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  • 1
    Electronic Resource
    Electronic Resource
    Modulation of resonant multiphoton ionization of CH3I by laser phase variation (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 826-831 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phase control of molecular absorption, first proposed by Shapiro, Hepburn, and Brumer was accomplished with CH3I using the technique of Chen, Yin, and Elliott. Red light (λ near 603 nm) was focused in a cell containing CH3I gas at a pressure around 1 Torr. The emerging light, a coherent mixture of the fundamental and the third harmonic (λ near 201 nm), was refocused on a molecular beam of CH3I and multiphoton ionization was detected. Ionization was by two simultaneous processes: a uv photon absorption followed by the absorption of two red photons (1+2 process) and an absorption of three red photons followed by the absorption of two more (3+2 process). Because of the sharp resonant Rydberg transition at 201 nm, the one and three photon matrix elements dominate the transition. Interference between the amplitudes of these two paths was demonstrated by varying the pressure and, hence, the index of refraction of the Ar gas in a tuning cell where the two light beams were refocused by two spherical mirrors. The modulation depth varied with wavelength but had a maximum of 75%, the largest modulation so far observed in this kind of experiment. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470808
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  • 2
    Electronic Resource
    Electronic Resource
    The reaction of Cs(82P) and Cs(92P) with hydrogen molecules (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1338-1343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactions of Cs(n2PJ), n=8, 9, J=1/2, 3/2 with H2 were studied by laser induced fluorescence of the nascent product. No difference was found in the reactivity of the J=1/2 and 3/2 states. The energies available to the reaction products were 11.5 and 16.9 kcal/mol for the n=8 and 9 states, respectively. CsH was found in the v=0 and 1 states but could not be detected in any higher vibrational state. The v=0/v=1 population ratios were 1/0.33 (n=8) and 1/0.42 (n=9). The products rotational temperatures were approximately the same as the ambient temperature of the reaction cell. Thus about 90% of the available energy is released as translation. From these data the following picture is derived. The mechanism is a primarily collinear abstraction and not an insertion. The large translational energy release is caused by a sudden switching on of repulsion when the H atoms are still close to each other. The reaction involves electron transfer, but at Cs–H distances not far from the equilibrium bond length and is therefore not a harpoon reaction in the usual sense. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470790
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  • 3
    Electronic Resource
    Electronic Resource
    Phase control of absorption in large polyatomic molecules (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2992-2997 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phenomenon of interference of the amplitude for absorption of one photon of frequency 3ω and the amplitude for absorption of three photons of frequency ω was theoretically predicted by Shapiro, Hepburn, and Brumer. The interference was demonstrated experimentally by varying the relative phase between the tripled frequency photon and three photons with the fundamental frequency by the groups of Elliott and Gordon in atoms and small molecules. In order to see how general this phenomenon is, five compounds were studied, ammonia, trimethylamine, triethylamine, cyclooctatetraene, and 1,1-dimethylhydrazine. CH3I was used as the tripling gas for light in the range 604–600 nm. Interference was observed in all cases. The last four compounds have low ionization potentials and interference was observed between a 3+1 and a 1+1 ionization process with a maximum modulation of 22%. NH3 with a higher ionization potential requires absorption of 3+2 or 1+2 photons and exhibits a maximum modulation of 33%. We conclude that molecular size is no obstacle and that as long as a molecule has sufficiently strong absorption at the tripled frequency, and sufficient vapor pressure, and the laser fundamental beam is very strong, phase control of interference is observable. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472172
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  • 4
    Electronic Resource
    Electronic Resource
    Reactions of O(3P) with alkynes: The CO and H atom channels (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 488-495 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This is the second in a series of papers on the reaction of O(3P) with alkynes in which the internal state distribution of some products are studied. The first paper dealt with acetylene whose two product channels are CO+CH2 and H+HCCO. The present paper deals with the reactions of a series of higher alkynes; however, just the CO release and the H atom release channels were studied. The CO product was rotationally and vibrationally cold in every case. We therefore infer that, except possibly for acetylene, the initial ketocarbene undergoes intersystem crossing to a singlet state and isomerizes to a substituted ketene which then dissociates through a linear C–C–O transition state. The absence of CO vibration energy implies that the energy taken from the initially formed C–O bond to facilitate a 1,2 migration is not returned. The large H atom translational energy implies that the H atom is released simultaneously with the formation of a radical of high resonance energy. Finally, the CO and H atom yields decrease in the longer alkynes, presumably because the dominant reaction channel becomes C–C bond breaking leading to radical pair formation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471902
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