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Characterization of ca2 through resonant excitation and dispersed laser-induced fluorescence (lif) spectroscopy
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Previous issue date: 26Alkali earth metal dimers, specifically Ca, are of theoretical interest [1,2] due to their weakly bound X ground state, arising from a fully occupied anti-bonding molecular orbital. Experimentally, alkali earth metals are of interest for ultra-cold chemical and physics applications. Due to their similar electronic structure to that of alkali metal atoms, alkali earth metal ions can be laser-cooled and readily formed in Coulomb crystals[3,4]. By inducing reactions, molecular ions can be generated within the Coulomb crystal, where they are translationally cooled by the surrounding atomic ions. Photodissociation techniques can then be used to detect the molecular ions via depletion. In the case of Ca, there are few available spectroscopic data that can be used to determine the frequencies of vibronic transitions that could be intermediates for photodissociation spectroscopy. To obtain such information, the neutral Ca dimer should be spectroscopically characterized in greater detail. Previous spectroscopic efforts have observed vibronic emissions from the strongly perturbed A and B states to the ground state[1]. In this work, Ca was created through laser ablation and supersonic expansion techniques, jet-cooled to 4K. Using an excimer-pumped dye laser, resonant and dispersed laser-induced fluorescence (LIF, DLIF) were performed. Dispersed LIF was detected by sending the fluorescence through a monochromator and detecting dispersed fluorescence with a photomultiplier tube (PMT). Lifetimes of emitting states were also measured. For the first time, the c-X vibronic transitions of Ca were experimentally observed. Using DLIF, vibrational sequences in the X state were observed, confirming X as the emission’s lower state.
[1] Bondybey, V. et al. Chem. Phys. Lett. 1984, 111, 195
[2] Allard, O. et al. Eur. Phys. J. D 2005, 35, 483
[3] Nguyen, J. et al. New. J. Phys. 2011, 13, 063023
[4] Calvin, A. et al. J. Phys. Chem. Lett. 2018, 9, 579
Energy pooling, ion recombination, and reactions of rubidium and cesium in hydrocarbon gasses
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Previous issue date: 6Diode Pumped Alkali Lasers (DPAL) are continuous wave lasers, potentially capable of megawatt average powers. These lasers exploit the D1 and D2 lines of alkali metals resulting in a 3-level laser with the lasing transition in the near infrared region of the electromagnetic spectrum. Energy pooling processes involving collisions between excited alkali metals cause a fraction of the gain media to be highly excited and eventually ionized. These high energy cesium atoms and ions chemically react with small hydrocarbons utilized as buffer gasses for the system, depleting the gain media. A kinetic model supported by experimental data is introduced to explain the cumulative effects of optical trapping, energy pooling, and chemical reactivity in heavy alkali metal (Rb, Cs) systems. Spectroscopic studies demonstrating metal hydride formation will also be presented
Two-dimensional laser induced fluorescence spectroscopy of MgOMg
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Previous issue date: 2019-06-19Two-dimensional laser induced fluorescence spectroscopy is typically implemented using a monochromator equipped with an array detector to record segments of the dispersed fluorescence spectra for each laser excitation wavelength. When pulsed laser excitation is used the capabilities of this system for disentangling complex spectra can be further enhanced by time-gating the array detector. In the present work we are using an Intensified Charge-coupled Device (iCCD) that provides nanosecond time resolution and detection sensitivities that are comparable to photomultiplier tubes. We describe the marriage of a refurbished monochromator, an iCCD, and an Arduino microcontroller to collect temporally and spatially resolved emission spectra of transient small molecules. Recent data for the electronic transitions of the hypermetallic oxide MgOMg will be presented
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
Perturbations of the a’1π and c1σ+ states of cao
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Previous issue date: 25The electronic structure of CaO is complex due to the large number of low-lying energy states and a multitude of rovibronic interactions among them. Several vibrionic bands of the CaO have been identified in the visible region using laser induced fluorescence. Analysis of these rotationally resolved data provides more accurate band origins and rotational constants for levels that were previously determined indirectly using perturbation data. Fluorescence decay lifetime measurements were used to determine the radiative decay rate for the state.
A previously noted homogeneous perturbation of the state was examined to determine the identity of the perturbing state. Dispersed fluorescence spectra and fluorescence decay rate measurements were used to show that the perturbation results from the interaction with a state of symmetry
Cesium ionization and recombination
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Previous issue date: 6Diode Pumped Alkali Lasers (DPALS) are promising candidates for high-power directed energy applications including data transmission and ballistics defense. Selection of an appropriate buffer gas for the gain media requires absence of undesirable chemical reactions while still meeting the kinetic requirements of the system. Small hydrocarbons have been investigated as a potential buffer gas, and while these meet many of the kinetic requirements of the system, they produce unwanted side products, depleting the gain media. Recent measurements including Laser Induced Fluorescence (LIF), dispersed fluorescence, and ion lifetime measurements indicate that the dominant pathway to the products involves ions and highly excited alkali atoms with very long relaxation times
Perturbations Of The A’<sup>1</sup>Π And C<sup>1</sup>Σ<sup>+</sup> States Of Cao
No full textThe electronic structure of CaO is complex due to the large number of low-lying energy states and a multitude of rovibronic interactions among them. Several vibrionic bands of the CaO have been identified in the visible region using laser induced fluorescence. Analysis of these rotationally resolved data provides more accurate band origins and rotational constants for levels that were previously determined indirectly using perturbation data. Fluorescence decay lifetime measurements were used to determine the radiative decay rate for the state.
A previously noted homogeneous perturbation of the state was examined to determine the identity of the perturbing state. Dispersed fluorescence spectra and fluorescence decay rate measurements were used to show that the perturbation results from the interaction with a state of symmetry.Made available in DSpace on 2021-09-24T21:09:36Z (GMT). No. of bitstreams: 2
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