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Data for First Responder Use of Photoionization Detectors for Vapor Chemical Constituents

Description: First responders need appropriate measurement technologies for evaluating incident scenes. This report provides information about photoionization detectors (PIDs), obtained from manufacturers and independent laboratory tests, and the use of PIDs by first responders, obtained from incident commanders in the United States and Canada. PIDs are valued for their relatively low cost, light weight, rapid detection response, and ease of use. However, it is clear that further efforts are needed to provide suitable instruments and decision tools to incident commanders and first responders for assessing potential hazardous chemical releases. Information provided in this report indicates that PIDs should always be part of a decision-making context in which other qualitative and more definitive tests and instruments are used to confirm a finding. Possible amelioratory actions ranging from quick and relatively easy fixes to those requiring significant additional effort are outlined in the report.
Date: November 1, 2006
Creator: Daum, Keith A.; Watrous, Matthew G.; Neptune, M. Dean; Michael, Daniel I.; Hull, Kevin J. & Evans, Joseph D.
Partner: UNT Libraries Government Documents Department

Photoionization of multiply charged ions at the advanced light source

Description: Photoionization of multiply charged ions is studied using the merged-beams technique at the Advanced Light Source. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences.
Date: October 7, 2004
Creator: Schlachter, A.S.; Kilcoyne, A.L.D.; Aguilar, A.; Gharaibeh, M.F.; Emmons, E.D.; Scully, S.W.J. et al.
Partner: UNT Libraries Government Documents Department

Photoionization of Sc2+ ions by synchrotron radiation: Highresolution measurements and absolute cross sections in the photon energyrange 23-68 eV

Description: Cross sections for photoionization of doubly-chargedscandium ions has been measured using a merged-beams technique. Resultsare compared with the time-reversed process ofphotorecombination.
Date: October 7, 2002
Creator: Schippers, Stefan E.; Müller, A.; Ricz, S.; Bannister, M. E.; Dunn, G. H.; Schlachter, A. S. et al.
Partner: UNT Libraries Government Documents Department

Photoionization and fragmentation of polyatomic molecules

Description: From chemical spectroscopy and photochemistry in the vacuum ultraviolet conference; Valmorin, Quebec, Canada (5 Aug 1973). The discussion of photoionization and fragmentation of polyatomic molecules covers experimental procedures, energy deposition, dissociation processes and the determination of thermochemical quantities, and diatomic and small and large polyatomic molecules. (JFP)
Date: January 1, 1973
Creator: Chupka, W.A.
Partner: UNT Libraries Government Documents Department

Kinetics and Thermochemistry of the Reaction Si(CH₃)₃ + HBr ⇋ Si(CH₃)₃H + Br: Determination of the (CH₃)₃Si-H Bond Energy

Description: Article on kinetics and thermochemistry of the reaction Si(CH₃)₃ + HBr ⇋ Si(CH₃)₃H + Br and determination of the (CH₃)₃Si-H bond energy.
Date: September 1994
Creator: Kalinovski, Ilia J.; Gutman, D.; Krasnoperov, Lev N.; Goumri, Abdellatif; Yuan, W. J. & Marshall, Paul
Partner: UNT College of Arts and Sciences

Symmetrized complex amplitudes for He double photoionization from the time-dependent close coupling and exterior complex scaling methods

Description: Symmetrized complex amplitudes for the double photoionization of helium are computed by the time-dependent close-coupling and exterior complex scaling methods, and it is demonstrated that both methods are capable of the direct calculation of these amplitudes. The results are found to be in excellent agreement with each other and in very good agreement with results of other ab initio methods and experiment.
Date: June 1, 2004
Creator: Horner, D.A.; Colgan, J.; Martin, F.; McCurdy, C.W.; Pindzola, M.S. & Rescigno, T.N.
Partner: UNT Libraries Government Documents Department

Development of Soft Ionization for Particulate Organic Detection with the Aerodyne Aerosol Mass Spectrometer

Description: During this DOE SBIR Phase II project, we have successfully developed several soft ionization techniques, i.e., ionization schemes which involve less fragmentation of the ions, for use with the Aerodyne time-of-flight aerosol mass spectrometer (ToF-AMS). Vacuum ultraviolet single photon ionization was demonstrated in the laboratory and deployed in field campaigns. Vacuum ultraviolet single photon ionization allows better identification of organic species in aerosol particles as shown in laboratory experiments on single component particles, and in field measurements on complex multi-component particles. Dissociative electron attachment with lower energy electrons (less than 30 eV) was demonstrated in the measurement of particulate organics in chamber experiments in Switzerland, and is now a routine approach with AMS systems configured for bipolar, negative ion detection. This technique is particularly powerful for detection of acidic and other highly oxygenated secondary organic aerosol (SOA) chemical functionality. Low energy electron ionization (10 to 12 eV) is also a softer ionization approach routinely available to AMS users. Finally, Lithium ion attachment has been shown to be sensitive to more alkyl-like chemical functionality in SOA. Results from Mexico City are particularly exciting in observing changes in SOA molecular composition under different photochemical/meteorological conditions. More recent results detecting biomass burns at the Montana fire lab have demonstrated quantitative and selective detection of levoglucosan. These soft ionization techniques provide the ToF-AMS with better capability for identifying organic species in ambient atmospheric aerosol particles. This, in turn, will allow more detailed study of the sources, transformations and fate of organic-containing aerosol.
Date: June 19, 2008
Creator: Trimborn, A; Williams, L R; Jayne, J T & Worsnop, D R
Partner: UNT Libraries Government Documents Department

Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol-Water Clusters

Description: In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH+(n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH n(H2O)H+ (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH+, (CH3OH)2+, (CH3OH)nH+ (n = 1-9), and (CH3OH)n(H2O)H+ (n = 2-9) as a function of photon energy. With an increasein the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.
Date: April 24, 2008
Creator: Kostko, Oleg; Belau, Leonid; Wilson, Kevin R. & Ahmed, Musahid
Partner: UNT Libraries Government Documents Department

Experimental observation of guanine tautomers with VUV photoionization

Description: Two methods of preparing guanine in the gas phase, thermal vaporization and laser desorption, have been investigated. The guanine generated by each method is entrained in a molecular beam, single photon ionized with tunable VUV synchrotron radiation, and analyzed using reflectron mass spectrometry. The recorded photoionization efficiency (PIE) curves show a dramatic difference for experiments performed via thermal vaporization compared to laser desorption. The calculated vertical and adiabatic ionization energies for the eight lowest lying tautomers of guanine suggest the experimental observations arise from different tautomers being populated in the two different experimental methods.
Date: December 1, 2008
Creator: Zhou, Jia; Kostko, Oleg; Nicolas, Christophe; Tang, Xiaonan; Belau, Leonid; de Vries, Mattanjah S. et al.
Partner: UNT Libraries Government Documents Department

A velocity map imaging spectrometer for electron?ion and ion?ion coincidence experiments with synchrotron radiation

Description: We have built a velocity imaging (VMI) spectrometer optimized for angle-resolved photoionization experiments with synchrotron radiation (SR) in the VUV and soft X-tay range. The spectrometer is equiped with four electrostatic lenses that focus the charged photoionization products onto a position-sensitive multi-hit delay-line anode. The use of two additional electrostatic lens elements as compared to the standard design of Eppink and Parker [T.J.B. Eppink and D.H. Parker, Rev. Sci. Instrum. 68 (1997) 3477]provides better focusing of an extended interaction region, which is crucial for most SR applications. Furthermore, the apparatus is equipped with a second micro-channel plate detector opposite to the VMI spectrometer, enabling electron-ion coincidence experiments and thereby mass-resolved ion spectroscopy independent of the time structure of the synchrotron radiation. First results for the photofragmentation of CO2 molecules are presented.
Date: April 27, 2007
Creator: Lawrence Berkeley National Laboratory. Advanced Light Source.
Partner: UNT Libraries Government Documents Department

The Multiplexed Chemical Kinetic Photoionization Mass Spectrometer: A New Approach To Isomer-resolved Chemical Kinetics

Description: We have developed a multiplexed time- and photon-energy?resolved photoionizationmass spectrometer for the study of the kinetics and isomeric product branching of gasphase, neutral chemical reactions. The instrument utilizes a side-sampled flow tubereactor, continuously tunable synchrotron radiation for photoionization, a multi-massdouble-focusing mass spectrometer with 100percent duty cycle, and a time- and positionsensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed 3-dimensional data structure (intensity as a function of molecular mass, reaction time, and photoionization energy) provides insights that might not be available in serial acquisition, as well as additional constraints on data interpretation.
Date: August 28, 2008
Creator: Osborne, David L.; Zou, Peng; Johnsen, Howard; Hayden, Carl C.; Taatjes, Craig A.; Knyazev, Vadim D. et al.
Partner: UNT Libraries Government Documents Department

Theoretical study of asymmetric molecular-frame photoelectron angular distributions for C 1s photoejection from CO2

Description: We report the results of ab initio calculations of cross sections and molecular-frame photoelectron angular distributions for C 1s ionization of CO2, and propose a mechanism for the recently observed asymmetry of those angular distributions with respect to the CO^+and O^+ions produced by subsequent Auger decay. The fixed-nuclei, photoionization amplitudes were constructed using variationally obtained electron-molecular ion scattering wave functions. We have also carried out electronic structure calculations which identify a dissociative state of the CO2^++ dication that is likely populated following Auger decay and which leads to O^+ + CO^+ fragment ions. We show that a proper accounting of vibrational motion in the computation of the photoelectron angular distributions, along with reasonable assumptions about the nuclear dissociation dynamics, gives results in good agreement with recent experimental observations. We also demonstrate that destructive interference between different partial waves accounts for sudden changes with photon energy in the observed angular distributions.
Date: February 18, 2009
Creator: Rescigno, Thomas N; Miyabe, S.; McCurdy, C.W. & Orel, A.E.
Partner: UNT Libraries Government Documents Department

Classical two-slit interference effects in double photoionization of molecular hydrogen at high energies

Description: Recent experiments on double photoionization of H$_2$ with photon energies between 160 and 240 eV have revealed body-frame angular distributions that suggest classical two-slit interference effects may be present when one electron carries most of the available energy and the second electron is not observed. We report precise quantum mechanical calculations that reproduce the experimental findings. They reveal that the interpretation in terms of classical diffraction is only appropriate atsubstantially higher photon energies. At the energies considered in the experiment we offer an alternative explanation based on the mixing of two non-diffractive contributions by circularly polarized light.
Date: July 6, 2008
Creator: Horner, Daniel A.; Miyabe, Shungo; Rescigno, Thomas N; McCurdy, C. William; Morales, Felipe & Martin, Fernando
Partner: UNT Libraries Government Documents Department

Fragmentation pathwaysfor selected electronic states of theacetylene dication

Description: Coincident measurement of the Auger electron and fragmention momenta emitted after carbon core-level photoionization of acetylenehas yielded new understanding of how the dication fragments. Ab initiocalculations and experimental data, including body-frame Auger angulardistributions, are used to identify the parent electronic states andtogether yield a comprehensive map of the dissociation pathways whichinclude surface crossings and barriers to direct dissociation. The Augerangular distributions show evidence of core-holelocalization.
Date: December 18, 2007
Creator: Osipov, Timur; Rescigno, Thomas N.; Weber, Thorsten; Miyabe,Shungo; Jahnke, T.; Alnaser, A. et al.
Partner: UNT Libraries Government Documents Department

Photoionized Features in the X-ray Spectrum of EX Hydrae

Description: We present the first results from a long (496 ks) Chandra High Energy Transmission Grating observation of the intermediate polar EX Hydrae. In addition to the narrow emission lines from the cooling post-shock gas, for the first time we have detected a broad component in some of the X-ray emission lines, namely O VIII {lambda}18.97, Mg XII {lambda}8.42, Si XIV {lambda}6.18, and Fe XVII {lambda}16.78. The broad and narrow components have widths of {approx} 1600 km s{sup -1} and {approx} 150 km s{sup -1}, respectively. We also find that the flux of the broad component is modulated at the white dwarf spin period, constraining the region where the gas is formed. We propose a scenario where the broad component is formed in the pre-shock flow photoionized by radiation from the post-shock flow. Because the photoionized region has to be close to the radiation source in order to produce strong photoionized emission lines from ions like O VIII, Mg XII, and Si XIV, our photoionization model constrains the height of the standing shock above the white dwarf surface.
Date: September 28, 2009
Creator: Luna, G M; Raymond, J C; Brickhouse, N S; Mauche, C W; Proga, D; Steeghs, D et al.
Partner: UNT Libraries Government Documents Department

High resolution photoelectron images and D{sup +} photofragment images following 532-nm photolysis of D{sub 2}

Description: The non-resonant ionization and dissociation of D{sub 2} by intense 532-nm laser light is studied by a variation of the ``Ion Imaging`` technique called ``Velocity Mapping``. Images of the both the photoelectrons and D{sup +} photofragments are obtained and analyzed at two different laser intensities. Results are compared to previous studies and several differences are discussed.
Date: January 1, 1998
Creator: Chandler, D.W.; Neyer, D.W. & Heck, A.J.
Partner: UNT Libraries Government Documents Department

A preliminary report on the photoionization efficiency spectrum, ionization energy and heat of formation of Br{sub 2}O; and the appearance energy of BrO{sup +} (Br{sub 2}O)

Description: We report experimental results for the photoionization efficiency (PIE) spectrum of Br{sub 2}O along with the ionization energy (derived form the ionization threshold) and the appearance energy (AE) of BrO{sup +} (Br{sub 2}O). A value for the heat of formation of Br{sub 2}O is derived form the AE result. Experiments were performed by employing a discharge flow-photoionization mass spectrometer (DF-PIMS) apparatus coupled to beamline U-11 at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory.
Date: August 1, 1995
Creator: Thorn, R. P., Jr.; Monks, P. S.; Stief, L. J.; Kuo, S. C.; Zhang, Z. & Klemm, R. B.
Partner: UNT Libraries Government Documents Department

Femtosecond laser postionization of sputtered and laser desorbed atoms

Description: This paper examines the photoionization efficiency of a femtosecond laser ionization source on several atomic species. Use of femtosecond laser ionization pulses to photoionize the desorbing flux from a sample surface is examined. Example of mass spectra produced is given using 248 nm pulse on sputtered Au. Al and Mo have widely different ionization potentials and show that 248 nm pulses are more efficient at photoionization than longer wavelengths; this is enhanced for Mo with high ionization potential. It is concluded that efficient photoionization occurs for atoms with ionization potentials low enough for two-photon ionization to occur.
Date: June 1, 1995
Creator: Pellin, M.J.; Lykke, K.R. & Calaway, W.F.
Partner: UNT Libraries Government Documents Department

Dynamics of ultrafast internal conversion processes studied by femtosecond time-delayed photoelectron spectroscopy

Description: The authors have studied the dynamics of ultrafast internal conversion processes using femtosecond time-resolved photoionization and photoelectron spectroscopy. In hexatriene, following femtosecond pulse excitation at 250 nm, they use time-delayed photoionization to observe the formation and decay of an intermediate species on the subpicosecond time scale. With time-resolved photoelectron spectroscopy, the rapid evolution of vibrational excitation in this intermediate is observed, as electronic energy is converted to vibrational energy in the molecule. The photodynamics of cis and trans isomers of hexatriene are compared and found to be surprisingly different on the 2-3 psec time scale. These results are important for understanding the fundamental photochemical processes in linear polyenes, which have served as models for the active chromophores of many biological photosystems.
Date: August 1, 1995
Creator: Cyr, D.R. & Hayden, C.C.
Partner: UNT Libraries Government Documents Department

Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au

Description: A new mass spectrometry surface imaging method is presented in which ion-sputtered neutrals are postionized by wavelength-tunable vacuum ultraviolet (VUV) light from a synchrotron source. Mass spectra and signal counts of the photoionized neutrals from GaAs (100) and Au are compared to those of the secondary ions. While clusters larger than dimers are more efficiently detected as secondary ions, certain species, such as As2, Au and Au2, are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered Asm (m=1,2) and Aun (n=1-4). From the observed ionization thresholds, sputtered neutral As and Au show no clear evidence of electronic excitation, while neutral clusters have photoionization onsets shifted to lower energies by ~;;0.3 eV. These shifts are attributed to unresolved vibrational and rotational excitations. High-spatial resolution chemical imaging with synchrotron VUV postionization is demonstrated at two different photon energies using a copper TEM grid embedded in indium. The resulting images are used to illustrate the use of tunable VUV light for verifying mass peak assignments by exploiting the unique wavelength-dependent PIE of each sputtered neutral species. This capability is valuable for identifying compounds when imaging chemically complex systems with mass spectrometry-based techniques.
Date: December 5, 2008
Creator: Takahashi, Lynelle; Zhou, Jia; Wilson, Kevin R.; Leone, Stephen R. & Ahmed, Musahid
Partner: UNT Libraries Government Documents Department

A VUV photoionization measurement and ab-initio calculation of the ionization energy of gas phase SiO2

Description: In this work we report on the detection and vacuum-ultraviolet (VUV) photoionization of gas phase SiO2 generated in situ via laser ablation of silicon in a CO2 molecular beam. The resulting species are investigated by single photon ionization with tunable VUV synchrotron radiation and mass analyzed using reflectron mass spectrometry. Photoionization efficiency (PIE) curves are recorded for SiO and SiO2 and ionization energy estimates are revealed from such measurements. A state-to-state ionizationenergy of 12.60 (+-0.05) eV is recorded by fitting two prominent peaks in the PIE curve for the following process: 1SUM O-Si-O --> 2PRODg [O-Si-O]+. Electronic structure calculations aid in the interpretation of the photoionization process and allow for identification of the symmetric stretch of 2PRODg [O-Si-O]+ which is observed in the PIE spectrum to be 0.11 eV (890 cm-1) above the ground state of the cation and agrees with the 892 cm-1 symmetric stretch frequency calculated at the CCSD(T)/aug-cc-pVTZ level.
Date: December 5, 2008
Creator: Kostko, Oleg; Ahmed, Musahid & Metz, Ricardo B.
Partner: UNT Libraries Government Documents Department