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Ultrafast Chemical Reactions Probed by Time-Resolved Vibrational Spectroscopy
No full textA chemical reaction refers a series of atomic rearrangements between the reactant and product molecules, where the rearrangements of single chemical bonds occur on the ultrafast time scales of femtosecond and picoseconds. The chemical reactions are generally described by the energy difference between the reactant and products, activation barriers, reaction rates, etc. The reaction rates of a certain chemical reaction can be obtained by experimentally observe the concentration changes of reactant or product molecules. In order to measure the reaction rates of the ultrafast chemical reactions such as intramolecular proton transfer, ultrafast spectroscopic methods are inevitable where ultrashort laser pulses initiate the chemical reactions in the excited state and time-resolved spectroscopy measures the spontaneous concentration changes of reactants and/or products. The reaction dynamics study by the time-resolved spectroscopy would be beneficial in many important applications including artificial photosynthesis, dye-sensitized solar cell, or molecular optoelectronics. Simple photochemical reactions of excited state proton transfers and photoinduced charge transfers with subsequent structural changes in the electron donor or acceptor groups are considered as one of the fundamental processes in many chemical and biological systems. Therefore, the excited-state reaction dynamics probed by time-resolved spectroscopic measurements can be used to understand the ultrafast bond breaking and formation of reactant and product molecules, or the or the instantaneous structural changes accompanying various excited state photophysical processes.
In this thesis, transient absorption spectroscopy and femtosecond stimulated Raman spectroscopy (FSRS) has been adopted as the time-resolved electronic and vibrational probes, respectively. Time-resolved electronic and vibrational probes would be complementary to each other in analyzing the ultrafast photophysical and photochemical processes in the excited state.
The structural changes of 1,2-dihydroxyanthraquinone (alizarin) in dimethyl sulfoxide (DMSO) solution upon the excited-state intramolecular proton transfer (ESIPT) reaction have been studied by FSRS measurements. Previous time-resolved electronic measurements may provide the detailed excited-state dynamics upon the proton transfer. However, the detailed structural changes of alizarin or related molecules upon the ESIPT has not been reported. The ESIPT dynamics of alizarin of 70-80 fs has been observed from the vibrational modes of ν(C═C) and ν(C═O) in the singlet excited state, where the population changes and opposite peak shifts of these modes occurring with the common 70-80 fs time constant are compatible to the proposed transition state of six-membered ring structure with intramolecular hydrogen bonding between the carbonyl and adjacent hydroxyl group.
The ESIPT dynamics of alizarin has been updated by improving the temporal resolution of FSRS measurements with the pulse compression of actinic pump. The vibrational probe of ν(C═C) and ν(C═O) modes in the excited state have provided more detailed ESIPT dynamics (110 fs) of alizarin with the population transfer between the locally-excited (LE) and proton-transferred state, and the coherent oscillation signals in these vibrational probes show that the reaction coordinate of the ESIPT reaction is strongly coupled to several low-frequency vibrational modes of intramolecular hydrogen bonding. The solvent vibrational modes of DMSO, ν(S=O) and ν(CSC) are strongly changed upon the ESIPT of the solute alizarin. Although the vibrational modes of DMSO are inseparable from the nonlinear cross-phase modulation and long-lasting hot ground state Raman signals, the ν(S=O) and ν(CSC) modes of DMSO shows instantaneous (60-120 fs) increase in the “free (isolated)” or “aggregated (dimer)” bands indicating the solvation changes of DMSO upon the ESIPT of alizarin. The solvent vibrational modes of DMSO, ν(S=O) and ν(CSC), may “probe” the ultrafast chemical reactions of the solute indirectly since these modes are very sensitive to the instantaneous solvation changes resulting from the structural changes of the solute.
The photoinduced charge transfer dynamics of curcumin in DMSO solution has also been investigated by FSRS measurements. Curcumin is one of the well-known antioxidants, and shows ultrafast intramolecular charge transfer (ICT) in the excited stat, where the excited state lifetime and fluorescence quantum yield are strongly dependent on solvent polarity and hydrogen bonding with solvent. The vibrational modes of curcumin in the LE and charge-transferred (CT) states are separately observed from the FSRS measurements, where an ultrafast ICT (0.6-0.8 ps) and subsequent vibrational relaxation (6-9 ps) dynamics in the CT state have been retrieved. The ground-state vibrational modes of curcumin, ν8a and ν(C=C,C=O) and the solvent vibrational modes of DMSO, ν(CSC) and ν(S=O) appear strongly coupled to the ICT dynamics of curcumin, which supports the strong solvation interactions including the hydrogen bonding. Especially, the ν(CSC) and ν(S=O) modes of DMSO represent the ultrafast (20-50 fs) dynamics with the hydrogen-bonded species upon the ICT of curcumin. However, further explorations on the detailed spectral changes between the “free” and “hydrogen-bonded” species in the ν(CSC) and ν(S=O) mode of DMSO are required to explain the solvation changes of DMSO in the solvation shells with the ultrafast ICT dynamics of chromophores.
Lastly, up-to-date investigations and future directions for the solvation dynamics study with the ultrafast excited-state processes of chromophores are summarized. All the FSRS measurements described in the thesis are based on the stimulated Raman “gain” measurements, where the Raman pump centered at higher frequency and the Raman probe with the lower frequencies complete the stimulated Raman process. Similarly, the stimulated Raman “loss” measurements requires the Raman pump at lower and the Raman probe at higher frequencies. It has been known that the modulations of the Raman probe by the Stokes and anti-Stokes Raman processes in the stimulated Raman “loss” measurements are observed in the opposite contribution while the Stokes and anti-Stokes Raman signals are inseparable in the stimulated Raman “gain” measurements. We propose the possible separation of the long-lasting thermal signals in the solvent vibrational modes of DMSO (observed in the excited-state dynamics of alizarin and curcumin) by combining the stimulated Raman “gain” and “loss” measurements. The “hot” ground-state transitions of the ν(S=O) and ν(CSC) modes of DMSO by the anti-Stokes Raman process can be subtracted with some experimental control between the stimulated Raman “gain” and “loss” measurements. Similarly, the nonlinear cross-phase modulation artifacts can be minimized by the control experiment only with the solvent. Further experimental developments are required, however, for more accurate determination of the solvation dynamics of DMSO, which may indirectly “probe” the ultrafast chemical reaction dynamics of chromophores in the excited state including the proton and charge transfer.
In this thesis research, the ultrafast chemical reactions of intramolecular proton and charge transfers have been observed by time-resolved electronic and vibrational spectroscopy. FSRS presents numerous advantages in the reaction dynamics study in the excited state due to its high temporal and spectral resolutions and multimodal vibrational probes in a wide spectral range. The ultrafast chemical reaction dynamics in the excited state can also be probed by the instantaneous changes in the solvent vibrational modes of DMSO including the hydrogen bonding interactions when the strong solvation dynamics exists between the chromophore and solvent molecules.Docto
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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