scholarly journals Local mode interpretation of the OH overtone spectrum of 1:1 phyllosilicates

2021 ◽  
Vol 33 (2) ◽  
pp. 209-220
Author(s):  
Etienne Balan ◽  
Emmanuel Fritsch ◽  
Farid Juillot ◽  
Thierry Allard ◽  
Sabine Petit
Keyword(s):  
Near Infrared ◽  
Divalent Cations ◽  
Local Mode ◽  
Transition Elements ◽  
Vibrational States ◽  
Oh Groups ◽  
Mechanical Approach ◽  
Mir Spectra ◽  
Quantum Mechanical Approach ◽  
Theoretical Results

Abstract. Although OH overtone bands of 1:1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1:1 phyllosilicates. In this case, the overtone spectra cannot be directly related to their fundamental counterparts observed in the mid-infrared (MIR) spectra. In the present study, we use a parameterized quantum-mechanical approach to compute the vibrational frequencies related to the fundamental and overtone bands in serpentine group and kaolinite group minerals. The simple model is based on a description of the vibrational properties of a cluster of OH groups in terms of harmonically coupled anharmonic oscillators. The comparison of the theoretical results with experimental observations makes it possible to interpret most of the salient features of the overtone spectrum of 1:1 phyllosilicates. Unlike the bands observed in the MIR spectra, the overtone bands observed between 7000 and 7300 cm−1 are related to local transitions from the ground state to the second excitation level of OH groups, whereas the weaker bands observed between 7300 and 7400 cm−1 involve a double excitation to the first vibrational level of OH oscillators. The results also support the assignment of specific overtone bands to the occurrence of substituted divalent cations of transition elements in serpentine group minerals.

scholarly journals Effect of π-conjugated molecules on electronics properties of benzene-diamine derivatives

2021 ◽  
Vol 19 (50) ◽  
pp. 70-76
Author(s):  
Mohsin Al-Khaykanee ◽  
Ali Al-Jawdahb
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Pi Conjugated ◽  
Phenyl Rings ◽  
Mechanical Approach ◽  
Quantum Mechanical Approach ◽  
Chemical Groups ◽  
Theoretical Results

The present work shows a theoretical results that have been used the functional Hybrid of three parameters Lee-Yang-Parr (B3LYP) of the quantum mechanical approach for density functional theory with (Spanish Initiative for Electronic Simulations with Thousands of Atoms) SIESTA code. All calculations were carried out employing the used method at the Gaussian 09 package of programs. It was reported the main point for research on dominance of the bandgap of elongated pi-conjugated molecules by using different chemical groups replacing hydrogen atom in the most molecules that used in this work. The side groups creates another factor that controls the value of the band gap. The dihedral angle between the two phenyl rings plays more important role in controlling the band gap in these molecules.

scholarly journals DFT Modelling of Molecular Structure, Vibrational and UV-Vis Absorption Spectra of T-2 Toxin and 3-Deacetylcalonectrin

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 649
Author(s):  
Dmitrii Pankin ◽  
Mikhail Smirnov ◽  
Anastasia Povolotckaia ◽  
Alexey Povolotskiy ◽  
Evgenii Borisov ◽  
...  
Keyword(s):  
Density Functional ◽  
Quantum Mechanical ◽  
Theoretical Studies ◽  
Vibrational States ◽  
Mechanical Approach ◽  
Vibrational Spectroscopies ◽  
Quantum Mechanical Approach ◽  
Dft Modelling ◽  
Identification And Characterization

This paper discusses the applicability of optical and vibrational spectroscopies for the identification and characterization of the T-2 mycotoxin. Vibrational states and electronic structure of the T-2 toxin molecules are simulated using a density-functional quantum-mechanical approach. A numerical experiment aimed at comparing the predicted structural, vibrational and electronic properties of the T-2 toxin with analogous characteristics of the structurally similar 3-deacetylcalonectrin is performed, and the characteristic spectral features that can be used as fingerprints of the T-2 toxin are determined. It is shown that theoretical studies of the structure and spectroscopic features of trichothecene molecules facilitate the development of methods for the detection and characterization of the metabolites.

Experimental and Theoretical Investigations of Complex Formation of Substituted Phenylazo-Derivatives of Methylphloroglucinol

2016 ◽  
Vol 12 (8) ◽  
pp. 295-300
Author(s):  
Olga Kovalchukova ◽  
Amangdam A.T. ◽  
Strashnova S.B. ◽  
Strashnov P.V. ◽  
Romashkina E.P. ◽  
...  
Keyword(s):  
Complex Formation ◽  
Organic Ligand ◽  
Spectrophotometric Titration ◽  
Organic Ligands ◽  
Oh Groups ◽  
Tautomeric Forms ◽  
Theoretical Investigations ◽  
Derivatives Of ◽  
Theoretical Results ◽  
Titration Technique

Using spectrophotometric titration technique, the processes of complex formation of some phenylazo-derivatives of methylphloroglucinol (MPG) containing hydroxo-, nitro- and nitroso-substituents were studied. The spectral criteria of neutral and ionized forms of the organic ligands in their different tautomeric forms were determined.It was detected that the complex formation is accompanied by formation of one or two chelate cycles which involve azo- or nitroso-fragments and neighboring OH-groups of the organic ligands. Different types of coordination lead to different changes in the electronic absorption spectra.The DFT-B3LYP modeling of a Ni(II) complex of α-hydroxyphenylazo MPG established the most probable coordination mode of the organic ligand: tridentate chelating dianion, distorted square coordination of Ni-cations including one water molecule.  The theoretical results are in a good accordance with the experimental data.

scholarly journals Comparison of Spectroscopic Techniques Combined with Chemometrics for Cocaine Powder Analysis

2020 ◽  
Vol 44 (8) ◽  
pp. 851-860
Author(s):  
Joy Eliaerts ◽  
Natalie Meert ◽  
Pierre Dardenne ◽  
Vincent Baeten ◽  
Juan-Antonio Fernandez Pierna ◽  
...  
Keyword(s):  
Gas Chromatography ◽  
Near Infrared ◽  
Evaluation Criteria ◽  
Classification Model ◽  
Support Vector ◽  
Spectroscopic Techniques ◽  
Data Set ◽  
Promising Tool ◽  
Powder Analysis ◽  
Mir Spectra

Abstract Spectroscopic techniques combined with chemometrics are a promising tool for analysis of seized drug powders. In this study, the performance of three spectroscopic techniques [Mid-InfraRed (MIR), Raman and Near-InfraRed (NIR)] was compared. In total, 364 seized powders were analyzed and consisted of 276 cocaine powders (with concentrations ranging from 4 to 99 w%) and 88 powders without cocaine. A classification model (using Support Vector Machines [SVM] discriminant analysis) and a quantification model (using SVM regression) were constructed with each spectral dataset in order to discriminate cocaine powders from other powders and quantify cocaine in powders classified as cocaine positive. The performances of the models were compared with gas chromatography coupled with mass spectrometry (GC–MS) and gas chromatography with flame-ionization detection (GC–FID). Different evaluation criteria were used: number of false negatives (FNs), number of false positives (FPs), accuracy, root mean square error of cross-validation (RMSECV) and determination coefficients (R2). Ten colored powders were excluded from the classification data set due to fluorescence background observed in Raman spectra. For the classification, the best accuracy (99.7%) was obtained with MIR spectra. With Raman and NIR spectra, the accuracy was 99.5% and 98.9%, respectively. For the quantification, the best results were obtained with NIR spectra. The cocaine content was determined with a RMSECV of 3.79% and a R2 of 0.97. The performance of MIR and Raman to predict cocaine concentrations was lower than NIR, with RMSECV of 6.76% and 6.79%, respectively and both with a R2 of 0.90. The three spectroscopic techniques can be applied for both classification and quantification of cocaine, but some differences in performance were detected. The best classification was obtained with MIR spectra. For quantification, however, the RMSECV of MIR and Raman was twice as high in comparison with NIR. Spectroscopic techniques combined with chemometrics can reduce the workload for confirmation analysis (e.g., chromatography based) and therefore save time and resources.

Quantitative Prediction of Aggregation‐Induced Emission: A Full Quantum Mechanical Approach to the Optical Spectra

2020 ◽  
Vol 132 (28) ◽  
pp. 11647-11652
Author(s):  
Wei Zhang ◽  
Jinfeng Liu ◽  
Xinsheng Jin ◽  
Xinggui Gu ◽  
Xiao Cheng Zeng ◽  
...  
Keyword(s):  
Optical Spectra ◽  
Quantitative Prediction ◽  
Quantum Mechanical ◽  
Aggregation Induced Emission ◽  
Mechanical Approach ◽  
Quantum Mechanical Approach ◽  
Full Quantum

High resolution spectra of GeH4v=6 and 7 stretch overtones. The perturbed local mode vibrational states

1993 ◽  
Vol 99 (4) ◽  
pp. 2359-2364 ◽  
Author(s):  
Qing‐Shi Zhu ◽  
A. Campargue ◽  
J. Vetterhöffer ◽  
D. Permogorov ◽  
F. Stoeckel
Keyword(s):  
High Resolution ◽  
Local Mode ◽  
Vibrational States

Computational Studies of Magnesium and Strontium Substitution in Hydroxyapatite

2012 ◽  
Vol 529-530 ◽  
pp. 123-128 ◽  
Author(s):  
Flora E. Imrie ◽  
Marta Corno ◽  
Piero Ugliengo ◽  
Iain R. Gibson
Keyword(s):  
Density Functional ◽  
Structural Changes ◽  
Harmonic Approximation ◽  
Site Preference ◽  
Ionic Radii ◽  
Biologically Relevant ◽  
Site Preferences ◽  
Mechanical Approach ◽  
Quantum Mechanical Approach ◽  
Mg Substitution

The properties of hydroxyapatite can be improved by substitution of biologically relevant ions, such as magnesium (Mg) and strontium (Sr), into its structure. Previous work in the literature has not reached agreement as to site preferences in these substitutions, and there are suggestions that these may change with differing levels of substitution. The current work adopted a quantum mechanical approach based on density functional theory using the CRYSTAL09 code to investigate the structural changes relating to, and site preferences of, magnesium and strontium substitution (to 10 mol%) in hydroxyapatites and also to predict the corresponding vibrational spectra in the harmonic approximation. The structures underwent full geometrical optimisation within the P63 space group, indicating an energetic site preference for the Ca (2) site in the case of Mg substitution, and the Ca (1) site in the case of Sr. Shrinkage of the unit cell was observed in the case of Mg substitution, and expansion in the case of Sr substitution, in agreement with the corresponding ionic radii. Thermodynamic properties of the structures obtained from the harmonic vibrational frequency calculations confirmed that the structures were minima on the potential energy surface. Isotopic substitutions indicated that the main contribution of Sr and Mg to vibrational modes is at frequencies < 400 cm-1.

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