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  • 1
    Electronic Resource
    Electronic Resource
    Planar laser-induced fluorescence imaging of Cu atom and Cu2 in a condensing laser-ablated copper plasma plume (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5095-5107 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Planar laser-induced fluorescence (PLIF) is used to monitor Cu atoms and Cu2 produced by excimer laser ablation of a copper target (308 nm, (approximately-greater-than)10 J/cm2, 1–3 GW/cm2) expanding rapidly into helium background gas at pressures ranging from 10 to 100 Torr. The Cu2 results from gas phase condensation of the copper atoms ablated from the target in the regions of highest Cu atom density as expected, but the maximum Cu2 laser-induced fluorescence (LIF) signal occurs significantly after the maximum of the Cu signal. Rotationally resolved excitation scans of Cu2 utilizing the A–X (0,0) transition indicate that the Cu2 has reached equilibrium with the 300 K background gas. An extensive search for Cu3 via LIF failed, indicating that Cu3 is present only in very low "steady state'' number density in the plume. This data is explained qualitatively by a simple kinetic model. In addition to the kinetic information, it is clear from the PLIF images that viscous eddy formation becomes more pronounced as the backing gas pressure increases; however, we see no evidence of turbulence in the plume even at the highest backing gas pressure studied. The PLIF technique allows us to observe the onset of condensation directly as well as to obtain information about the expansion dynamics of the plume not easily obtainable by other means.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352039
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  • 2
    Electronic Resource
    Electronic Resource
    Erratum: Laser-induced fluorescence of the B 2Σ+–X 2Πi system of OH: Detection of v‘=8 and 9 [J. Chem. Phys. 90, 3484 (1989)] (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 818-818 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458631
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  • 3
    Electronic Resource
    Electronic Resource
    Cu+2 vibronic states at 0–1.4 eV from multiphoton ionization–photoelectron spectroscopy (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5243-5245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used resonant two-photon ionization (R2PI) of cold Cu2 in a pulsed molecular beam in conjunction with time-of-flight photoelectron spectroscopy (TOF-PES) to study the vibronic states of Cu+2 from 0–1.4 eV. The Cu+2 threshold of 7.899±0.005 eV agrees with the ionization energy previously inferred from R2PI spectral intensities. We cleanly resolve a pair of Cu+2 excited state vibrational progressions with origins at 1.143 and 1.256 eV above threshold; both have ω+e=252±17 cm−1. We assign these progressions as a 3d-hole, 2Π spin–orbit pair. In addition, in the range 0–1 eV, we observe a dense set of at least 50 moderately well-resolved bands which can be fit to a single progression with ω+e=187±8 cm−1 and ωex+e=0.7±0.2 cm−1. While this might be the anticipated 2Σ+g ground state, the intensity pattern (multipeaked envelope, with alternation of intensities in some regions) suggests the possibility of multiple low-lying 3d-hole electronic states of Cu+2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454577
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  • 4
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence in the B˜–X˜ system of the HCO radical (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7601-7608 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectroscopy of the B˜ 2A'–X˜ 2A' system of the formyl radical has been studied by laser-induced fluorescence. HCO was generated by photolysis of acetaldehyde, and a tunable laser operated near 245 nm excited eight bands of B˜–X˜. The (0,0,2)–(0,0,0) band has been rotationally analyzed, yielding A'=14.46 cm−1 and (B'+C')/2=1.13 cm−1 for this slightly asymmetric top; asymmetry splitting and spin doubling are observed. The intense branches have ΔK=0 but there also are weaker perpendicular components with the transition moment near the b axis. Vibronic transition energies agree with those from matrix absorption but with a 130 cm−1 blueshift. Resolved fluorescence spectra to X˜ levels as high as 15 000 cm−1 furnish vibrational constants for the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459391
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  • 5
    Electronic Resource
    Electronic Resource
    Vibronic structure of TiO+ from multiphoton ionization photoelectron spectroscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1415-1428 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the techniques of resonance enhanced multiphoton ionization (REMPI) and time-of-flight photoelectron spectroscopy (TOF-PES) to TiO molecules cooled in a pulsed nozzle expansion to obtain vibronic spectra of gas phase TiO+. The adiabatic first ionization energy is refined to I1(TiO)=54 999±52 cm−1=6.819±0.006 eV, which yields D0(Ti+–0) =159.9±2.2 kcal/mol. For the X 2Δ state of TiO+, we resolve spin–orbit pairs of vibrational levels for v=0–14, yielding ωe=1045±7 cm−1 and ωexe =4±1 cm−1. The spin–orbit splitting ΔEso =210±6 cm−1 permits confirmation of the state symmetry by comparison with the known spin–orbit splittings of the X 3Δ state of TiO. We also observe a new excited B 2∑+ state at T0=11 227±17 cm−1 with ωe =1020±9 cm−1 and ωexe =6±2 cm−1. This state is distinct from the A 2∑+ state (average frequency 860±60 cm−1) previously observed by Dyke and co-workers. From components of certain PESs apparently due to one or more metastable states of TiO, we infer the existence of a previously unobserved state of neutral TiO at T0=2980 cm−1, possibly the 3∑− state. Finally, we discuss the electronic structure and vibrational frequencies of TiO, TiO+, and other third row metal oxides from both molecular orbital and ligand field points of view in order to understand the ordering of electronic states and certain trends in vibrational frequencies. The molecular orbital model readily explains why nominally isoelectronic neutral and cationic metal oxides, such as TiO+ and ScO, are electronically quite dissimilar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456083
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  • 6
    Electronic Resource
    Electronic Resource
    Collision dynamics of OH(X 2Πi,v=12) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5741-5746 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional removal rate constants for the OH radical in v=12 of the ground electronic state are measured for the colliders CO2, O2, N2, H2, He, and Ar. OH molecules, generated in v=8 by the reaction of hydrogen atoms with ozone, are excited to v=12 by direct overtone excitation with pulsed infrared laser light. The temporal evolution of the v=12 radicals is probed as a function of collider gas pressure by a time-delayed pulsed ultraviolet probe laser. The probe laser is used to excite the molecules via the B 2Σ+–X 2Πi(0,12) electronic transition, and the resulting B 2Σ+–A 2Σ+ fluorescence is detected. We measure rate constants for CO2:(5.6±1.5)×10−11; O2:(1.6±0.2)×10−11; He:(3.6±0.6)×10−12; H2:(3.0±0.8)×10−12; Ar:(2.6±0.5)×10−12; N2:(2.5±0.7)×10−12 (all in units of cm3 s−1). These rate constants are over fifty times faster in all cases than the vibrational relaxation rate constants for the lower levels (v=1 and v=2) of the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459567
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  • 7
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence of the B 2Σ+–X 2Πi system of OH: Detection of v''=8 and 9 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3484-3489 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The previously unobserved B 2Σ+–X 2Πi electronic system of OH is detected by laser-induced fluorescence in a low-pressure flow system. OH is produced in high vibrational levels of the ground electronic state by the H+O3 reaction. Light from a frequency-doubled tunable dye laser excites the radical via the (0,8), (0,9), and (1,8) bands of the B 2Σ+–X 2Πi transistion at 225, 236, and 221 nm, respectively. The fluorescence is detected in the B 2Σ+–A 2Σ+ system in the visible and near ultraviolet. Measured emission intensities in the (0,3) to (0,9) and the (1,3) to (1,9) bands of B–A are in good agreement with previous theoretical calculations. The experimental branching ratio for emission between the B–A (0,3) and B–X (0,10) bands is about three times larger than theoretically predicted. Detection of high-lying vibrational levels in the electronic ground state, v''=6 through 15, for experiments in collision dynamics and reaction kinetics, is feasible using the B–X system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455858
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  • 8
    Electronic Resource
    Electronic Resource
    Resonant two-photon ionization-photoelectron spectroscopy of Cu2: Autoionization dynamics and Cu+2 vibronic states (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3854-3868 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonant two-photon ionization of gas phase Cu2 in a cold molecular beam in conjunction with time-of-flight photoelectron spectroscopy provides new vibronic state spectroscopic information for the dimer cation Cu+2. One color ionization via the 0–0, 1–0, and 2a–0 bands of Smalley's System V neutral Cu2 resonant states (J←X transition) accesses Cu+2 states in the range 0–1.4 eV. The electron kinetic energy measurements slightly refine the first adiabatic ionization energy of Cu2 to I1(Cu2)=7.899±0.007 eV. We observe two electronic states of Cu+2 which we assign as X 2Σ+g and an excited 2Π spin–orbit pair of sublevels with origins at T0(2Π3/2)=1.143±0.002 eV and T0(2Π1/2)=1.256±0.002 eV. The absence of spin–orbit splitting identifies the ground state 2Σ symmetry; the spin–orbit splitting of 898±8 cm−1 identifies the excited states as 2Π. Within X 2Σ+g we observe a remarkably long vibrational progression, perhaps extending from v=0–80. The vibrational intervals determine the constants ωe=188±4 cm−1 and ωexe=0.75±0.09 cm−1. The 2Π vibrational intervals determine ωe=244±6 cm−1. The adiabatic bond dissociation energy of ground state Cu+2 is D0(Cu+–Cu)=1.84±0.08 eV. The intensity pattern of the X 2Σ+g vibrational bands exhibits multiple peaks whose positions and amplitudes are sensitive to the resonant J state vibrational level. For 0–0 excitation, we observe reproducible band intensity alternation. We present preliminary mass spectral and photoelectron data indicating that the cause of the highly non-Franck–Condon band intensities is excitation of long lived, dissociative autoionization states which undergo extensive nuclear motion on the time scale of electron ejection. We propose an autoionization mechanism that includes a description of the Cu2 J state and explains the observed phenomena invoking only one electron transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456870
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  • 9
    Electronic Resource
    Electronic Resource
    Limitations in the application of hook spectroscopy for density measurement in high-density-gradient media (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7576-7578 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hook spectroscopy has been successfully implemented to measure ground-state Cu atom density in laser-ablated copper vapor plumes in a background gas. In 1–25 Torr of background gas, the technique has been used to measure Cu atom densities up to 4×1015 cm−3. With higher background gas pressures, increasing distortion of the hook spectra is observed until they are rendered nearly uninterpretable at background gas pressures as low as 100 Torr. This effect is attributed to wavelength-dependent beam deflection caused by large gradients in copper atom density present at high background gas pressures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356587
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  • 10
    Electronic Resource
    Electronic Resource
    Detection of Cl in rf plasmas by laser-excited stimulated emission (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1182-1184 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-excited stimulated emission is used to detect chlorine atoms in a Cl2/Ar rf etching plasma. Two laser photons near 233.3 nm excite the 3p44p 4S0 electronic state of atomic chlorine in a spin-forbidden transition from the 3p5 2P0 ground state. At modest laser fluence stimulated emission is observed from the 3p44p 4S0→3p44s 4P transition. The stimulated emission signals are compared to simultaneously acquired laser-induced fluorescence from the same transition. The strong, collimated stimulated emission provides a means to detect atomic chlorine which only requires a single optical access window.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102260
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