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  • 1
    Electronic Resource
    Electronic Resource
    Electron impact ionization of the hydroxyl radical (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 932-936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We employed the fast-neutral-beam technique in a measurement of absolute partial cross sections for the electron-impact ionization and dissociative ionization of the hydroxyl free radical from threshold to 200 eV. The deuterated OD radical rather than the protonated OH radical was used as a target in our studies in order to allow a better separation of the various product ions in our apparatus. The total (single) OD ionization cross section was found to have a value of slightly less than 2.0×10−16 cm2 at 70 eV. The ionization of OD is dominated by the formation of parent ions with a parent ionization cross section of 1.85×10−16 cm2 at this energy. A comparison of the experimentally determined total single OD ionization cross section with a calculated OH cross section using a modified additivity rule showed good agreement in terms of the absolute value and the cross section shape (at least above 50 eV). In the course of this work, we also measured the partial ionization cross sections for the D2O molecule and found good agreement between our cross sections and the most recent measurements of Straub et al. [J. Chem. Phys. 108, 109 (1998)] as well as with recent calculations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476635
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  • 2
    Electronic Resource
    Electronic Resource
    Electron impact ionization of the SF5 and SF3 free radicals (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6596-6600 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured absolute cross sections for the electron-impact ionization and dissociative ionization of the SF5 and SF3 free radicals from threshold to 200 eV using the fast-neutral-beam technique. The total single ionization cross sections at 70 eV were found to be 5.1×10−16 cm2 (SF5) and 3.2×10−16 cm2 (SF3). The cross sections reach their maximum at about 100 eV for both radicals, with values of 5.4×10−16 cm2 (SF5) and 3.5×10−16 cm2 (SF3). Dissociative ionization is important only for SF5, where the SF5+ parent ionization cross section and the SF4+ fragment ionization cross sections have roughly the same value. By contrast, the ionization of SF3 is dominated by the formation of SF3+ parent ions. A comparison of the measured total single ionization cross sections with calculated cross sections, using a modified additivity rule, shows excellent agreement for both radicals in terms of the absolute cross section values and the cross section shapes. Total single ionization cross sections were also calculated for SF4, SF2, and SF. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477311
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  • 3
    Electronic Resource
    Electronic Resource
    Absolute cross sections for the electron impact ionization of the NF2 and NF free radicals (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5626-5630 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of the absolute cross sections for the electron-impact ionization of the NF2 and NF free radicals from threshold to 200 eV. At 70 eV, the absolute parent NF2 and NF ionization cross section are 1.25±0.23 A(ring)2 and 1.05±0.19 A(ring)2, respectively. We found little evidence of the presence of vibrationally excited radicals in the incident target beam for both NF2 and NF. We also studied the dissociative ionization of NF2 and NF. The absolute cross section for the formation of the NF+ fragment ions from NF2 was found to be 0.75±0.15 A(ring)2 at 70 eV. The NF+ fragment ions are formed with little excess kinetic energy. The only significant pathway leading to the observed NF+ fragment ions is the single positive ion formation. Our data show no indication of the presence of double positive ion formation channels or positive–negative ion pair formation processes. Cross sections for the formation of the atomic fragment ions F+ and N+ from both NF2 as well as NF were found to be small with maximum values of less than 0.1 A(ring)2 at 70 eV in all cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467129
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  • 4
    Electronic Resource
    Electronic Resource
    Electron impact ionization of the SO2 molecule (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 211-218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of the absolute cross sections for the electron-impact ionization of SO2 from threshold to 200 eV. Absolute cross sections for the formation of the SO+2 parent ions and of the SO+, S+, O+, and O+2 fragment ions were obtained independently in two different laboratories using two different experimental techniques with uncertainties ranging from ±18% to ±25%. The level of agreement between the absolute cross sections (at 70 eV) obtained by the two techniques ranges from about 10% for SO+2 and SO+ to 20% for (S++O+2) and O+, which in all cases is well within the combined error margins of the two measurements. The high resolution capability of the mass spectrometer employed in one experiment enabled the separation of the S+ and O+2 fragment ions, which are separated by only 0.017 76 atomic mass units (amu), for the first time. The single positive ion formation is the dominant process for all observed product ions. The total single SO2 ionization cross section obtained by the two techniques agreed to within 8%. A comparison of the experimentally determined total SO2 single ionization cross sections with calculated cross sections based on a modified additivity rule revealed agreement to within 20%. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469634
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  • 5
    Electronic Resource
    Electronic Resource
    Optical emissions from electron-impact-excited tetra-ethoxysilane (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7203-7206 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical emission spectrum in the spectral region 200–800 nm produced by electron impact on tetra-ethoxysilane (TEOS) under controlled single-collision conditions is analyzed. Absolute emission cross sections (at an impact energy of 100 eV) of 0.7±0.2×10−20 cm2 for the Si (3p4s 1P0→3p2 1S) line at 390.6 nm, 2.4±0.5×10−20 cm2 for the CH(A 2Δ→X 2Π) band centered around 430 nm, and cross sections below 0.5×10−20 cm2 for the hydrogen Balmer-α, -β, and -γ lines at, respectively, 656.4, 486.1, and 434.0 nm are measured. Comparatively high onset energies of 56.2±2.0 eV (Si) and 30.7±2.0 eV (CH) were found which when combined with the small cross sections indicate that the single-step dissociative excitation of TEOS by electron impact cannot be expected to play a major role in the collision processes that dominate the plasma chemistry of TEOS-containing processing plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352393
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  • 6
    Electronic Resource
    Electronic Resource
    Measurements of the dc electric dipole polarizabilities of the alkali dimer molecules, homonuclear and heteronuclear (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3894-3904 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The average static (dc) electric dipole polarizabilities of the NaK and KCs heteronuclear alkali dimers have been measured, and those of the homonuclear molecules remeasured using molecular beam deflection in an inhomogeneous electric field. A congruent magnetic field enabled removal of the monomer constituents of the beam. The resulting deflection curves reflect both the permanent electric dipole force (for the heteronuclear dimers only), and the induced (polarizability) dipole force. It is assumed that the molecular constituents of the beam possess modified Maxwell–Boltzmann velocity and rotational state distributions. A Mach number is introduced to describe the sonic beam properties. The data analysis consists of a two-parameter least squares best fit of the experimental deflection curves to computed ones, the parameters being the polarizability and the Mach number. Values of the permanent heteronuclear dipole moments are taken from the literature. The obtained static electric dipole polarizabilities in units of (A(ring)3) are 34±3 for Li2 (948 K), 40±3 for Na2 (676 K), 77±6 for K2 (542 K), 79±6 for Rb2 (527 K), 104±8 for Cs2 (480 K), 51±3 for NaK (612 K), and 89±5 for KCs (488 K). Comparison with recent calculations as well as earlier measurements of the homonuclear species are given. Two empirical rules are proposed for determining polarizabilities and dipole moments of heteronuclear molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464017
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  • 7
    Electronic Resource
    Electronic Resource
    Production of fluorine 2,4P→2P0 resonance radiation by electron impact on SF6, CF4, NF3, and CCl2F2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 341-350 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We studied the emission of the fluorine (2p43s) 2,4P→(2p5) 2P resonance lines in the vacuum ultraviolet (VUV) at 95.5 and 97.5 nm, respectively, following dissociative excitation of SF6, CF4, NF3, and CCl2F2 by controlled electron impact under single collision conditions. Absolute photoemission cross sections and appearance potentials have been determined for the 95.5 nm 2P→2P multiplets for all four target gases. The apparent cross sections, which include cascade contribution from higher states, were measured to range from 2 to 5×10−18 cm2 at 200 eV impact energy. The cross sections were found to be heavily influenced by 3p→3s cascading with contributions ranging from 30% (SF6) to 75% (CF4). Subtraction of the cascade contributions yielded direct cross sections of 0.5× 10−18 cm2 (CF4), 1.4×10−18 cm2 (CCl2F2), 1.5×10−18 cm2 (SF6), and 2.9×10−18 cm2 (NF3) at 200 eV. The fluorine emissions are the result of the total fragmentation of the parent molecule for the targets SF6, CF4, and NF3. A much lower appearance potential and a different energy dependence of the cross section in the case of CCl2F2 indicates that partial fragmentation of this molecule plays a very important role. The findings for the 97.5 nm 4P→2P multiplet were essentially similar to those for the 2P→2P multiplet with the exception that accurate apparent emission cross sections could not be determined from a measurement of the 97.5 nm photon emission intensity. Due to their longer lifetime an appreciable fraction of the excited fluorine (2p43s) 4P atoms was found to drift out of the viewing area of our detection system before decaying radiatively. An attempt was made to extrapolate values for the 97.5 nm 4P→2P cross sections at 200 eV from a detailed analysis of the near-threshold region of the cross section for SF6, CF4, and NF3 This approach yielded FI 4P →2P cross sections comparable in magnitude to the FI 2P→2P cross sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460348
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  • 8
    Electronic Resource
    Electronic Resource
    Absolute partial cross sections for the parent ionization of the CFx (x=1–3) free radicals by electron impact (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7868-7874 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report absolute partial electron-impact ionization cross sections from threshold to 200 eV for the formation of the parent CFx+ ions from the CFx free radicals (x=1–3). Fast (3–3.5 kV) beams of CF3, CF2, and CF radicals were prepared by near-resonant charge transfer of CF3+, CF2+, and CF+ with triethylamine (TEA), Xe, and NF3. The CF and CF3 neutral beams were found to contain primarily ground state neutral radicals with some evidence for the presence of a small amount of vibrational excitation (0.5 eV or less). Contributions to the CF2+ ion signal obtained at electron energies several electron volts below the 11.4 eV threshold for the ionization of ground state CF2 radicals indicate the presence of CF2 metastables (presumably in the 3B1 state) in the CF2 neutral beam. The level of CF2 metastable contamination was found to depend critically on the exact experimental conditions. At 70 eV, the absolute parent ionization cross sections are 0.38±0.07 A(ring)2 (CF3→CF3+), 1.03±0.16 A(ring)2 (CF2→CF2+), and 1.25±0.19 A(ring)2 (CF→CF+), respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464594
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  • 9
    Electronic Resource
    Electronic Resource
    Electron impact ionization of the SiDx (x=1–3) free radicals (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6315-6321 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of absolute cross sections for the electron-impact ionization and dissociative ionization of the SiDx (x=1–3) free radicals from threshold to 200 eV using the fast-neutral-beam technique. The deuterated rather than the protonated target species were used in order to allow a better separation of the various product ions from a given parent in our apparatus. A common feature of all three radicals studied in this work is a dominant parent ionization cross section with essentially the same absolute value of roughly 3.7×10−16 cm2 at 70 eV. Dissociative ionization processes for all three targets are less significant with a single dissociative process dominating in each case, viz. the removal of a single D atom (SiDx+e−→SiD+x−1+D+2e−). The cross section for this dominant dissociative ionization channel also had the same maximum value of about 1.2×10−16 cm2 for all three targets. A comparison of the experimentally determined total single ionization cross sections with calculated cross sections using a modified additivity rule showed good to satisfactory agreement for all three targets in terms of the absolute values, but reveals some discrepancies in the cross section shapes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472484
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  • 10
    Electronic Resource
    Electronic Resource
    Electron-impact ionization of the SO free radical (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 770-773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We studied the electron-impact ionization of the SO free radical using the fast-neutral-beam technique. Absolute cross sections were measured for the formation of the SO+ parent ion as well as for the S+ and O+ fragment ions from threshold to 200 eV. At 70 eV, cross section values of 3.25±0.50×10−20 m2 (SO+), 1.32±0.23×10−20 m2 (S+), and 0.45±0.08×10−20 m2 (O+) were obtained. We found little evidence of the presence of vibrationally excited SO radicals in the incident target beams and only negligible contributions to the measured ion signal from excited SO radicals in Rydberg and/or metastable states were observed. The only significant pathway contributing to the formation of the observed SO+, S+, and O+ ions is the single positive ion formation. The measured partial ionization cross sections were combined to yield the absolute total single ionization cross section of SO which was compared to calculations using a recently introduced modified additivity rule. The agreement between measured and calculated cross sections was found to be very good. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469190
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