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Mass separated particle flux from a laser-ablation metal cluster source
摘要： Flux waveforms of aluminum cluster beams supplied from a laser-ablation cluster source were precisely investigated under various source conditions such as background pressure, ablation laser intensity, and nozzle structure. A time-of-flight mass spectroscopy revealed that aluminum clusters with sizes up to 200 were generated and the amount of the clusters could be maximized by choosing a proper background pressure (～2 MPa) and an ablation laser fluence (～40 mJ/cm2). Flux waveforms of clusters having specific sizes were carefully reconstructed from the observed mass spectra. It is found that the pulse widths of the aluminum cluster beams were typically about 100 μs and much smaller than that of the monoatomic aluminum beam, indicating that the cluster formation was limited in a relatively small volume in the laser-ablated vapor. Introducing a conical nozzle having a large open angle was also found to enhance the cluster beam velocity and reduce its pulse width. A velocity measurement of particles in the cluster beam was conducted to examine the velocity spread of the supplied clusters. We found that the aluminum clusters were continuously released from the source for about 100 μs and this release time mainly determined the pulse width of the cluster beam, suggesting that controlling the behavior of an ablated vapor plume in the waiting room of the cluster source holds the key to drastically improving the cluster beam flux.
关键词： mass spectrometry,laser ablation,molecular beam,Cluster
更新于2025-09-12 10:27:22
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Infrared photodissociation spectroscopy of di-manganese oxide cluster cations
摘要： Infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional calculations have been employed to elucidate the geometric structure of a series of di-manganese oxide clusters Mn2Ox+ (x = 4–7). The theoretical exploration predicts that all investigated clusters contain a rhombus-like Mn2O2 core with up to four, terminally bound, oxygen atoms. The short Mn–O bond length of the terminal oxygen atoms of ～1.58 ? indicates triple bond character instead of oxyl radical formation. However, the IR-MPD spectra reveal that higher energy isomers with up to two O2 molecules η2-coordinated to the cluster core can be kinetically trapped under the given experimental conditions. In these complexes, all O2 units are activated to superoxide species. The sequential increase of the oxygen content in the cluster allows for a controlled increase of the positive charge localized on the Mn atoms reaching a maximum for Mn2O7+.
关键词： superoxide species,density functional theory,di-manganese oxide cluster cations,IR-MPD spectroscopy,Infrared photodissociation spectroscopy
更新于2025-09-12 10:27:22
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Polarized Single-Particle Quantum Dot Emitters through Programmable Cluster Assembly
摘要： Although fluorescence and lifetimes of nanoscale emitters can be manipulated by plasmonic materials, it is harder to control polarization due to strict requirements on emitter environments. An ability to engineer 3D nano-architectures with nanoscale precision is needed for controlled polarization of nanoscale emitters. Here, we show that prescribed 3D hetero-cluster architectures with polarized emission can be successfully assembled from nanoscale fluorescent emitters and metallic nanoparticles using DNA-based self-assembly methods. An octahedral DNA origami frame serves as a programmable scaffold for heterogeneous nanoparticle assembly into prescribed clusters. Internal space and external connections of the frames are programmed to coordinate spherical quantum dots (QDs) and gold nanoparticles (AuNPs) into hetero-cluster architectures through site-specific DNA encodings. We demonstrate and characterize assembly of these architectures using in-situ and ex-situ structural methods. These cluster nanodevices exhibit polarized light emission with a plasmon-induced dipole along the QD-AuNP nanocluster axis, as observed by single-cluster optical probing. Moreover, emittance properties can be tuned via cluster design. Through a systematic study, we analyzed and established the correlation between cluster architecture, cluster orientation and polarized emission at a single-emitter level. Excellent correspondence between the optical behavior of these clusters and theoretical predictions was observed. This approach provides the basis for rational creation of single-emitter 3D nanodevices with controllable polarization output using a highly customizable DNA assembly platform.
关键词： DNA nanotechnology,polarization,fluorescence,quantum dots,nanoparticles cluster,self-assembly
更新于2025-09-12 10:27:22
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Lanczos-based equation-of-motion coupled-cluster singles-and-doubles approach to the total photoionization cross section of valence excited states
摘要： Excitation energies and oscillator strengths of the first two electronically excited states of helium, water, sulfur dioxide, molecular nitrogen, and carbon monoxide were obtained from an asymmetric-Lanczos-based formulation of the equation-of-motion coupled cluster singles and doubles approach. The total photoionization cross sections were generated by two different methodologies: an analytic continuation procedure based on the Padé approximants and the Stieltjes imaging technique. The results are compared with theoretical photoionization cross sections from algebraic diagrammatic construction [ADC(2)] and ADC(2)-x calculations [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] and with available experimental data.
关键词： Stieltjes imaging technique,coupled-cluster singles-and-doubles,photoionization cross section,Lanczos-based equation-of-motion,valence excited states,Padé approximants
更新于2025-09-12 10:27:22
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A general time-domain formulation of equation-of-motion coupled-cluster theory for linear spectroscopy
摘要： A time-dependent (TD) formulation of equation-of-motion (EOM) coupled-cluster (CC) theory is developed, which, unlike other similar TD-EOM-CC approaches [D. R. Nascimento and A. E. DePrince III, J. Chem. Theory Comput. 12, 5834–5840 (2016)], can be applied to any type of linear electronic spectroscopy. The TD-EOM-CC method is formally equivalent to the standard frequency-domain formulation of EOM-CC theory, with a potential computational advantage of a comparatively low memory footprint. This general TD-EOM-CC framework is applied to the linear absorption and electric circular dichroism spectra of several small oxirane derivatives.
关键词： electronic circular dichroism,linear spectroscopy,equation-of-motion,time-dependent,coupled-cluster theory
更新于2025-09-12 10:27:22
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Quantitative Analysis of Twelve Active Components Combined With Chromatographic Fingerprint for Comprehensive Evaluation of Qinma Prescription by Ultra-Performance Liquid Chromatography Coupled With Diode Array Detection
摘要： A combination method of ultra-performance liquid chromatography (UPLC) coupled with diode array detection has been developed for quality evaluation of Qinma prescription (QMP), based on chromatographic fingerprint technology with the similarity analysis (SA) and the quantitative analysis of 12 components by hierarchical cluster analysis (HCA). The established method has been validated by linearity, precision, repeatability, stability and recovery tests. The UPLC fingerprints with 17 common peaks of 5 QMP samples prepared by different extraction methods including water decoction extraction, water extraction-ethanol precipitation method, ethanol reflux extraction, ethanol extraction-water precipitation method and methanol ultrasonic extraction were obtained, and the SA results indicated that similarity index was greatly influenced by the large peak. The similarity index ranged from 0.816 to 0.999 basing on 17 peaks, which has been decreased to 0.683–0.999 basing on 16 peaks without the large peak of baicalin (BA). The results of simultaneous quantification of 12 components in these 5 QMP samples proved that BA, gallic acid (GA), wogonoside (WOG) and gentiopicroside (GEN) were the major ingredients in QMP with high contents >1.44 (mg/g), indicating that ethanol reflux was the most effective extraction method. Integrating fingerprint analysis, simultaneous determination and HCA, the established method is rapid, sensitive, accurate and readily applicable. All the results indicated that the combination method can control the quality of QMP and its related traditional Chinese medicinal compounds more comprehensively and scientifically.
关键词： quantitative analysis,Qinma prescription,similarity analysis,diode array detection,UPLC,hierarchical cluster analysis,chromatographic fingerprint
更新于2025-09-12 10:27:22
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A silver cluster‐assembled material (SCAM) showing luminescent mechanochromism and thermochromism
摘要： A silver cluster-assembled material (SCAM) showing luminescent mechanochromism and thermochromism
关键词： luminescent mechanochromism,Silver cluster,luminescent thermochromism,cluster-assembled material
更新于2025-09-11 14:15:04
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Controlled Joint Remote Preparation of a Six-Qubit Cluster-Type State by Using GHZ States
摘要： A scheme for the controlled joint remote preparation of an arbitrary six-qubit cluster-type state by using only two sets of five-qubit GHZ states as quantum channel is proposed. In our scheme, Alice firstly performs two sets of two-qubit projective measurement according to the real coefficients and the complex coefficients of the desired six-qubit cluster-type state. Then, the controller Charlie must apply another two-qubit projective measurement according to the Alice’s measurement result. Finally, Bob can obtain the desired six-qubit cluster-type state according to an appropriate unitary operation. Our scheme can achieve unit success probability.
关键词： Six-qubit cluster-type state,Quantum information,Controlled joint remote preparation
更新于2025-09-11 14:15:04
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Nd3+ Cluster Adjustment in Nd3+:CaNb2O6 by Co-doping La3+ Buffers for Improvement of Fundamental and Self-stimulated Raman Scattering Laser Operation: A Study Case from the Perspective of Defect Chemistry
摘要： The fluorescence quenching caused by Nd3+ clusters in Nd3+ doped crystal even at low Nd3+ concentration has restrained the performance of Nd3+ laser. In this work, Nd3+:CaNb2O6 and Nd3+:La3+:CaNb2O6 single crystals have been grown by the Czochralski method. RE3+ (RE3+=Nd3+, La3+) ion incorporation mechanisms, the formation of Nd3+ clusters, and the feasibility of La3+ ions as buffers in RE3+:CaNb2O6 crystal have been demonstrated and assessed by atomistic simulation methods. The spectral and laser properties of the Nd3+:CaNb2O6 and Nd3+:La3+:CaNb2O6 have been measured. All the results indicate the Nd3+ dimers with distances between Nd3+ close to the critical interaction distance have formed in the Nd3+:CaNb2O6 and the La3+ ions as buffers can alleviate the interaction of Nd3+ effectively in the Nd3+:La3+:CaNb2O6 as expected. Benefitting from the introducing of La3+ buffers, about 2.6 W fundament laser with slope efficiency of 36.5% and about 310 mW self-stimulated Raman scattering laser with conversion and slope efficiencies of 8.3% and 9.5%, respectively, which are superior to those of the Nd3+:CaNb2O6, have been achieved in the Nd3+:La3+:CaNb2O6.
关键词： laser,buffers ions,cluster adjustment,defect chemistry
更新于2025-09-11 14:15:04
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Equation of motion coupled-cluster for core excitation spectra: Two complementary approaches
摘要： This paper presents core excitation spectra from coupled-cluster (CC) theory obtained from both a time-independent and a new time-dependent formalism. The conventional time-independent CC formulation for excited states is the equation-of-motion (EOM-CC) method whose eigenvalues and eigenvectors describe the core excited states. An alternative computational procedure is offered by a time-dependent CC description. In that case, the dipole transition operator is expressed in the CC effective Hamiltonian form and propagated with respect to time. The absorption spectrum is obtained from the CC dipole autocorrelation function via a Fourier transformation. Comparisons are made among the time-dependent results obtained from second-order perturbation theory, to coupled cluster doubles and their linearized forms (CCD and LCCD), to CC singles and doubles (CCSD) and the linearized form (LCCSD). In the time-independent case, considerations of triples (EOM-CCSDT) and quadruples (EOM-CCSDTQ) are used to approach sub-electron volt accuracy. A particular target is the allyl radical, as an example of an open-shell molecule. As the results have to ultimately be the same, the two procedures offer a complementary approach toward analyzing experimental results.
关键词： time-independent formalism,time-dependent formalism,TD-EOM-CC,open-shell molecule,core excitation spectra,allyl radical,coupled-cluster theory,EOM-CC
更新于2025-09-11 14:15:04