Soft x-ray ionization induced fragmentation of glycine

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Gas-phase study on uridine: Conformation and X-ray photofragmentation

Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses ≤43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal formFinancial support from the Academy of Finland, the European COST Action XLIC CM1204 and the EU Transnational Access to Research Infrastructures programme. Computational resources from the FGI project (Finland) are acknowledged. D.T.H. acknowledges the Finnish Cultural Foundation for funding and the MINECO Project No. FIS2013-42002- R. E.R. acknowledges funding from the Swedish Research Council (VR

Fragmentation patterns of 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole - The effect of the methylation

We present here the photofragmentation patterns of doubly ionized 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole. The doubly ionized state was created by core ionizing the C 1s orbitals of the samples, rapidly followed by Auger decay. Due to the recent development of nitroimidazole-based radiosensitizing drugs, core ionization was selected as it represents the very same processes taking place under the irradiation with medical X-rays. In addition to the fragmentation patterns of the sample, we study the effects of methylation on the fragmentation patterns of nitroimidazoles. We found that methylation alters the fragmentation significantly, especially the charge distribution between the final fragments. The most characteristic feature of the methylation is that it effectively quenches the production of NO and NO+, widely regarded as key radicals in the chemistry of radiosensitization by the nitroimidazoles

Size selective spectroscopy of Se microclusters

The electronic structure and photofragmentation in outer and inner valence regions of Se-n (n <= 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectron-photoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se-n microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se-n clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737633

Photoelectron recoil in CO in the x-ray region up to 7 keV

Carbon 1s photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from ν=0 to 3 within the vibrational progression of the C 1s photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results

Chemiresistor microsensors for in-situ monitoring of volatile organic compounds : final LDRD report.

This report provides a summary of the three-year LDRD (Laboratory Directed Research and Development) project aimed at developing microchemical sensors for continuous, in-situ monitoring of volatile organic compounds. A chemiresistor sensor array was integrated with a unique, waterproof housing that allows the sensors to be operated in a variety of media including air, soil, and water. Numerous tests were performed to evaluate and improve the sensitivity, stability, and discriminatory capabilities of the chemiresistors. Field tests were conducted in California, Nevada, and New Mexico to further test and develop the sensors in actual environments within integrated monitoring systems. The field tests addressed issues regarding data acquisition, telemetry, power requirements, data processing, and other engineering requirements. Significant advances were made in the areas of polymer optimization, packaging, data analysis, discrimination, design, and information dissemination (e.g., real-time web posting of data; see www.sandia.gov/sensor). This project has stimulated significant interest among commercial and academic institutions. A CRADA (Cooperative Research and Development Agreement) was initiated in FY03 to investigate manufacturing methods, and a Work for Others contract was established between Sandia and Edwards Air Force Base for FY02-FY04. Funding was also obtained from DOE as part of their Advanced Monitoring Systems Initiative program from FY01 to FY03, and a DOE EMSP contract was awarded jointly to Sandia and INEEL for FY04-FY06. Contracts were also established for collaborative research with Brigham Young University to further evaluate, understand, and improve the performance of the chemiresistor sensors