263 research outputs found
Rotational Spectroscopy of the 2,2,3,3,3‐Pentafluoropropanol⋅⋅⋅Water Complex: Conformations and Large Amplitude Motions
No full textRotational Spectrum and Molecular Structures of the Binary Aggregates of 1,1,1,3,3,3-Hexafluoro-2-propanol with Ne and Ar
No full text2,2,3,3,3-Pentafluoro-1-propanol and its dimer: structural diversity, conformational conversion, and tunnelling motion
No full textRotational spectra of 2,2,3,3,3-pentafluoro-1-propanol (PFP) were measured using cavity and chirped pulse Fourier transform microwave spectrometers. Of the nine possible PFP configurations which include four mirror-imaged pairs and an achiral conformer, the two most stable monomeric PFP imaged pairs, i.e., PFPG+g+/G−g− and PFPTg+/Tg− were observed and assigned, along with the 13C, 18O and deuterated isotopologues of PFPG+g+/G−g−. The rotational transitions of PFPTg+/Tg− exhibit large tunnelling splittings and were analyzed in detail. CREST, a recently developed conformational search tool that was used for systematic conformational searches of possible binary PFP conformers and the subsequent DFT calculations at the B3LYP-D3(BJ)/def2-QZVP level produced nearly 80 stable, binary PFP geometries, where ten of them are within a narrow energy window of ∼1 kJ mol−1, highlighting the structural diversity of the system. Rotational spectra of five (PFP)2 conformers were assigned and were identified as the five most stable binary conformers predicted. A closer examination reveals that the assigned binary conformers are made exclusively of the two most stable PFP monomeric subunits observed experimentally. A combined kinetic and thermodynamic model was proposed to explain the observation or non-observation of low energy conformers, and the analysis was further verified by the ‘argon test’. The non-covalent intermolecular interactions of PFP and its binary conformers are also discussed with the aid of quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses, as well as the effects of fluorination by comparing with 1-propanol and its dimers.This work was funded by the Natural Sciences and Engineering Research Council of Canada and the University of Alberta. A. I. acknowledge the support of a H. E. Gunning Research Fellowship, and a research award through the Mobility Program: Egonlabur 2020–2021, the University of the Basque Country UPV/EHU and a predoctoral fellowship from the Basque Government, Spain, respectively. S. O. thanks the Fonds der Chemischen Industrie for financial support.Peer reviewe
Higher-Energy Hexafluoroisopropanol···Water Isomer and Its Large Amplitude Motions: Rotational Spectra and DFT Calculations
No full textRobust Efficient Estimation of Semiparametric Covariate Models based on Minimum Hellinger Distance
No full textCovariate models, such as polynomial regression models, generalized linear models, and heteroscedastic models, are widely used in statistical applications. The importance of such models in statistical analysis is abundantly clear by the ever-increasing rate at which articles on covariate models are appearing in the statistical literature. Because of their flexibility, covariate models are increasingly being exploited as a convenient way to model data that consist of both a response variable and one or more covariate variables that affect the outcome of the response variable. This thesis investigates efficient and robust estimates for this class of models. For this purpose, we employ the minimum distance approach which in general is automatically robust with respect to the stability of the quantity being estimated. In particular, the minimum Hellinger distance estimation (MHDE) introduced by Beran (1977) for parametric models produces estimators that are asymptotically efficient at the model density and simultaneously possess excellent robustness properties. Wu and Karunamuni (2015) extended the idea and proposed the minimum profile Hellinger distance estimation (MPHDE) for semiparametric models of general form. In this thesis, we first construct an MPHDE for single-index models which are the most commonly used covariate models, prove its consistency, and examine its finite-sample performance and robustness properties via Monte Carlo simulation studies and real data analysis. We further extend the MPHDE to the general covariate models, in which we prove the consistency and asymptotic normality of the proposed MPHDE and a computing algorithm is developed to ease the computation of the estimate. Its finite-sample performance, including efficiency and robustness, are examined by simulation studies and real data applications
Rotational and vibrational spectroscopy of a weakly bound hexafluoroisopropanol⋯dinitrogen complex: 14 N hyperfine splittings, molecular geometry, and experimental benchmarks
No full textStructure and internal dynamics of hexafluoroisopropanol⋯N 2 were uncovered by rotational spectroscopy, aided by spin statistics analyses and ab initio calculations. The data from rotational and vibrational spectra serve as benchmarks for theory.The rotational spectrum of a weakly bound binary complex of hexafluoroisopropanol (HFIP) with molecular nitrogen was measured using chirped-pulse and cavity-based Fourier transform microwave spectrometers. In addition, its infrared spectrum was measured in the OH stretching region. An extensive conformational search identified multiple binding sites on HFIP, with the global minimum structure featuring a trans -HFIP conformation and nitrogen weakly bound at the acidic proton (H t N H ). Good agreement between the experimentally determined rotational constants and the relative intensity patterns of a -, b -, and c -type transitions with theoretical predictions conclusively identified the H t N H conformer. This assignment is further corroborated by an analysis of the 14 N nuclear quadrupole hyperfine structure. The non-equivalence of the two 14 N nuclei in H t N H is confirmed through a detailed molecular symmetry group analysis, as well as the 14 N nuclear quadrupole hyperfine analysis. Examination of the experimental nuclear quadrupole coupling constants offers additional insights into the orientation and large-amplitude vibrational motions of the N 2 subunit. Furthermore, the experimentally derived rotational constants and the OH stretching band position of the complex, compared with previously known values for the isolated monomer, serve as complementary benchmarks for evaluating the systematic quality of predictions from electronic structure calculations across several levels of theory. This combined examination of vibrational energy levels and structural parameters aids in distinguishing fortuitously accurate predictions of individual properties.Structure and internal dynamics of hexafluoroisopropanol⋯N 2 were uncovered by rotational spectroscopy, aided by spin statistics analyses and ab initio calculations. The data from rotational and vibrational spectra serve as benchmarks for theory.The rotational spectrum of a weakly bound binary complex of hexafluoroisopropanol (HFIP) with molecular nitrogen was measured using chirped-pulse and cavity-based Fourier transform microwave spectrometers. In addition, its infrared spectrum was measured in the OH stretching region. An extensive conformational search identified multiple binding sites on HFIP, with the global minimum structure featuring a trans -HFIP conformation and nitrogen weakly bound at the acidic proton (H t N H ). Good agreement between the experimentally determined rotational constants and the relative intensity patterns of a -, b -, and c -type transitions with theoretical predictions conclusively identified the H t N H conformer. This assignment is further corroborated by an analysis of the 14 N nuclear quadrupole hyperfine structure. The non-equivalence of the two 14 N nuclei in H t N H is confirmed through a detailed molecular symmetry group analysis, as well as the 14 N nuclear quadrupole hyperfine analysis. Examination of the experimental nuclear quadrupole coupling constants offers additional insights into the orientation and large-amplitude vibrational motions of the N 2 subunit. Furthermore, the experimentally derived rotational constants and the OH stretching band position of the complex, compared with previously known values for the isolated monomer, serve as complementary benchmarks for evaluating the systematic quality of predictions from electronic structure calculations across several levels of theory. This combined examination of vibrational energy levels and structural parameters aids in distinguishing fortuitously accurate predictions of individual properties.Natural Sciences and Engineering Research Council of Canada https://doi.org/10.13039/501100000038University of Alberta https://doi.org/10.13039/501100000190Canada Research Chairs https://doi.org/10.13039/501100001804Fonds der Chemischen Industrie https://doi.org/10.13039/10001899
Microwave synthesis of lithium cobalt oxide & iron-doped lithium cobalt oxide for oxygen evolution reaction
No full textOxygen evolution reaction (OER) plays a critical role in many advanced technologies for obtaining sustainable and clean energy, such as water splitting and CO2 reduction. However, current industry used precious metal-based OER catalysts (i.e. Ir, Ru) suffers from problems of low abundance and instability under high anodic potentials, which keeps these technologies far from large-scale applications. Recently, lithium cobalt oxide (LiCoO2) has been found as one of highly active and stable catalysts in OER, shows a potential to replace the precious metal. However, the most common used methods to synthesize LiCoO2 are based on traditional solid-state annealing, which has drawbacks in time/energy consuming and uncontrollable morphology. In this thesis, we developed a fast, simple, and cost-effective method to synthesize LiCoO2 taking advantage of the unique fast heating via microwave irradiation.
Chapter 1 includes a brief overview on oxygen evolution reaction and OER catalysts. The microwave heating mechanism will also be introduced.
In chapter 2, we designed a fast and pretreatment-free microwave-assisted method to synthesize LiCoO2 with small particle sizes. We found that the microwave process influences the crystal structures and the amount of Co3O4 impurities in the fabricated LiCoO2 particles. An optimal microwave irradiation process was established to eliminate all the Co3O4 impurities. The as-synthesized LiCoO2 with different structures as an electrochemical catalyst for oxygen evolution reaction in a water splitting setup to generate hydrogen was tested. The existence of Co3O4 impurities in the fabricated LiCoO2 particles negatively impacts on their OER performance. The LiCoO2 particles with minimal Co3O4 impurities exhibited a comparable performance with an overpotential of 430mV at 10mA/cm2 as those fabricated by previous reported approaches.
In chapter 3, using the microwave irradiation method developed in chapter 2, we successfully doped Fe into the LiCoO2 frameworks. OER performance showed an obvious increase upon Fe doping. LiCoO2 with 20% Fe exhibited the best OER activity with an overpotential (η) of 370mV at 10mA/cm2, which deceased 60 mV compared to that of the undoped LiCoO2. Characterization of these Fe doped LiCoO2 via X-ray photoemission spectroscopy (XPS) demonstrated the electronic interaction between Fe and Co, which pushed the Co to a higher oxidation state of Co4+ from Co3+ in the undoped LiCoO2.M.S.Includes bibliographical referencesby Bowei L
Brushing, a simple way to fabricate SERS active paper substrates
Get PDFA simple and facile method has been demonstrated to fabricate low-cost surface enhanced Raman scattering (SERS) active microfluidic paper chips using a painting brush. This strategy solves the problem of mass production of highly reproducible SERS substrates without complicated or bulky micro-or nanofabrication instruments. Rhodamine 6G (R6G) was chosen as a probe molecule to evaluate the performance of the SERS active chip. To further demonstrate the possibility of this method's potential application in environmental monitoring, trace malachite green (MG) was successfully analyzed on this chip. The performance of our chips was desirable. The paper substrates with silver nanoparticles deposited by brush were found to be cost-efficient and highly sensitive (LOD for R6G and MG are 1 nM and 10 nM, respectively), and have good reproducibility (similar to 15% relative standard deviation)
Large Amplitude Motions In 2,2,3,3,3-pentafluoropropanol And Its Binary Water Complex
Get PDF2,2,3,3,3-pentafluoropropanol (PFP) is an important solvent for organic syntheses. It is also considered to be a green-house gas pollutant because it is radiatively active in the mid-infrared region. Understanding properties of PFP and its hydrogen bonding interactions with water in the gas phase may help to develop more realistic estimate of its effects because of the abundance of water in the atmosphere. In the current study, we apply both rotational spectroscopy and ab initio calculations to characterize large amplitude motions in PFP and its water complex and also hydrogen bonding interactions between PFP with water. Their rotational spectra were recorded using a cavity-based and a chirped pulse Fourier transform microwave spectrometers. Two most stable PFP conformers, Pg+g+ and Ptg+ were identified. The rotational transitions of the latter exhibit tunneling splittings. Two PFP-H2O conformers were identified and both of them show tunneling splittings. Deuterated species of the water complex were also investigated to assist the identification of the tunneling paths, in addition to the theoretical calculations. The large amplitude motions responsible for these splittings will be discussed.Made available in DSpace on 2021-09-24T21:09:25Z (GMT). No. of bitstreams: 2
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Large amplitude motions in 2,2,3,3,3-pentafluoropropanol and its binary water complex
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Previous issue date: 242,2,3,3,3-pentafluoropropanol (PFP) is an important solvent for organic syntheses. It is also considered to be a greenhouse gas pollutant because it is radiatively active in the mid-infrared region. Understanding properties of PFP and its hydrogen bonding interactions with water in the gas phase may help to develop more realistic estimate of its effects because of the abundance of water in the atmosphere. In the current study, we apply both rotational spectroscopy and ab initio calculations to characterize large amplitude motions in PFP and its water complex and also hydrogen bonding interactions between PFP with water. Their rotational spectra were recorded using a cavity-based and a chirped pulse Fourier transform microwave spectrometers. Two most stable PFP conformers, Pg+g+ and Ptg+ were identified. The rotational transitions of the latter exhibit tunneling splittings. Two PFP···H2O conformers were identified and both of them show tunneling splittings. Deuterated species of the water complex were also investigated to assist the identification of the tunneling paths, in addition to the theoretical calculations. The large amplitude motions responsible for these splittings will be discussed
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