Single-Ion Solvation Free Energy: A New Cluster-Continuum Approach Based on the Cluster Expansion Method

Accurate calculation of the solvation free energy of single ions remains an important goal, involving the development in the dielectric continuum solvation models, statistical mechanics with explicit solvent and hybrid...

Estudo fotofísico do Luminol

The 5-Amino-2,3-dihydro-1,4-phthalazinedione known as Luminol is used mainly in hidden blood investigations. Therefore, the objective of this work is to develop a calculations routine using computational chemistry methods that properly describe the structure of luminol and its derivatives. Posteriorly, this routine will be used for the analysis and the proposition of new structures comparing the results with experimental data obtained in appropriate literature. Firstly, the Density Functional Theory (DFT) was used with the functional B3LYP/G, and the base function def2-TZVP in the ORCA program for modeling the structures. Thus, was verified the interference of the presence of solvent molecules close to the luminol molecule, the use of solvent as a dielectric continuum, the combination of both for a description of the solvent effect, and the use of relativistic functions to optimize results. Therefore, having obtained the preliminary results, we did the comparison with experimental data collected by other researchers.

Effects of Density and Diameter on Surface Optical Phonon Modes in GaAs Nanowire Bundles

We report the systematic investigation of the surface optical phonon modes in Au-catalyzed GaAs nanowires grown on an Au pre-patterned GaAs(111)B substrate using μ-Raman spectroscopy. We employed electron-beam dose rate as a control parameter during the substrate patterning step for adjusting the nanowire base diameter and coverage, which are independent from the nanowire growth conditions. We have experimentally studied the effect of the fill factor and average diameter on the surface optical phonon modes and explained the red-shift and broadening of the surface optical phonon frequencies by employing the dielectric continuum model. The surface optical phonon mode shift is exhibited to be sensitive to fill factor, rather than base diameter. The decrease in the average diameter from 280 nm to 180 nm results in the asymmetric broadening and red-shift of the surface optical phonon frequency (~1.83 cm−1) but the theoretical calculation from the isolated single nanowire-based dielectric continuum model cannot solely explain the behaviors of the surface optical phonon mode. In contrast, the change in the fill factor from 0.01 to 0.83 results in a shift of the surface optical phonon frequency (~6.5 cm−1) from the GaAs bulk value. The red-shift and asymmetric broadening of the surface optical phonons, in an agreement with the Maxwell-Garnett approximation, are consequences of dipolar interaction of randomly aligned neighboring nanowires and the polar nature of GaAs nanowire bundles. This work suggests the pre-patterning parameter dependent surface optical phonon characteristics of GaAs nanowire bundles which are of great importance in the nondestructive characterization of low-dimensional opto-electronic materials and devices.

Effects of ternary mixed crystals on interface/surface optical phonon in spherical core-shell quantum dots

Within the framework of the dielectric continuum approach and modified random-element-isodisplacement model, the optical vibration mode in a spherical core-shell quantum dot (CSQD) consisting of ternary mixed crystals (TMCs) are investigated. The dispersion relation and electron–phonon interaction Hamiltonian are derived. As a typical case, the numerical results for [Formula: see text] and [Formula: see text] CSQDs are obtained and discussed. Taking the one- and two-mode behaviors of TMCs into account, the effects of TMCs on interface/surface optical (IO/SO) phonon show that there are 3 and 5 branches of IO/SO phonon modes in [Formula: see text] and [Formula: see text] CSQDs for a given component of TMC, respectively. It is also found that the IO/SO phonon frequencies and electron–phonon interactions are strongly dependent on the component of TMCs and the size of CSQDs. We hope this work would be useful for the study of the phonon-related photoelectric properties in CSQDs consisting of TMCs.

Hydration and Ion Pair Formation in Aqueous Lu3+- Solution

Aqueous solutions of Lu3+- perchlorate, triflate and chloride were measured by Raman spectroscopy. A weak, isotropic mode at 396 cm−1 (full width at half height (fwhh) at 50 cm−1) was observed in perchlorate and triflate solutions. This mode was assigned to the totally symmetric stretching mode of [Lu(OH2)8]3+, ν1LuO8. In Lu(ClO4)3 solutions in heavy water, the ν1LuO8 symmetric stretch of [Lu(OD2)8]3+ appears at 376.5 cm−1. The shift confirms the theoretical isotopic effect of this mode. In the anisotropic scattering of aqueous Lu(ClO4)3, five bands of very low intensity were observed at 113 cm−1, 161.6 cm−1, 231 cm−1, 261.3 cm−1 and 344 cm−1. In LuCl3 (aq) solutions measured over a concentration range from 0.105–3.199 mol·L−1 a 1:1 chloro-complex was detected. Its equilibrium concentration, however, disappeared rapidly with dilution and vanished at a concentration < 0.5 mol·L−1. Quantitative Raman spectroscopy allowed the detection of the fractions of [Lu(OH2)8]3+, the fully hydrated species and the mono-chloro complex, [Lu(OH2)7Cl]2+. In a ternary LuCl3/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH2)8−nCln]+3−n (n = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu3+- water cluster in vacuo and with a polarizable dielectric continuum (PC) model including the bulk solvent implicitly. The bond distance and angle for [Lu(OH2)8]3+ within the PC are in good agreement with data from structural experiments. The DFT frequencies for the Lu-O modes of [Lu(OH2)8]3+ and its deuterated analog [Lu(OD2)8]3+ in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu3+ (aq) is slightly lower than the experimental value.