1,721,671 research outputs found
Ultrafast isomerization initiated by X-ray core ionization
No full textRapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a ‘molecular movie’ of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.United States. Dept. of Energy. Office of Basic Energy Science
A Trans-Pacific Collaboration: Dynamical Experiments and Experiences
No full textI first met Soji Tsuchiya in 1979 at the XIV International Symposium on Free Radicals at the Kwansai Gakuin University in Sanda. At that time I had no idea what an enormous impact we would have on each other. In fact, Soji is almost completely absent from my memories of the meeting. My memories of that trip are dominated by my overwhelming first impressions of Japan, my first meeting with Soji’s collaborator, Katsumi Sakurai (to whom I owned my initial scientific success as a postdoc with the late H.P. Broida, but that is another story), and one incredible post-conference day in Tokyo in which David Harris and I visited both the Hongo and Komaba campuses of the University of Tokyo and the Tokyo Institute of Technology (and gave talks at two of the three universities)! I remember discussing the Tsuchiya-Sakurai plan for "cascade type excitation" with Katsumi and realizing how lucky it was for me that our essentially identical "Stimulated Emission Pumping" experiments on 12 had already begun to work. But at that time I had absolutely no interest in polyatomic molecules, especially none in IVR or chaos, and I suspect Soji and Katsumi had little or no interest in diatomic molecules. If it were not for my collaborator at MIT, Jim Kinsey, Soji Tsuchiya and I would probably not have collided so strongly and fruitfully
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Perspective: The first ten years of broadband chirped pulse Fourier transform microwave spectroscopy
No full textSince its invention in 2006, the broadband chirped pulse Fourier transform spectrometer has transformed the field of microwave spectroscopy. The technique enables the collection of a ≥10 GHz bandwidth spectrum in a single shot of the spectrometer, which allows broadband, high-resolution microwave spectra to be acquired several orders of magnitude faster than what was previously possible. We discuss the advantages and challenges associated with the technique and look back on the first ten years of chirped pulse Fourier transform spectroscopy. In addition to enabling faster-than-ever structure determination of increasingly complex species, the technique has given rise to an assortment of entirely new classes of experiments, ranging from chiral sensing by three-wave mixing to microwave detection of multichannel reaction kinetics. However, this is only the beginning. Future generations of microwave experiments will make increasingly creative use of frequency-agile pulse sequences for the coherent manipulation and interrogation of molecular dynamics.United States. Dept. of Energy. Office of Basic Energy Sciences. Chemical Sciences, Geosciences, & Biosciences Division (Grant DE-FG0287ER13671)National Science Foundation (U.S.) (Grant CHE-1361865)Petroleum Research Fund (Grant 50650-ND6
Comparison of anionic membranes used to concentrate nitric acid to beyond the azeotropic mixture
No full textThe electrolysis of concentrated nitric acid solutions was carried out in an electrochemical cell with parallel plates (FM01-LC ICI). An anionic membrane that permits the migration of nitrate ions under the influence of an electrical field separated the anodic and cathodic compartments. The current efficiency for the transported nitrate ions was evaluated for several membranes, at a constant current. All the membranes allowed the transport of nitrate ions at different current efficiencies, following the increase in acid concentration in the anodic compartment. This electroseparation membrane process concentrated nitric acid from 25% up to 90% in successive stages. A special case to be noted was when the acid concentration was near the azeotropic value. In this case, the acid concentration in the anodic compartment rose above the azeotropic value of 68.5%, thus breaking the azeotrope mixture. It is expected that, for some niche applications, this process could be competitive with extractive distillation
Edge effects in chirped-pulse Fourier transform microwave spectra
No full textRecent applications of chirped-pulse Fourier transform microwave and millimeter wave spectroscopy have motivated the use of short (10–50 ns) chirped excitation pulses. In this regime, individual transitions within the chirped pulse bandwidth do not all, in effect, experience the same frequency sweep through resonance from far above to far below (or vice versa), and “edge effects” may dominate the relative intensities. We analyze this effect and provide simplifying expressions for the linear fast passage polarization response in the limit of long and short excitation pulses. In the long pulse limit, the polarization response converges to a rectangular function of frequency, and in the short pulse limit, the polarization response morphs into a form proportional to the window function of the Fourier-transform-limited excitation pulse.United States. Dept. of Energy. Office of Basic Energy Sciences (DE-FG0287ER13671
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