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A Quantum Chemical Study of Germanium-Substituent Bonding in Complex Compounds of Germanium
摘要： Spatial and electronic structures of six-coordinated germanium compounds are calculated within МР2 and AIM methods using PC GAMESS-Firefly, MORPHY, and AIMALL software packages. Main topological characteristics of germanium-substituent bonds are determined in these molecules.
关键词： AIM method,quantum chemistry
更新于2025-09-23 15:22:29
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High Resolution Laser Spectroscopic Survey of the H <sup>3</sup> ?￡ <sub/>u</sub><sup>-</sup> - X <sup>3</sup> ?￡ <sub/>g</sub><sup>-</sup> Electronic Transition of Si <sub/>2</sub>
摘要： Rotationally resolved spectra of the H3Σ?u - X3Σ?g electronic transition bands of Si2 have been experimentally studied using laser induced fluorescence in the 380 - 520 nm range. Si2 molecules are produced in a supersonically expanding planar plasma by discharging a silane/argon gas mixture. In total 44 bands belonging to the H3Σ?u - X3Σ?g electronic transition system of the most abundant isotopologue 28Si2 are experimentally recorded. With a spectral resolution ～ 0.04 cm?1, the triplet spin-splitting structures in individual rotational transition lines are fully resolved. Detailed analyses on the high resolution spectra have yielded an accurate determination of spectroscopic constants for both X3Σ?g and H3Σ?u states. The spin-spin interaction constants for the two triplet states are found to be comparable (λ ～ 1.5 cm?1), which may originate from the 3p atomic orbital interaction in the triplet Si2 molecule. The measured isotopologue spectra of 29Si28Si and 30Si28Si indicate that the H3Σ?u - X3Σ?g transition system of 29Si28Si and 30Si28Si can be reasonably reproduced by the isotope mass-scaling rule. Spectroscopic parameters including the Franck-Condon factors, the Einstein coefficients, and the oscillator strengths, are also determined from the experimental results and the RKR calculations. The agreement between the experimentally measured and calculated dispersed fluorescence spectra indicates that the RKR calculations with the molecular constants determined in this work can accurately reproduce the diatomic potentials of both states. These molecular data providing a benchmark in high-level theoretical studies on Si2 and likely other small silicon clusters.
关键词： Molecular Structure,Quantum Chemistry,Spectroscopy
更新于2025-09-23 15:21:01
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Tuning Hydrogenated Si, Ge, and SiGe Nanocluster Properties Using Theoretical Calculations and a Machine Learning Approach
摘要： There are limited studies available that predict the properties of hydrogenated silicon-germanium (SiGe) clusters. For this purpose, we conducted a computational study of 46 hydrogenated SiGe clusters (SixGeyHz, 1<X+Y≤6) to predict the structural, thermochemical, and electronic properties. The optimized geometries of the SixGeyHz clusters were investigated using quantum chemical calculations and statistical thermodynamics. The clusters contained 6 to 9 fused Si-Si, Ge-Ge, or Si-Ge bonds, i.e., bonds participating in more than one 3- to 4-membered rings, and di?erent degrees of hydrogenation, i.e., the ratio of hydrogen to Si/Ge atoms varied depending on cluster size and degree of multifunctionality. Our studies have established trends in standard enthalpy of formation, standard entropy, and constant pressure heat capacity as a function of cluster composition and structure. A novel bond additivity correction model for SiGe chemistry was regressed from experimental data on 7 acyclic Si/Ge/SiGe species to improve the accuracy of the standard enthalpy of formation predictions. Electronic properties were investigated by analysis of the HOMO–LUMO energy gap to study the effect of elemental composition on the electronic stability of SixGeyHz clusters. These properties will be discussed in the context of tailored nanomaterials design and generalized using a machine learning approach.
关键词： Theoretical Calculations,SiGe Nanocluster,Ge,Machine Learning,Hydrogenated Si,Quantum Chemistry,Spectroscopy,Molecular Structure
更新于2025-09-23 15:21:01
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Energy Landscapes in Photochemical Dissociation of Small Peroxides
摘要： Organic peroxides are known to have important roles in many chemical and biochemical processes such as intermediates in the oxidation of various hydrocarbons, as initiators of free-radical polymerization and cross-linking agents, etc. Consequently, the study of the organic peroxides and their radicals are of fundamental interest and importance. Although several reaction pathways after dissociation of organic peroxides have been successfully identified using time-resolved optical absorption spectroscopy, interpretation of the data can be complicated due to spectral overlap of parent molecules, intermediates, and products. Therefore, a reliable theoretical framework is necessary in case of complex or less studied systems. In this study, we investigated the plausible thermal dissociation pathways of diethyl peroxide, di-tert butyl peroxide and dicumyl peroxide by density functional theory with M06-2X hybrid functional and compare its results to coupled cluster single double and perturbative triple, CCSD(T), level energies. Our results indicate that methyl radical elimination is the main dissociation mechanism for all the studied peroxides after O-O bond cleavage which has been also observed in experiments. The resulted relative energies of M06-2X functional were found to have reasonable accuracy in comparison with CCSD(T) method. We also show that time-dependent density functional theory (TD-DFT) with M06-2X functional provides a suitable guide for interpretation of time-resolved optical absorption spectra of peroxides. The experimental transient absorption spectra of dicumyl peroxide are interpreted using the theoretically predicted pathways and transient radical species. Both results agree within experimental resolution and accuracy. We propose that the traditionally assigned visible absorption is not due to the cumuloxyl radical and the photodissociation of dicumyl peroxide involves other pathways with extremely short lived radicals.
关键词： Molecular Structure,Spectroscopy,Quantum Chemistry
更新于2025-09-19 17:15:36
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IR Cavity Ringdown Spectroscopy and Density Functional Theory for Jet-Cooled Pyrrolea??Cyclopentanone Binary Clusters: Effect of Pseudorotation on Na??H?·?·?·Oa??C Hydrogen Bonds
摘要： The geometry and energetics of the N-H…O=C hydrogen bond (H-bond) are important to understand the stability and flexibility of biomolecules, such as protein and DNA. Jet-cooled pyrrole-cyclopentanone (Py-Cp) binary clusters are appropriate models to investigate the N-H…O=C H-bond from a microscopic point of view. In this study, NH stretching vibrations of the Py-Cp binary clusters were observed by IR cavity ringdown spectroscopy. Furthermore, density functional theory calculations revealed geometric structures, harmonic vibrations, intermolecular energies, and donor-acceptor interactions for various sizes of binary clusters. The IR spectra of the Py-Cp binary clusters were measured under various conditions of the vapor pressures of Py and Cp in He buffer gas for a supersonic expansion. The dependence of the IR band intensities on the vapor pressure provides vibrational assignments of the NH stretching vibrations, which were reproduced by calculated frequencies of Py1-Cp1, Py1-Cp2, and Py2-Cp1. An admixture of Ar in He buffer gas for a supersonic expansion was also applied to produce Py1-Cp2 in order to differentiate several NH stretches of isomeric structures due to the pseudorotation of Cp molecules. Py1-Cp1 is formed by the N-H…O=C H-bond. Py1-Cp2 has a cyclic structure that is formed by the N-H…O=C H-bond and stacking interactions among Py and two Cp molecules. Py2-Cp1 also has a cyclic structure that is formed by not only the N-H…O=C H-bond, but also a N-H…π H-bond between two Py molecules and a stacking interaction between Py and Cp. A comparison of the H-bond geometries between Py2-Cp1 and the corresponding pyrrole-acetone binary cluster reveals that the stacking interaction between Py and Cp strengthens the N-H…O=C and N-H…π H-bonds through a cooperative effect.
关键词： Density Functional Theory,Cyclopentanone,Spectroscopy,Quantum Chemistry,Pyrrole,IR Cavity Ringdown Spectroscopy,Hydrogen Bonds,Molecular Structure,Pseudorotation
更新于2025-09-19 17:13:59
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Study on light aging of anhydride-cured epoxy resin used for RGB LED packaging material
摘要： RGB LED is widely used in white light illumination and display fields due to its high luminous efficiency and full color display. However, the color drift will occur when RGB LED is used for a long time. In this paper, the luminous performance of RGB LED encapsulated by epoxy materials during longtime lighting and the aging mechanism of methyl hexahydrophthalic anhydride (MHHPA) cured diglycidyl ether of bisphenol-A (DGEBA) were studied by Array spectrometer, ATR-FTIR, XPS and quantum-chemistry calculation. Firstly, the analysis of the lumen maintenance and forward voltage of RGB LED lamps showed, the color drift might be attributed to the degradation of its epoxy materials caused by blue light. FTIR Spectroscopy showed that the aging of packaging materials mainly occurred on the surface of blue LED lamps, where active hydrogen of secondary and tertiary carbon might be oxidized to carbonyl groups due to O2 or peroxy groups in the air. And the aging of epoxy materials also might include the chain scission or the rearrangement reactions of C-O-Ph. XPS results further manifested the decrease of C-C group and increase of C-O and C=O group were mainly caused by the chain scission of C-C, C-O-Ph or the ester groups and the oxidation of active hydrogen. And several possible aging reactions were given from the analysis of ATR-FTIR and XPS characterization. The results of quantum-chemistry calculation indicated that C-O bond in C-O-Ph of DGEBA/MHHPA epoxy system was more easily to be broken down during blue light aging, which further verified the results of IR and XPS characterization.
关键词： quantum-chemistry calculation,epoxy resin,light aging,RGB LED
更新于2025-09-16 10:30:52
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N719 Derivatives for Application in a Dye-Sensitized Solar Cell (DSSC): A Theoretical Study
摘要： The primary goal of this investigation is to analyze the influence of the chemical modifications on the electronic structures of N719 derivatives for their use in Dye-Sensitized Solar Cells (DSSC), by employing Density Functional Theory (DFT). UV-Visible spectra indicate that the electronic configurations are essential to study the absorption of solar irradiation and to analyze the charge transport mechanism between the Electron Transport Layer (ETL), the electrolyte, and the dye. Open and closed-shell electronic configurations are related to the absorption and the excitation energies of the dye. According to the results reported here, it is possible to say that the best candidates are N719, N719-2, N719-7, and N719-8 (neutral and di-anionic). They may be used as useful dye sensitizers due to their bandgap and band alignment with the ETL, which contributes to having an effective charge transport during the functioning of the solar device. Another parameter that is reported in this investigation is the Light-Harvesting Efficiency (LHE) for all studied systems. This could help to improve the performance of the device since there is an increment in the generation of charge carriers. These results could be useful as a guide for experimental investigations on chemical modifications of these sensitizers.
关键词： UV-Visible Spectra,Light-Harvesting Efficiency,Molecular Structure,Spectroscopy,DFT,N719 Derivatives,Theoretical Study,Quantum Chemistry,Density Functional Theory,DSSC,Dye-Sensitized Solar Cell,LHE
更新于2025-09-12 10:27:22
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Revealing Long-Range Substituent Effects in the Laser-Induced Fluorescence and Dispersed Fluorescence Spectra of Jet-Cooled CH <sub/><i>x</i> </sub> F <sub/> 3– <i>x</i> </sub> CH <sub/>2</sub> O ( <i>x</i> = 1, 2, 3) Radicals
摘要： The B?←X? laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the atmospherically important β-monofluoro ethoxy (MFEO), β,β-difluoro ethoxy (DFEO), and β,β,β-trifluoro ethoxy (TFEO) radicals were recorded with vibronic resolution under jet-cooled conditions. To simulate the spectra, Franck-Condon factors were obtained from quantum chemical computations carried out at the CAM-B3LYP/6-311++G(d,p) level of theory. The simulations reproduce well both the LIF and DF spectra. Both conformers (G and T) of MFEO and one (G) of the two conformers of DFEO contribute to the LIF spectrum. A comparison between the experimental and calculated spectra confirms the expected long-range field effects of the CHxF3?x group on electronic transition energies and bond strengths, especially in the excited electronic (B?) state. Although TFEO has only one conformer, its LIF spectrum is highly congested, which is attributed to the interaction between CO stretch and the ?CF3 internal rotation.
关键词： Laser-Induced Fluorescence,Molecular Structure,Spectroscopy,Quantum Chemistry,Fluoroethoxy Radicals,Jet-cooled,Dispersed Fluorescence
更新于2025-09-12 10:27:22
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Temperature Dependence in the NEXAFS Spectra of <i>n</i> -Alkanes
摘要： The Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of orthorhombic single crystals of n-octacosane (n-C28H58), recorded at room temperature (298 K) and at cryogenic temperatures (93 K), show distinct differences. The characteristic carbon 1s → σ*C-H band in the NEXAFS spectrum of n-C28H58 is broader and has a lower energy onset in its room temperature spectrum than in its NEXAFS spectrum recorded at cryogenic temperatures. Density functional theory simulations show that nuclear motion and molecular disorder contribute to the observed spectral broadness and are the origin of the low-energy onset of the C-H band in the room temperature spectrum.
关键词： Temperature Dependence,Quantum Chemistry,n-Alkanes,NEXAFS,Molecular Structure,Spectroscopy
更新于2025-09-11 14:15:04
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Approximating vibronic spectroscopy with imperfect quantum optics
摘要： We study the impact of experimental imperfections on a recently proposed protocol for performing quantum simulations of vibronic spectroscopy. Specifically, we propose a method for quantifying the impact of these imperfections, optimizing an experiment to account for them, and benchmarking the results against a classical simulation method. We illustrate our findings using a proof of principle experimental simulation of part of the vibronic spectrum of tropolone. Our findings will inform the design of future experiments aiming to simulate the spectra of large molecules beyond the reach of current classical computers.
关键词： quantum optics,boson sampling,squeezed light,quantum simulation,vibronic spectroscopy,quantum chemistry
更新于2025-09-10 09:29:36