethylxanthine) to inhibit the corrosion processes of copper in aqueous potassium nitrate solutions in the absence and in the presence of chloride. Some experiments were repeated in potassium perchlorate in order to compare the influence of the medium. The interaction between the organic compound and the electrode surface occurs independently of the electrode potential. However, maximum interaction was observed at 0.0 V (Ag/AgCl) in aerated solutions, and at −0.25 V (Ag/AgCl) in deaerated solutions.The presence of the organic compound adsorbed on the electrode surface was confirmed by comparing the voltammograms of copper electrode in the absence and presence of 1.5 mmol L⁻¹ of dissolved caffeine. The same results were observed by comparing polarization curves in the absence and in the presence of caffeine.Anodic currents decrease noticeably in the presence of the organic compound. Chronoamperometric experiments were conclusive to prove the inhibitor capability of caffeine to decrease the corrosion dissolution processes of copper under anodic polarization.     

Entanglement, phase correlation and dephasing of two-qubit states

The relation between entanglement and phase correlation of two-qubit states is studied. Decoherence of entanglement and phase correlation caused by correlated classical noises is also investigated. It is found that the decay of the phase correlation is quite different from that of the entanglement when the finite-time disentanglement occurs.     

Structural and vibrational studies of anilinium nitrate

The crystals of anilinium nitrate, , were obtained by slow evaporation of an aqueous solution. The crystals belong to the Pbca (no. 61) space group of orthorhombic system, Z=8, a=10.158(2), b=9.277(2), c=16.177(3) Å. Positively charged anilinium cations and anions are present in the structure. Powder FT IR and FT Raman spectra for normal and deuterated samples are discussed with respect to the crystal structure. DSC measurements do not indicate clearly on the occurrence of phase transition in the temperature region 113-293 K.     

二维格子神经元网络的振动共振和非线性振动共振

本文采用数值模拟的方法, 在通过电突触耦合或化学突触耦合的二维格子神经元网络中, 研究了FitzHugh-Nagumo神经元受到双频信号输入时神经元网络对低频信号的响应特性. 结果表明:当固定受到双频输入信号的神经元在体系中所占的比例且FitzHugh-Nagumo神经元参数处于可激发区域时双频信号中的高频部分可诱导出动作电位产生, 而且随着高频输入信号强度的增加, 神经元网络对低频输入信号响应先增大后减小, 出现了极大值, 即发生了振动共振现象. 另外本文还研究了神经元网络对低频输入信号的二次谐波的响应, 同样发现了非线性振动共振现象, 并且体系对低频信号的响应随着其频率ω 的增加也产生共振现象, 即发生了双共振现象. 上述共振现象在以电突触耦合的二维格子神经元网络中和以化学突触耦合的二维格子神经元网络中都可以观察到. 当固定双频输入信号中高频输入信号强度时, 随着受到双频输入信号的神经元在体系中所占比例的变化, 电突触耦合的二维格子神经元网络对低频输入信号的响应与化学突触耦合的二维格子神经元网络对低频输入信号的响应相比有很大的不同.