Ultraviolet Absorption Spectra Research Articles

A Spontaneously Electrical State of Matter.

ConspectusMolecular deposition on solid surfaces forms crystalline or amorphous/glassy thin solid films. Intermolecular interactions govern the packing and dynamics of these films. The connection between molecular structure and intermolecular interactions is based on understanding electrostatic forces, dispersion forces and hydrogen bonding. Recently, an entire class of dipolar molecular species have demonstrated counterintuitive self-organization such that the dipole moments of individual molecules are oriented in thin films. This leads to the spontaneous generation of polarized molecular films manifesting a polarization charge equivalent to tens to hundreds of volts in strength at the film-vacuum interface, relative to the film-substrate interface. These voltages, and the corresponding electric fields present in such films, result from a collective and spontaneous orientation of molecular dipoles throughout the film during film growth and represent a metastable state of polarized material. The existence of these materials should encourage reconsideration of the importance of solid-state intermolecular electrostatic interactions.This account will detail observations of the spontaneous electric fields in molecular solids, provide insights into the dynamics and structure of molecular materials that the emergence of these electric fields can facilitate, and present a dipole-alignment based mean-field model that reproduces the temperature dependence of the electric field strength. Species as diverse as carbon monoxide, nitrous oxide, freons, simple alcohols, and cis-methyl formate have been demonstrated to spontaneously generate electric fields. We have reported electric fields more than 108 V m-1, have shown how field strength varies with the film deposition temperature, and have reported temperature-dependent Stark shifts observable in both infrared and ultraviolet absorption spectra. The latter has led to the reporting of large Wannier-Mott excitons in wide band gap molecular materials, such as solid carbon monoxide and ammonia.Changes in the field strength with time, at specific temperatures, can be related to the structural dynamics of glassy molecular solids. Measurement of surface potentials is a very sensitive technique by which to observe the rotation and translation of molecular species buried in thin films. This is particularly true for polarized, supercooled molecular glasses, where surface potentials have been used to report on secondary relaxation processes that have hitherto been hidden from measurement.Characterizing spontaneously electric molecular films, and understanding their behavior, requires the inclusion of nonlocal and nonlinear effects. The mean-field model that we present describes the data by connecting the energy of interaction of an average dipole with the mean effective field in the film, where this field is itself a function of the degree of polarization. This feedback loop produces a smooth function with a nonintuitive, discontinuous differential. The condensation of thin molecular films is an important means by which molecular solids are generated in the interstellar medium and represents a key pathway for the generation of organic optically and electrically active materials. It may also be possible to manipulate chemistry with the intense, localized electric fields acting as or acting on catalysts. The repercussions of the spontaneous generation of bound surface charges and the presence of electric fields in molecular solids will be discussed in these contexts.

Fluorescence sensing of ammonia in water using lead-free perovskite Cs2AgInCl6:Bi

Ammonia (NH3) is a common pollutant in water and an important indicator of environmental pollution. Its determination is of great significance to environmental protection. We synthesized ligand-free Cs2AgInCl6:Bi at room temperature to establish a low toxicity, rapid, and simple fluorescence assay for the selective determination of NH3 in water. Studies have shown that there is a good linear relationship with the concentration of NH3 in the range of 1.00 ∼ 20.00 mg L-1 and the determination limit is 0.40 mg L-1. The selectivity for NH3 is higher than other substances may exist in the water (eg. Na+, SO42-). Subsequently, X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, time-resolved fluorescence spectroscopy and ultraviolet absorption spectra were used to investigate the possible mechanism of NH3 reaction with Cs2AgInCl6:Bi. The water samples of lakes and rivers were analyzed by the proposed method and indophenolblue method, the results shown that there is no significant difference between the two methods. The reliable results (0.1%< RSD < 4.1%) and the satisfactory recovery (99.0%∼102.5%) were obtained by direct determination method and mark recovery method. Therefore, the simple, rapid and low-toxicity fluorescence method established in this work provides a promising approach for NH3 analysis in environmental water.

The Design, Synthesis and Application of Nitrogen Heteropolycyclic Compounds with UV Resistance Properties.

Exposure to ultraviolet (UV) light is known to cause skin aging, skin damage, cancer, and eye diseases, as well as polymer material aging. Therefore, significant attention has been devoted to the research and development of UV absorbers. Considering the robust hydrogen bonding and conjugated structure present in nitrogen-containing polycyclic compounds, these compounds have been selected as potential candidates for exploring ultraviolet absorption properties. After structural optimization and the simulation of ultraviolet absorption spectra, four tris-[1,2,4]-triazolo-[1,3,5]-triazine (TTTs) derivatives, namely TTTB, TTTD, TTTJ, and TTTL, were selected as the preferred compounds and synthesized. The structure of the compound was determined using various analytical techniques, including FTIR, 1HNMR, 13CNMR, HRMS, and XRD. Subsequently, composite films of polyvinyl chloride (PVC) and TTTs were produced using a simple solvent casting technique. The PVC films were subjected to UV age testing by exposing them to an ultraviolet aging chamber. The age-resistant performance of the fabricated films was evaluated using an ultraviolet spectrophotometer and Fourier infrared spectrum instrument. The findings suggest that TTTs exhibit a noteworthy capacity for absorbing ultraviolet radiation. The TTTL compound exhibits a superior UV absorption performance compared to commercially available UV absorbers such as UV-0 and UV-327 in the market.

The effect of zinc oxide on the physical and optical characteristics of calcium oxide containing boro-tellurite glasses

Glassy system with a chemical compositions of xZnO-10CaO-30TeO2-(60-x)B2O3 (x = 0 to 20 mol% with stepwise 5 mol%) was synthesized by conventional melt quenching method. The non-crystallinecharacter of the produced glasses was verified by X-ray diffraction analysis. Variations in the molar concentration of additional ZnO resulted in a densityrange of 3.19–3.77 g/cm3 for the current glasses. Through analysis of Ultraviolet Absorption spectrum, optical properties like cut-off (λc) optical energy band gap (Eopt), Urbach energy (ΔE),refractive index were determined. The cut-off wave length (λc) was increased, whereas, indirect band gap energy decreased with addition of ZnO content. The Urbach energy (ΔE) of the present glasses increased with ZnO content which confirms more disorderness. As the amount of ZnO in the glass system changed, the refractive index shifted from 2.23 to 2.30 with changing of ZnO content. The FTIR spectra confirmed the structural changes with increasing ZnO content. The higher refractive index values of the studied glasses and the presence TeO2 and ZnO enables the prominence of the glasses for NLO and antimicrobial applications.

Novel composite polymer-amended bentonite for environmental containment: Hydraulic conductivity, chemical compatibility, enhanced rheology and polymer stability

This study developed a novel composite polymer-amended bentonite consisting of two linear polymers (i.e., polyanionic cellulose (PAC) and hydroxypropyl methylcellulose (HPMC)) for use as an engineered barrier material in environmental containment applications. Several series of laboratory experiments were conducted on bentonite and polymer-amended bentonites with different PAC-HPMC mass ratios to evaluate free swell index and liquid limit using deionized water and 20 mM cadmium nitrate (Cd(NO3)2) as a typical contaminant. Hydraulic conductivity of bentonite and polymer-amended bentonite filter cakes was determined via modified fluid loss (MFL) tests using 20 mM Cd(NO3)2 solution under increasing pressure conditions. Rheological properties, such as apparent viscosity and shear stress, were measured, and yield stresses were estimated using the Bingham plastic and Herschel–Bulkley models to evaluate polymer stability. The results showed that exposure to 20 mM Cd(NO3)2 solution reduced both free swell index and liquid limit of bentonites with and without polymer-amendment. The bentonite amended with PAC-HPMC mass ratio of 7 (i.e., (P7H1)B) possessed the lowest hydraulic conductivity among the bentonites tested. Its hydraulic conductivity was one to two orders of magnitude lower than that of unamended bentonite. The ultraviolet absorption spectra analyses revealed the value of the wavelength of maximum absorption bands for (P7H1)B slurry was 11.9% greater than that for PAC-amended bentonite slurry, indicating stronger hydrogen bonding strength of (P7H1)B slurry. The total organic carbon in the filtrate for HPMC-amended bentonite slurries was 64.0–67.7% lower than that for PAC-amended bentonite slurries in the MFL tests. In addition, the total organic carbon in the filtrate decreased with increasing yield stress of polymer-amended bentonite slurries, indicating yield stress can be used as a good indicator for evaluating polymer stability in the polymer-amended bentonite filter cakes.

Hydrogen sulfide measurement of combustion gaseous product using ultraviolet absorption spectroscopy

Measurement of hydrogen sulfide (H2S) in gaseous product can provide direct reference for high-temperature corrosion of industrial combustion equipment. Aiming at the interference effect of overlapping measurement of absorption spectrum for H2S and other combustion gas components in UV absorption spectroscopy, the simulation calculation of ultraviolet band absorption spectrum of the typical gaseous products of coal combustion were carried out. The cross interference effects of combustion gaseous products were analyzed in detail. Due to the SO2 and H2S gas under typical combustion condition have equivalent absorption strength in the 228 nm-233 nm band, the influence of SO2 on H2S concentration inversion must be emphatically considered, and the inversion algorithm of H2S gas concentration under the background interference of combustion gaseous products SO2 was put forward. In order to validate the measurement accuracy by the inversion algorithm, the measurement experiments of gas mixture of H2S and SO2 were carried out. The results show that the algorithm can effectively solve the problem of cross interference between the detection of H2S and SO2 in the combustion gaseous products by UV absorption spectroscopy. On this basis, the sampling, pre-treatment and H2S gas concentration measurement system for boiler flue gas near the wall was developed and applied to measure H2S concentration of flue gas near the wall in a 1000 MW ultra-supercritical coal-fired power generation boiler. The results can provide important references for combustion adjustment and high-temperature corrosion prevention of boiler.

Application of machine learning algorithms for prediction of ultraviolet absorption spectra of chromophoric dissolved organic matter (CDOM) in seawater

The ultraviolet absorption spectra of chromophoric dissolved organic matter (CDOM) can be used to trace its sources and to explore the dynamic of the CDOM pool. In previous studies, only the spectra above 240 nm can be used directly to characterize the CDOM in seawater, due to the overlapping of CDOM absorption spectra below 240 nm with inorganic chemicals such as NO3−, NO2−, Cl- and Br-. In this study, three different machine learning models, back propagation neural network (BPNN), random forest (RF) and extreme gradient boosting (XGBoost), were built to predict the CDOM ultraviolet absorption spectra between 215 and 350 nm after being trained with the raw absorption spectra of seawater. The optimal input wavelength range of the raw seawater spectra is 250-350 nm, and the optimal model parameters of machine learning algorithms were determined by using five-fold cross validation. The results show that the three models can well predict the CDOM absorption spectra. Comparatively, the XGBoost model gave the best prediction results. The reasons might be related to the fact that the XGBoost algorithm focuses on the residuals generated by the last iteration, which can reduce both variance and bias, especially for datasets with small sample sizes. Based on the predicted spectra by XGBoost algorithm, we calculated the spectra slopes of short wavelengths between 215 and 240 nm (S215-240) and between 215 and 275 nm (S215-275). The results show that the S215-240 and S215-275 are ~2 times the widely used spectra slopes between 275 and 295 nm (S275-295) obtained by traditional method based on the raw spectra. Moreover, the S215-240 and S215-275 are more relavant with salinity for marine CDOM than S275-295, suggesting spectra slopes of shorter wavelengths might be the better proxies for marine CDOM than that of longer wavelengths.

Study on the interaction of two quinazoline derivatives as novel PI3K/mTOR dual inhibitors and anticancer agents to human serum albumin utilizing spectroscopy and docking.

Interactions of human serum albumin (HSA) with two structurally similar quinazoline derivatives, S1 and S2 , which are potential anticancer drugs acting on PI3K/mTOR targets, were investigated in vitro utilizing multiple spectroscopy as well as molecular docking. The fluorescence quenching study demonstrated that HSA fluorescence could be statically quenched by S1 and S2 through the formation of an HSA-drug complex. Furthermore, the details of the binding site number, binding constant, as well as the thermodynamic parameters, were estimated at 298, 303, and 310 K. The results revealed that hydrogen bond interactions, as well as van der Waals forces, were the predominant factors responsible for binding HSA to S1 or S2 . Synchronous fluorescence and ultraviolet (UV) absorption spectra suggested that S1 and S2 had little effect on the polarity of the microenvironment and conformation of HSA. Energy transfer from HSA to S1 or S2 most probably occurred. The docking study revealed that S1 and S2 were able to bind to the hydrophobic cavity that was located in the HSA subdomain IIA and formed varying numbers of hydrogen bonds with amino acid residues nearby. Due to the subtle difference in the chemical structure, the binding of S1 and S2 to HSA was slightly different.

TDDFT calculations of the PETN's ultraviolet absorption spectrum under the electric field loading.

The UV(ultraviolet) absorption spectrum of PETN under different electric field loading directions(X, Y, and Z) with the value of strength range from 0.001 a.u. to 0.006 a.u. was calculated with the TDDFT(Time-dependent density functional) in this work. With the increase of electric field strength, the absorbance of PETN in the ultraviolet band decreases. To explain the action mechanism of the electric field on PETN UV(ultraviolet) absorption spectrum, we analyzed and counted the contribution rate, oscillator strength, and vertical excitation energy of the main excitation process whose contribution rate to the UV absorption spectrum is greater than 10%. The contribution of PETN to the UV spectrum in all directions without an electric field was also listed to investigate the anisotropy of PETN in the excitation process under an electric field. The hole-electron analysis showed that the electric field will enhance the charge transfer characteristics in the excitation process of PETN. To investigate the anisotropy of the response under different electric field application directions, the contribution of the UV absorption spectrum in different directions was studied. Optimization and TDDFT calculation were performed at the level of M06-2X/def2-TZVP and PBE0/def2-TZVP respectively, with Gaussian09 program. The hole-electron analysis and UV absorption spectrum plotting were performed with Multiwfn3.8.

Effect of sodium bicarbonate and sodium chloride on protein conformation and gel properties of pork myofibrillar protein

To explore the potential of using sodium bicarbonate to take the place of sodium chloride, the changes in endogenous fluorescence, ultraviolet absorption spectrum, water holding capacity, gel properties and water distribution of pork myofibrillar protein were investigated. Because of the increase in pH and the exposure of more tryptophan and tyrosine residues with increasing sodium bicarbonate, the cooking yield and gel strength of pork myofibrillar protein significantly increased (P < 0.05), and centrifugal loss significantly decreased (P < 0.05). Meanwhile, the colour of the cooked pork myofibrillar protein was darker with increasing sodium bicarbonate, the bound water and immobile water were bound more tightly to the protein matrix, and the mobility of the water was lower, except for in the sample with 0.4 % sodium bicarbonate. Moreover, free water significantly increased (P < 0.05) when 0.4 % sodium bicarbonate was added, indicating that the mobility of the water was enhanced. Overall, the use of sodium bicarbonate could induce the protein conformation change, and improve the bond water content and texture properties of reduced-salt pork myofibrillar protein.

Ab Initio Calculations of XUV Ground and Excited States for First-Row Transition Metal Oxides

Transient X-ray spectroscopies have become ubiquitous in studying photoexcited dynamics in solar energy materials due to their sensitivity to carrier occupations and local chemical or structural dynamics. The interpretation of solid-state photoexcited dynamics, however, is complicated by the core–hole perturbation and the resulting many-body dynamics. Here, an ab initio, Bethe–Salpeter equation (BSE) approach is developed that can incorporate photoexcited state effects for solid-state materials. The extreme ultraviolet (XUV) absorption spectra for the ground, photoexcited, and thermally expanded states of first row transition metal oxides─TiO2, α-Cr2O3, β-MnO2, α-Fe2O3, Co3O4, NiO, CuO, and ZnO─are calculated to demonstrate the accuracy of this approach. The theory is used to decompose the core–valence excitons into the separate components of the X-ray transition Hamiltonian for each of the transition metal oxides investigated. The decomposition provides a physical intuition about the origins of XUV spectral features as well as how the spectra will change following photoexcitation. The method is easily generalized to other K, L, M, and N edges to provide a general approach for analyzing transient X-ray absorption or reflection data.

Multiple Chelation-Assisted Lithiation Improves the Performance of Phosphate-Modified LiNi0.8Co0.1Mn0.1O2

Phytic acid, the main phosphorus repository for plant seeds, is enriched with phosphate acidic sites that can easily chelate with transition metal ions. In this article, a phosphate-modified LiNi0.8Co0.1Mn0.1O2 (P-NCM) cathode material was synthesized using a Phytic acid-assisted lithiation process involving multiple chelation between phytic acid and metal hydroxides. Characterized by X-ray diffraction, Ar+ sputtering assisted X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, etc, it indicates that P-NCM indeed possesses the phosphorus dopant besides Li3PO4 coating. Through galvanostatic intermittent titration results, reflected electron energy loss spectra, and ultraviolet absorption spectra, it indicates that the optimal 0.2PA modified sample has a higher Li+ diffusion rate and electron conductivity, with an initial discharge capacity of 203.4 mAh g−1 and the retention of 92.4% after 100 cycles at 1 C and room temperature. In-situ XRD measurements indicate that the 0.2PA has fewer volume changes in the H2-H3 phase transition. Density Functional Theory calculations reveal that the phosphorus dopant probably occupies the tetrahedral interstice in the LiO6 layer, existing obvious charge transfers from the phosphorus dopant toward the neighboring atoms. This work illustrates the important role of phosphorus dopants in the improvement of the electrochemical properties of Ni-rich NCM cathode materials.

Quantitative analysis of SO2, NO2 and NO mixed gases based on ultraviolet absorption spectrum.

SO2, NO2 and NO are the main atmospheric pollutants produced by the combustion of fossil fuel. Detecting these gases is of great significance for atmospheric protection and the online concentration detection of pollutants. In this study, the concentration retrieval methods of NO, NO2 and SO2 and their mutual effects were studied in the wavelength range of 192.3-254.4 nm. In this band, NO, NO2 and SO2 have large absorption cross-sections; however, their spectrum superpositions were serious. A novel method was proposed to separate the superposed absorption spectra of NO and SO2 or NO2. The advantage of this method is that it can remove the influence of SO2 and NO2 on NO concentration retrieval. The fast Fourier transform (FFT) amplitude method was used to calculate the concentrations of SO2 and NO2, and the direct absorption spectroscopy method was used to calculate NO concentration. Via these methods, the gas concentrations of SO2, NO2 and NO can be calculated in ternary-gas mixtures. The experimental results show that these methods can effectively remove the mutual interferences between the concentration retrieval of NO, NO2 and SO2. The maximum absolute values of the relative deviations for the concentration retrieval of SO2, NO2 and NO in ternary-gas mixtures are 3.868%, 4.740% and 5.008%, respectively. These methods have high detection precision and good adaptability and are suitable for online flue detection equipment.

Quantitative prediction model for affinity of drug-target interactions based on molecular vibrations and overall system of ligand-receptor

Herein, surface-enhanced Raman scattering (SERS) and ultraviolet visible absorption spectrum in combination with fluorescence spectroscopy were jointly explored to investigate the binding interaction between Enrofloxacin (EFLX) with Bovine serum albumin (BSA) at a physiological condition. A facile SERS substrate based on the self-assembly of colloid silver on the modified TiN-Ag surface was obtained, an advanced SERS analysis method basing on this as-prepared substrate was established for sensitive and rapid detection of enrofloxacin, the most enhanced mode was that with certain motions perpendicular to the metal surface. In addition, the fluorescence and ultraviolet spectrum were allowed to found that enrofloxacin may bind to BSA site I via the carboxyl group with strong binding power.

Structural and Colloid Effects of Interaction between Shungite Carbon Nanoparticles and Linoleic Fatty Acid

Background: The effect of bionanointeractions on graphene-biomolecule nanohybrids is of great interest, since external influences on their structural and surface properties can significantly affect their biological activity. Introduction: The effects of the fatty acid binding with shungite carbon (ShC) nanoparticles on the stability of aqueous dispersions of ShC and the oxidation state of ShC (oxygen-containing groups) were studied using linoleic acid (LA) as an example. Method: The size and surface charge (ζ -potential) of the ShC-LA associates formed at various LA concentrations in the dispersion were estimated using the dynamic light scattering method and the ultraviolet (UV) absorption spectra of dispersions were taken. Result: The negative ShC charge becomes less negative upon LA binding, depending on LA concentration. The size of ShC upon functionalization by LA molecules does not depend on LA concentration, suggesting the predominance of surface rearrangement of NPs, rather than a change in their global structure. ShC - LA interaction is accompanied by an increase in absorption in the UV spectrum region of conjugated С=С bonds, the reduction of С=О groups, sp2 hybridization and bonds in the plane of graphene fragments, the basic structural units of ShC. Conclusion: The results are interpreted in terms of the surface structural effects of LA on ShC that affect variations of the colloid and redox characteristics of ShC in aqueous dispersion.

THE ROLE OF THE MIXING LIQUID IN THE PROCESSES OF HYDRATION AND HARDENING OF CEMENT STONE

The paper shows that the activation of the mixing fluid by an alternating electromagnetic field of a given signal shape with an energy even a billion times less than the thermal motion energy leads to an increase in the strength of the cement stone hardening structures. As follows from the ultraviolet absorption spectra of the mixing liquid, after repeated treatment with a magnetic field, an increase in the optical density of hydrogen bonds is observed. Thermophysical and acoustic methods have established the inhomogeneity of the temperature distribution at various points of a given volume of water and the formation of spatial structures on its surface at certain frequencies. A wide range of electrophysical methods shows the correlation of changes in the properties of water and the characteristics of the processes of hydration and structure formation of cement stone.

Nitrite Quantification by Second Derivative Chemometric Models Mitigates Natural Organic Matter Interferences under Chloraminated Drinking Water Distribution System Conditions

Nitrite (NO2−) production in chloraminated drinking water distribution systems (CDWDSs) is among the first bulk water indicators of a nitrification event and is typically quantified using ion chromatography (IC) or colorimetric techniques. NO2− can also be quantified using chemometric models (CMs) formulated using molar absorptivity (Ɛ) and/or ultraviolet absorbance (UVA) spectra, but concerns exist regarding their accuracy and generalizability because of varying source water natural organic matter (NOM), monochloramine (NH2Cl), bromide (Br−), and other species in CDWDSs. We demonstrate that the impact of NOM was mitigated in the second derivative molar absorptivity (Ɛ″) and UVA spectra (UVA″) between 200–300 nm and developed a generalizable CM for NO2− quantification. The Ɛ″+UVA″ CM was calibrated with daily NO2− measurements by IC from five biofilm annular reactor (BAR) tests with feedwater from Fayetteville, Arkansas, USA (FAY1, n = 275) and validated with eight BAR tests (n = 376) with another Fayetteville water (FAY2) and two waters from Dallas, Texas, USA (DAL1 and DAL2). The Ɛ″+UVA″ CM used Ɛ″ for NO2−, nitrate (NO3−), Br−, and NH2Cl at wavelengths of 213-, 225-, 229- and 253 nm, had an adjusted R2 of 0.992 for FAY1 and 0.987 for the other waters, and had a method detection limit (MDL) of 0.050 mg·L−1-N. NO2− challenge samples with three reconstituted NOM types and Br− indicated the Ɛ″+UVA″ CM was generalizable at NOM concentrations like those in the BAR tests (≤ 2.5 mg·L−1-C). The Ɛ″+UVA″ CM accurately simulated NO2− in field tests from two CDWDSs undergoing nitrification, including one with NOM at 3.5 mg·L−1-C, illustrating a practical application of the CM for identifying biological ammonia oxidation.

Trichromatic ratiometric fluorescent sensor based on machine learning and smartphone for visual and portable monitoring of tetracycline antibiotics

In this work, a tri-color ratiometric fluorescent optical device integrated with machine learning-assisted smartphones is designed for the visual monitoring of tetracycline antibiotics. The trichromatic sensing probe consists of blue emitting carbon dots (BCDs) at 420 nm, and red-emitting bovine serum albumin-protected copper nanoclusters (BSA-Cu NCs) at 635 nm, as well as an emission peak at 520 nm, rises in the presence of tetracycline antibiotics (TCs), therefore, a three emission system is formed. BCDs/BSA-Cu NCs present three emission responses to TCs, which are based on the internal filtering effect (IFE) and the sensitization mechanisms with BSA. The reaction mechanism was verified by density functional theory (DFT) and a series of characterizations, such as infrared spectrum, ultraviolet absorption spectrum, and fluorescence lifetime. Interestingly, the fluorescence intensity of BCDs was quenched by TCs, and due to the sensitization between BSA and TCs, a green fluorescence rose at 520 nm, while the peak of BSA-Cu NCs remained stable, resulting in a significant color shift from red to cyan. Therefore, the ratiometric fluorescence intensity of I(635+520)/I420 can be used to determine TCs, and the colors change can be used to identify the quantitative analysis. In addition, the deep learning of the YOLO v3 algorithm assists the integrated tri-color portable optical device of smartphones, which can realize the visual detection of TCs. In general, the sensing system has many advantages, such as good stability, specificity, and rich color changes, which provide help for the visual detection of tetracycline residues.

Imaging the Photodissociation Dynamics and Fragment Alignment of CH2BrI at 193 nm.

The photodissociation dynamics and photofragment alignment of bromoiodomethane (CH2BrI) have been studied at 193 nm using a double experimental and theoretical approach. In addition, the ultraviolet (UV)-vacuum ultraviolet (VUV) absorption spectrum of gas phase CH2BrI has been measured in the photon energy range of 5-11 eV using the VUV Fourier transform spectrometer (FTS) at the VUV beamline DESIRS of the synchrotron SOLEIL facility. The slice imaging technique in combination with resonance enhanced multiphoton ionization (REMPI) detection of the Br(2PJ) and I(2PJ) (with J = 3/2 and 1/2 for Br/I and Br*/I*, respectively) atomic photofragments have been used to produce experimental translational energy and angular distributions, which were analyzed to deliver, on one hand, the partitioning of the available energy among the different degrees-of-freedom of the photofragments and, on the other, the photofragment polarization in terms of aqk(p) alignment parameters. The experimental measurements were rationalized in terms of high-level ab initio calculations of vertical excitation energies, transition dipole moments and potential energy curves (PECs) along different reaction coordinates to provide a complete picture of the photodissociation dynamics. The results indicate that for excitation at 193 nm, prompt C-X cleavage (with X being either halogen atom, Br or I) competes with fast internal conversion and consequent stochastic dissociation in lower electronic states. In the case of the CH2Br + I(2P3/2)/I*(2P1/2) channels, the dynamics are greatly biased toward the stochastic dissociation process due to both the particular PECs landscape and the unfavored excitation of the CH2BrI ensemble with respect to the C-I molecular axis at this excitation energy. The ab initio PECs provide a tentative path for the fast dissociation process in either case. For the C-Br bond breakage, excitation to the 13A' electronic state and predissociation through the 11A'/11A″ or 12A'/12A″ states, leading to direct dissociation through the 10A'/9A″ states, appear as the most consistent dynamics. For the C-I channel, predissociation does not become a reliable possibility and a fast internal conversion may precede dissociation through the repulsive 6A'/6A″ and 4A'/4A″ states. The large content of rotational and vibrational excitation of the polyatomic cofragments is justified through the soft impulsive model and the geometrical changes produced along the dissociation pathway. Strikingly, the aqk(p) alignment parameters obtained for the Br(2P3/2) and I(2P3/2) photoproducts indicate that the rotational angular momentum of the CH2X (X = I or Br) cofragment appears highly constrained along the recoil direction. Finally, this work presents a highly plausible explanation for the branching ratio of secondary dissociation processes in the photodynamics of CH2BrI at 193 nm.

The excited states of azulene: A study of the vibrational energy levels for the lower ππ*-valence states by configuration interaction and density functional calculations, and theoretical studies of the Rydberg states.

A new vacuum ultraviolet absorption (VUV) spectrum of azulene vapor has been obtained by using a synchrotron radiation source. The onset of the ultraviolet spectrum, previously reported by Sidman et al., has been analyzed in detail by Franck-Condon (FC) and Herzberg-Teller (HT) methods. The photoelectron spectral profile identifies the 3px-Rydberg state 00 band to be 131cm-1 from the VUV maximum. Excited state energy levels were calculated by three independent methods: the wide scan VUV spectrum was correlated with symmetry adapted cluster configuration interaction calculations. The low energy portion of the spectrum was studied by both time dependent density functional theoretical methods (TDDFT) and multi-reference multi-root CI (MRD-CI). Equilibrium structures were determined for valence states at the TDDFT level. Rydberg states were determined by both TDDFT and MRD-CI. The FC + HT analyses were performed on the TDDFT wave-functions. The HT intensity profiles are generally low in intensity, relative to the FC ones; however, HT is dominant in the second singlet state (S2, 11A1). As a result, numerous non-symmetric modes, their overtones, and combination bands show considerable intensity in that band. Energies obtained from use of extremely diffuse s-, p-, d-, or f-character functions enabled realistic extrapolation to the IE1 for many Rydberg states (RS). The lowest RS (3b13s) based on IE2 lies at 4.804eV with a quantum defect of 0.714. Differentiation between valence and RS is readily made using the second moments of the charge distribution.