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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adiabatic ionization potential of methylene has been determined to be 83772±3 cm−1 from a rotationally resolved photoelectron spectroscopic study of the CH2+ X˜ 2A1 (0,0,0)←CH2 X˜ 3B1(0,0,0) transition. This value was used to determine thermochemical quantities such as the 0 K dissociation energy of the ketene cation in CO and CH2+ D0(CH2(Double Bond)CO+)=33202±7 cm−1, the 0 K dissociation energy of the methyl radical D0(CH2–H)=38179±49 cm−1, the 0 K dissociation threshold of methane in CH2 and H2 D0(CH2–H2)=38232±50 cm−1 and the 0 K enthalpy of formation of CH2 ΔfH(minus sign in circle)(CH2,T=0 K)=390.73±0.66 kJ mol−1. © 2002 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9840-9851 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of Kr2 has been recorded between 103 500 cm−1 and 118 000 cm−1. Photoelectronic transitions to four [the I(1/2u), I(3/2u), II(1/2u), and II(1/2g) states] of the first six electronic states of Kr2+ have been observed. The photoelectronic transition to the ground I(1/2u) state consists of a long progression of vibrational bands, starting at v+=0. From the resolved isotopic substructure of vibrational levels with v+≥15, the absolute numbering of the vibrational quantum number could be determined. The analysis of the spectrum has led to improved values of the adiabatic ionization potential [IP(I(1/2u))=(103 773.6±2.0) cm−1], the dissociation energy [D0+(I(1/2u))=(9267.8±2.8) cm−1] and to the determination of an analytical potential energy curve that reproduces the experimental data from v+=0 to beyond 81% of the dissociation energy. The transitions to vibrational levels of the I(1/2u) state with v+≤30 and v+≥65 have vanishing Franck–Condon factors for direct ionization from the ground neutral state and gain intensity from transitions to low Rydberg states that belong to series converging on excited electronic states of Kr2+. In the region immediately below the first dissociation limit of Kr2+, a second progression was observed and assigned to a photoelectronic transition to the I(3/2u) state. The adiabatic ionization potential [IP(I(3/2u))=(112 672.4±2.0) cm−1], the dissociation energy [D0+(I(3/2u))=(369.1±2.8) cm−1] and vibrational constants could be extracted for this state. Two further progressions were observed below the second dissociation limit of Kr2+ and assigned to transitions to the II(1/2u) and II(1/2g) states. The adiabatic ionization potentials [IP(II(1/2u))=(117 339.7±2.0) cm−1, IP(II(1/2g))=(117 802.6±2.0) cm−1] and the dissociation energies [D0+(II(1/2u))=(1071.7±2.8) cm−1, D0+(II(1/2g))=(608.8±2.8) cm−1] were determined for these two ionic states. In the region just below the ionic dissociation limits, artifact lines are observed in the PFI-ZEKE photoelectron spectra at the position of transitions to Rydberg states of the krypton monomer. At the lowest threshold, collisional and associative ionization of the long lived atomic Rydberg states leads to the formation of ZEKE electrons; at the upper threshold, the rapid autoionization of the atomic Rydberg states forms high ion concentrations, and the electrons that remain trapped in the ion cloud are released by the delayed pulsed field used to produce and extract the PFI-ZEKE electrons. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 157-159 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The upper energy limit of broadly tunable coherent radiation sources based on resonant four-wave mixing is investigated. An argon resonance [the two-photon (3p)54p[5/2](J=2)←(3p)6 resonance at 10 5617 cm−1] has been used in resonant four-wave mixing to generate tunable coherent narrow-bandwidth extreme ultraviolet radiation. With this resonance, spectroscopically useful laser intensities (up to 5×106 photons per laser pulse) can be produced beyond 19 eV with a bandwidth as low as 0.1 cm−1. The light source is used to record a pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of the b 4Σg−(v+=1)←X 3Σg−(v=0) photoelectronic transition of O2. © 1998 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9762-9771 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pulsed-field-ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar2 has been recorded between 116 500 cm−1 and 128 200 cm−1. The spectrum consists of a long progression of transitions to the vibrational levels of the ground A 2Σ1/2u+ state of Ar2+ with v+ up to 52, a shorter progression of four bands attributed to transitions to the first four vibrational levels of the C 2Π1/2u state and of a single sharp line assigned to the C 2Π3/2u(v+=0)←X 10g+(v=0) transition. Rotational constants of several vibrational levels of the A 2Σ1/2u+ state have been determined from high resolution PFI-ZEKE photoelectron spectra. From these measurements new information on the first electronic states of Ar2+ has been extracted. An analytical potential energy function has been derived for the A 2Σ1/2u+ state which extends to large internuclear distances (beyond 5 Å) and reproduces all measured vibrational energy levels up to v+=52. The adiabatic ionization potential for the photoelectronic transitions to the A 2Σ1/2u+, C 2Π3/2u and C 2Π1/2u states are determined to be 116 591.1±6 cm−1, 126 883.9±3 cm−1 and 128 004.1±5 cm−1, respectively, from which dissociation energies (D0+) of 10 603.7±6 cm−1, 310.8±3 cm−1, and 622.5±5 cm−1 are obtained. The vibrational levels of the C 2Π1/2u state can be described by a Morse potential with ωe=58.9±0.8 cm−1 and ωexe=1.40±0.27 cm−1, respectively. Associative ionization and collisional ionization processes involving argon atom Rydberg states induce spurious peaks in the PFI-ZEKE photoelectron spectrum. Ways to unambiguously identify these spurious peaks are discussed. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10819-10822 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar2 has been recorded between 116500 and 128500 cm−1. The spectrum consists of a progression of 52 vibrational bands in the A 2Σ1/2u+←X 1Σg+ (X 10g+ in Hund's case (c) notation) photoelectronic transition. The absolute numbering of the vibrational progression in the A←X transition is achieved by measuring the isotope shifts of two vibrational bands of the 36Ar2 molecule. From the analysis of the vibrational progression the first adiabatic ionization potential of Ar2 has been determined to be 116593.5±6.0 cm−1 (14.4558±0.0007 eV) from which a dissociation energy D0 of 10601.2±6.0 cm−1 (1.3144±0.0007 eV) results for the A 2Σ1/2u+ ground state of Ar2+. The potential curve of the ground ionic state in the vicinity of the potential minimum is adequately represented by a Morse potential with ωe+=307.0±0.4 cm−1 and ωexe+=2.05±0.05 cm−1. The position of higher members of the vibrational progression with v+>25 cannot be fitted accurately with a Morse potential. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6523-6533 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution zero-kinetic-energy photoelectron spectroscopy has been used to record the transition between the lowest bound state (3s 2A1) of the perdeuterated ammonium radical (ND4) and the X˜ 1A1 ground vibronic state of the perdeuterated ammonium ion (ND4+). The spectra obtained are the first rotationally resolved photoelectron spectra ever measured for a tetrahedral molecule. The analysis of the rotational structure is accompanied by a description of the observed symmetry selection rules and propensity rules for core rotational angular momentum changes that characterize the photoionization process. Rotational constants (B0=2.8560±0.0037 cm−1 and B0+=2.9855±0.0037 cm−1) and centrifugal distortion constants (D0=(4.78±1.4)×10−5 cm−1 and D0+=(4.77±1.5)×10−5 cm−1) have been determined for the 3s 2A1 state of ND4 and the X˜ 1A1 state of ND4+, respectively. The ionic rotational constant is in good agreement with the value B0+=2.9787±0.0029 cm−1 determined indirectly by Crofton and Oka (J. Chem. Phys. 86, 5983 (1987)) from the measurement of allowed transitions of the ν3 vibrational band of ND4+. The neutral rotational constant differs markedly from the ab initio value B0=3.0407 cm−1 of Havriliak and King (J. Am. Chem. Soc. 105, 4 (1983)) used by Alberti, Huber and Watson (J. Mol. Spectrosc. 107, 133 (1984)) as input data to fit the rotational structure of the Schüler band of ND4. The adiabatic ionization potential of ND4 is determined to be 37490.7±1.5 cm−1 (4.64826±0.00019 eV). The large changes in core rotational angular momentum that accompany the removal of the photoelectron may be caused by the Cooper minimum in the s→p photoexcitation/photoionization channel recently predicted by Smith and Chupka [Chem. Phys. Lett. 250, 589 (1996)] to lie in the vicinity of the ionization threshold. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 950-961 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The decay dynamics by predissociation and rotational autoionization of high Rydberg states of HD close to the first few rotational levels of the ground vibronic state of the HD+ cation have been studied by delayed pulsed field ionization following resonant (1+1′) two-photon absorption via the B state. Although predissociation and autoionization both contribute to the rapid decay of Rydberg states with principal quantum number n(very-much-less-than)100, the highest Rydberg states (n(approximately-greater-than)100) are stable for more than 20 μs. In contrast to H2, channels associated with an HD+ (v+=0, N+=even) ion core are coupled to channels associated with an HD+ (v+=0, N+=odd) ion core. We demonstrate that complex resonances that arise from rotational channel interactions between low (n∼25) Rydberg states characterized by a core with rotational angular momentum quantum number N++2 and the pseudocontinuum of very high Rydberg states characterized by an N+ core can be used with high efficiency to produce long-lived high Rydberg states. An investigation of the pulsed field ionization characteristics of these complex resonances enables us to measure the branching between diabatic and adiabatic field ionization and to determine the optimal conditions required to extend the method of H-photofragment Rydberg translational spectroscopy pioneered by Schnieder et al. [J. Chem. Phys. 92, 7027 (1990)] to molecular species. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4509-4518 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The decay dynamics of the high Rydberg states of N2 converging on the first few rotational levels (N+=0,1,2,3) of the ground vibronic X 2Σ+g (v+=0) state of the N+2 cation have been investigated by delayed pulsed field ionization (PFI) following two-photon enhanced (2+1′) three-photon excitation via the a″ 1Σ+g (v′=0) state of N2. The experiments were carried out in the presence of a weak homogeneous dc electric field and at typical ion densities of 200–2000 ions/mm3. All Rydberg states in the range of principal quantum number n=140–200 exhibit extreme stability against autoionization and predissociation and some have lifetimes which exceed 30 μs. The decay of the highest Rydberg states beyond n=200 is induced by external perturbations (field ionization and collisional ionization) and no Rydberg states beyond n=350 can be observed by delayed PFI. The Rydberg states which converge on the N+=0 and 1 rotational levels of the ion, and which therefore are not subject to rotational autoionization, decay into neutral products (by a process presumed to be predissociation) in less than 7 μs in the range n<100. The importance of predissociation is greatly reduced beyond n=100 and becomes negligible on our experimental timescale (30 μs) above n=140. The decay of the Rydberg states converging on the N+=2 and 3 rotational levels of the ion is more complex. Below n=100, only 30%–40% of the Rydberg population decays by fast rotational autoionization whereas 60%–70% decays by predissociation.The importance of predissociation decreases rapidly above n=100 and becomes negligible beyond n=140. The decay by rotational autoionization can be observed at all n values but becomes noticeably slower beyond n=100. In the range n=140–200 it exhibits a marked biexponential decaying behavior with 30% of the population decaying within a few microseconds and 70% displaying long term stability (τ(approximately-greater-than)30 μs). The branching between predissociation and autoionization is explained by the effect of the dc electric field which mixes strongly the optically accessible p Rydberg series with the high l manifold beyond n=100. The long lifetimes observed experimentally indicate that ml mixing becomes important as soon as l mixing sets in. © 1995 American Institute of Physics.
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  • 9
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 10033-10045 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Very high resolution spectra of high Rydberg states of the argon atom with principal quantum numbers in the range n=60–200 have been measured in double-resonance experiments using a high resolution vacuum ultraviolet laser and frequency stabilized millimeter waves. The 250 kHz resolution achieved in the double-resonance spectra enables the determination of accurate effective quantum numbers and the precise measurement of fine-structure intervals in l=0–3 Rydberg states at n values much beyond 50. The high resolution is also used to detect spectral shifts induced by small electric fields. Analysis of these spectral shifts allows the determination of stray electric fields with uncertainties of less than 1 mV/cm and their compensation to less than 1 mV/cm. The spectra of high Rydberg states are very strongly influenced by experimental conditions and the highest resolution can only be obtained when the stray electric fields are reduced to less than 1 mV/cm and the intensity of the millimeter waves are reduced to much less than 1 μW/cm2. High resolution measurements on the very high Rydberg states probed by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy are also reported. These spectra are strongly influenced by the inhomogeneous electric field of ions and other Rydberg states located in the photoexcitation region. These fields induce a strong mixing of the optically accessible low-l Rydberg states with nonpenetrating high-l Rydberg states. These results conclusively demonstrate the important role played by ions in PFI-ZEKE spectroscopy. © 1998 American Institute of Physics.
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