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  • 1
    Electronic Resource
    Electronic Resource
    Reaction cross section and product ion time-of-flight measurements for collisions of N+ and N+2 with CO2 at suprathermal energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7780-7786 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charge exchange and dissociative ionization cross sections are reported for N+–CO2 and N+2–CO2 collisions at center-of-mass energies between 2 and 40 eV. Product ion kinetic energies are measured using time-of-flight techniques. Energy resonance considerations based on CO2 ionization Franck–Condon factors predict charge exchange to be slow for both of these reaction pairs. The N+–CO2 charge exchange, however, exhibits a large cross section and proceeds about one order of magnitude faster than the N+2–CO2 charge exchange. The formation of CO+ in N+–CO2 collisions is reported, while no dissociative ionization products are observed in the N+2–CO2 system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459358
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  • 2
    Electronic Resource
    Electronic Resource
    Cross section and product time-of-flight measurements of the reaction of N+2 with H2O and D2O at suprathermal energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1117-1125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charge exchange and hydrogen atom pickup cross sections, and product ion time-of-flight measurements are reported for N+2 –H2O(D2O) collisions at center-of-mass collision energies ranging between 1 and 15 eV. No isotope effect is detected for the charge exchange branch, while a significant isotope effect is observed for the atom pickup reaction. Throughout the measured energy range, the time-of-flight measurements show that the H2O+(D2O+) charge exchange product is produced with near-thermal energy in the laboratory frame, implying little or no momentum transfer. The charge exchange reaction products are therefore formed with internal energy comparable to the exothermicity of the reaction (2.96 eV). The atom pickup ion product velocity distributions and the atom pickup isotope effect are consistent with a spectator stripping mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458173
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  • 3
    Electronic Resource
    Electronic Resource
    Cross sections and product kinetic energy analysis of H2O+–H2O collisions at suprathermal energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3196-3206 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of H2O+ with H2O is studied using a longitudinal geometry double mass spectrometer in the collision energy range Ec.m.=0.5–25 eV. Cross sections are reported for oxonium ion (H3O+) production and the symmetric charge exchange. Isotopic substitution is used to discern the product branches, including the separation of the two channels for oxonium ion production: (i) proton transfer to the target molecule; and (ii) atom pickup by the primary ion. The largest branching ratio is observed for the charge exchange channel, where no isotope effect is detected in the investigated energy range. Proton transfer exhibits the second largest branching ratio and accounts for more than 90% of the oxonium ion production throughout the measured energy range. The proton transfer cross section is dependent on isotopic substitution, while the atom pickup channel is too weak to make a distinct statement on its isotopic behavior. Product ion energies, determined by time-of-flight measurements, are also reported for each of the three channels. These measurements show that most (〉95%) of the oxonium ions are formed via a direct, spectator stripping type mechanism while a small amount of reaction products exhibit considerable internal excitation. The charge exchange secondary ions are primarily formed at near-thermal energies in the laboratory frame. Small amounts of high laboratory energy product ions are also observed which at least partly originate through the dissociation of excited oxonium ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458852
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  • 4
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence measurements of drift-velocity distributions for Ba+ in Ar: Moment analysis and a direct measure of skewness (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5118-5127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Velocity distributions for Ba+ ions drifting in argon under the influence of an electric field are measured using single-frequency, laser-induced fluorescence techniques. A moment analysis of these data yields values for the ion mobilities, temperatures, and, for the first time, skewness parameters of the ion velocity distributions. Doppler profiles of the drifting ions are obtained with the laser beam propagating both parallel and perpendicular to the electric field direction as a function of E/N up to 148 Td. The velocity-component distributions perpendicular to the electric field direction are nearly Maxwellian at all E/N values studied, but the parallel distributions become noticeably skewed toward high velocities at the largest electric field strengths. The reduced mobilities for Ba+ in Ar, obtained from the first moments of the parallel velocity-component distributions, increase from 1.80±0.16 cm2 V−1 s−1 at zero field to 2.38±0.11 cm2 V−1 s−1 at 148 Td. The second central moments, which describe the widths of the distributions, increase monotonically with increasing E/N values for both the parallel and perpendicular distributions. Temperatures derived from the second central moments agree well with those calculated from a parametrized version of the three-temperature theory [M. Waldman and E. A. Mason, Chem. Phys. 58, 121 (1981)]. The third central moments of the parallel velocity-component distributions characterize the asymmetry of the distributions. Skewness parameters derived from the third central moments increase with electric field strength over the range of E/N studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458649
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  • 5
    Electronic Resource
    Electronic Resource
    Chemiluminescence measurements of the N+2, N++H2O charge transfer systems at suprathermal energies: Direct probe of the dynamics of large cross section charge transfer processes (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9189-9191 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemiluminescence from suprathermal N+2–H2O and N+–H2O collisions is studied using a new experiment. Intense H2O+A˜ 2A1–X˜ 2B1 emission is observed from the N+2 +H2O charge transfer whereas no emissions are detected from the N+–H2O system. OH A 2Σ+–X 2Π emission originating from the N+2+H2O atom pickup channel is also observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459208
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  • 6
    Electronic Resource
    Electronic Resource
    Laser probing of ion velocity distributions in drift fields: Parallel and perpendicular temperatures and mobility for Ba+ in He (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4707-4715 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of ion velocity distributions are presented for Ba+ drifted in helium under well characterized conditions using single-frequency laser-induced fluorescence probing. We present the reduced mobilities and the Doppler profiles parallel and perpendicular to the electric field vector as a function of the ratio of the field strength (E) to the buffer gas density (N) up to 33.5 Td. The reduced mobility decreases monotonically with increasing E/N from the zero-field value of 16.7±0.4 cm2 V−1 s−1 at 313 K. The parallel and perpendicular ion temperatures are in very good agreement with both a repulsive Maxwell model and a parametrized version of the three-temperature theory of Lin et al. The parallel temperature is always higher than the perpendicular one. Effects of optical pumping on the Doppler profiles are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455665
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  • 7
    Electronic Resource
    Electronic Resource
    Laser probing of the rotational alignment of N+2 drifted in helium (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6029-6039 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results are presented on laser-induced fluorescence studies of the rotational alignment of N+2 drifted in helium. The alignment which is caused by collisions of the ions with the helium buffer gas is observed in the uniform electric field of a drift tube. The angular momentum vectors of the ions are preferentially aligned perpendicular to the electric field vector. At a drift field of 14 Td, corresponding to a collision energy of 52 meV (c.m.), a quadrupole moment A(2)0=−0.11±0.03 is determined for the N=10 rotational state. This yields an approximate population ratio of 2:3 for finding molecules with rotational angular momentum vectors parallel and perpendicular to the electric field vector, respectively. In addition to the alignment studies, a detailed characterization of the drift tube using laser-induced fluorescence detection of N+2 is presented. Theoretical results for the determination of alignment parameters using saturated laser-induced fluorescence are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453475
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  • 8
    Electronic Resource
    Electronic Resource
    Direct observation of Ba+ velocity distributions in a drift tube using single-frequency laser-induced fluorescence (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5578-5579 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First results are presented on velocity distribution measurements of Ba+ ions drifted in helium using a well-characterized drift tube and single-frequency laser-induced fluorescence detection. Reduced mobilities of Ba+ in helium are obtained for E/N values between 7.74 and 23.2 Td. The velocity distributions that are observed parallel to the electric field fit a displaced Maxwell–Boltzmann distribution, in agreement with theoretical predictions. However, the temperatures parallel and perpendicular to the field are not in good agreement with theoretical treatments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453642
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  • 9
    Electronic Resource
    Electronic Resource
    Collision-induced dissociation dynamics in O2++Ne(Ar) collisions: The role of electronic excitation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8561-8566 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Integral collision-induced dissociation (CID) cross sections at center-of-mass (CM) energies ranging from threshold to 22 eV and product ion recoil velocity distributions are presented for O2++Ne(Ar) collisions. The O2+ ions are produced in an electron impact ion source and thus have ∼0.5 eV of vibrational energy. The O2++Ne CID cross sections are observed at energies below the 0 K thermodynamic threshold of 6.66 eV, implying the possibility of significant vibrational effects. A second CID threshold is apparent at 9±1 eV. This is close to the charge-transfer (CT) threshold energy. No CT products are observed. The O2++Ar CID cross section rises rapidly above a relative translational energy onset of 7.5±0.2 eV and reaches a maximum value of ∼0.8 Å2 at 14 eV (CM). A CT onset of 6.0±0.2 eV is observed which is close to the thermodynamic threshold for CID. The energy dependence of the CT cross section is very similar to the CID cross section except for a small step at energies where CID becomes efficient. The CID recoil velocity distributions near threshold are centered at the CM velocity and shift to forward preference at higher energies. The O2++Ar CT recoil velocities are forward scattered near threshold and become centered with respect to the CM velocity at energies where competition with CID is apparent. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1317550
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  • 10
    Electronic Resource
    Electronic Resource
    Collision-induced dissociation dynamics of Ar2+ at high levels of vibrational excitation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10880-10889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The collision-induced dissociation (CID) dynamics of the Ar2++Ar collision system are investigated at different Ar2+ internal energy distributions in a guided-ion beam (GIB) apparatus. The internal energy of reactant ions, assumed vibrational in a first approximation, is controlled by varying the position of ionization in a supersonic jet, electron impact ion source. Three conditions are investigated: cold, in which the ions are produced as vibrationally relaxed as possible; intermediate, in which a substantial shift in the CID onset is observed; hot, in which the apparent CID threshold is at near thermal collision energies. The vibrational distribution of the Ar2+ ions is probed at the same conditions by measuring the kinetic energy release of photofragment Ar+ following 2Σg+←2Σu+ photodissociation. The derived internal energy distributions are then used to model the observed CID cross sections with a modified line-of-centers approach to assess vibrational effects in the single-collision cross sections. The intermediate CID cross sections are consistent with a negligible vibrational enhancement beyond the statistical predictions. A substantial increase in cross section is observed when going from intermediate to hot conditions, despite a weak increase in internal energy, as apparent from the photodissociation measurements. Contributions from metastable states, not registered in the photodissociation experiment, can explain this disparity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481728
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