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  • 1
    Electronic Resource
    Electronic Resource
    The vibrational distribution of the OH product from H2O photodissociation at 157 nm: Discrepancies between theory and experiment (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4119-4122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of H2O at 157 nm has been studied using the H atom Rydberg tagging time-of-flight technique. Vibrational state distribution has been measured for the OH product from H2O photodissociation. Comparisons with previous theoretical calculations and experimental results by laser-induced fluorescence (LIF) measurements have been made. The results in this work indicate that the relative populations for the high vibrationally excited OH(v[greater, double equals]2) products measured by the LIF technique are significantly underestimated, suggesting that LIF as a technique to quantitatively measure vibrational distributions of reaction product OH is seriously flawed. The experimental results presented here are in fairly good agreement with previous theoretical calculations, even though the calculated vibrational populations for the higher vibrational states of OH are still somewhat overestimated. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478293
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation of O2 at 157 nm: Experimental observation of anisotropy mixing in the O2+hν→O(3P)+O(3P) channel (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1758-1762 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, photodissociation of O2 at 157 nm has been studied using the photofragmentation translational spectroscopic technique. Two product channels O2+hν→O(1D)+O(3P), O2+hν→O(3P)+O(3P) have been observed. The relative yields and anisotropy parameters of both channels are determined. Anisotropy mixing of dissociation resulting from a perpendicular excitation and a parallel-type excitation has been observed in the dissociation channel O2+hν→O(3P)+O(3P). The observed results can be used to look at the detailed dynamical processes of the O2 dissociation through the Schumann–Runge band. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476751
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  • 3
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of OClO at 157 nm (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 10061-10069 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of OClO at 157.6 nm excitation has been investigated using the photofragment translational spectroscopic technique. Two distinctive chemical dissociation channels have been observed; one is the binary dissociation process, OClO+hν→ClO+O; the other one is the triple dissociation process, OClO+hν→Cl+O+O. The branching ratio of the binary dissociation channel to the triple dissociation channel is determined to be 0.59:0.41. Bimodal vibrational distribution of the ClO product has been observed for the OClO→ClO(X 2Π)+O(3P,1D) channel, implying that two distinctive dissociation routes possibly exist in the binary dissociation process. The bimodal distribution is likely caused by the two dissociation pathways from two excited electronic states: the D(2A1) and E(2B1) states of OClO. These arguments are further supported by the results of the anisotropy parameter measurements for the binary dissociation channels. Experimental results also show that the OClO+hν→ClO(X 2Π)+O(1S) and OClO+hν→ClO(A 2Π)+O(3P) channels might also exist in addition to the ClO(X 2Π)+O(3P,1D) channel. In the triple dissociation process, experimental results show that the main product channel is the OClO+hν→Cl(2P)+O(1D)+O(3P) channel, while the OClO+hν→Cl(2P)+O(3P)+O(3P) channel is the minor one. The branching ratio of these two channels is determined to be 0.89:0.11. From the modeling of the time of flight spectra of the O atom product, it is believed that the triple dissociation process of OClO is a simultaneous process within the time scale of one rotation period. Two-photon dissociative ionization process OClO+hν→Cl++O2+e− has also been observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476466
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  • 4
    Electronic Resource
    Electronic Resource
    Site and isotope effects on the molecular hydrogen elimination from ethylene at 157 nm excitation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2979-2982 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Site and isotope effects on the molecular hydrogen elimination from ethylene have been studied from the photodissociation of ethylene at 157 nm excitation. Experimental results show that there are three different types of molecular elimination processes: 1,1 elimination, 1,2-cis elimination, and 1,2-trans elimination. These elimination processes show significantly different translational energy distributions. Isotope effect on the dynamics of these molecular hydrogen elimination processes has been also investigated carefully. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476888
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  • 5
    Electronic Resource
    Electronic Resource
    New low background crossed molecular beam apparatus: Low background detection of H2 (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1642-1646 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low background and almost hydrocarbon free (∼1×10−14 Torr) molecular beam apparatus with an improved universal detector, based on electron bombardment ionization, has been constructed for crossed molecular beam research. Extremely high vacuum (∼1×10−12 Torr) for the detector's ionization region is achieved using multiple ultrahigh vacuum pumps. In addition to a home-made liquid nitrogen cryopump and a turbomolecular pump, a two stage cryogenic He cold head (∼10 K) is used to pump the detector's ionization region. Using this arrangement, the H2 background in the detector can be reduced by about two orders of magnitude in comparison with previously built similar instruments. Therefore, the signal-to-noise for detecting H2 product detection sensitivity is substantially enhanced, making experimental studies of H2 elimination channels in photodissociation processes much easier. Backgrounds at m/e=28 (CO+), 16 (CH4+,O+), 15 (CH3+), 14 (CH2+), and 13 (CH+) in the ionization detection region are also significantly reduced. In this article, we will describe the new apparatus in detail and present some preliminary results of the unimolecular decomposition studies of CH3OH at 157 nm excitation to demonstrate the capabilities of low background detection H2 using this new instrument. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148821
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  • 6
    Electronic Resource
    Electronic Resource
    Photodissociation of D2O at 121.6 nm: A state-to-state dynamical picture (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 7830-7837 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of D2O at 121.6 nm have been studied using the D atom Rydberg "tagging" time-of-flight technique. Product kinetic energy distributions and angular distributions have been measured. From these distributions, rovibronic distributions of the OD radical product and the rotational state-resolved angular anisotropy parameters have been determined. The dissociation energy D00 (D–OD) is determined to be 41912±20 cm−1. Alternations of population in the OD (X, v=0) rotational distribution, similar to those in the H2O photodissociation [S. A. Harich et al., J. Chem. Phys. 113, 10 073 (2000)] have also been observed, and thus are also attributed to dynamical interference between two conical intersection pathways. Very highly vibrationally excited OD (X) products (at least up to v=9) have also been observed, which is in accord with recent theoretical studies of H2O photodissociation by van Hemert et al. [J. Chem. Phys. 112, 5797 (2000)]. Evidence for the triple dissociation channel, O(3P)+2D, is also shown in this work. Branching ratios for the different product channels have been determined through simulations. Overall, the energy disposal among the products of D2O photodissociation at 121.6 nm is qualitatively similar to that for H2O, although the mass change leads to changes in the branching ratios. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1364683
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  • 7
    Electronic Resource
    Electronic Resource
    Photodissociation of H2O at 121.6 nm: A state-to-state dynamical picture (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10073-10090 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation dynamics of H2O at 121.6 nm have been studied using the H atom Rydberg "tagging" time-of-flight technique and by quasiclassical trajectory (QCT) calculations. Product kinetic energy distributions and angular distributions have been measured. From these distributions, rovibronic distributions of the OH radical product as well as the state resolved angular anisotropy parameters were determined. The dissociation energy D00(H–OH) is determined to be 41151±5 cm−1. Two clear alternations in the OH(X,v=0) rotational distribution have been observed, with each alternation corresponding to an oscillation in the anisotropy distribution. These oscillations had been attributed to the dynamical interference between the two conical intersection pathways. Further theoretical modeling in this work strongly supports this argument. Very highly vibrationally excited OH(X) products (up to v=9) have also been observed. These are ascribed to interconversion of H–O–H bending (H–H vibration) and O–H vibration in O–H–H geometries. The effect of parent rotational excitation on the OH(A) product state distribution and anisotropy distribution was observed for the first time. Experimental results also show clear evidence for the triple dissociation channel, O(3P)+2H. Accurate branching ratios of different product channels have been determined. Results of detailed QCT calculations agree well with the experimental results in this work. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1322059
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