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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8872-8876 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-resolved resonantly enhanced multiphoton ionization spectroscopy of I(2P3/2) and I(2P1/2) dissociation products of CF3I can be used to characterize populations of highly-excited CF3I*. This technique has been applied to monitor infrared multiphoton excitation dynamics of CF3I in the presence of collisions. Compared to collision-free situations, collisions tend to destroy bimodal vibrational energy distributions and to enhance the overall pumping rate. Collisional energy transfer could be monitored for molecules above the dissociation threshold. Collisional relaxation of highly-excited molecules has been followed and analyzed with respect to average energies transferred per collision.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8863-8871 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient detection of I(2P3/2) by resonantly enhanced multiphoton ionization (REMPI) was used to monitor in-pulse and after-pulse dissociation of CF3I excited by infrared (IR) multiphoton absorption. After-pulse reaction is characterized by time-dependent dissociation rate coefficients. The apparent reaction rates increase with increasing laser intensity. These observations are attributed to strong rotational dependencies of the specific dissociation rate constants k(E,J) and to CO2 laser-intensity-dependent rotational distributions of the excited CF3I. The corresponding rotational distributions are reconstructed from the observed experimental time profiles of the reaction rates. In addition to the detection of the I(2P3/2) dissociation product from infrared multiphoton excitation, populations of vibrationally highly excited CF3I* were identified via electronic excitation in the visible, subsequent fast dissociation and REMPI detection of the resulting I(2P1/2). At weak IR laser intensities these vibrational distributions were found to be strongly bimodal. However, the bimodal character weakens with increasing laser intensity, tending towards a single broad distribution at very high laser intensities.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 890-899 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient UV absorption spectra of CF3I were recorded during the IR multiphoton excitation of this molecule. Short laser pulses (20–50 ns) without longer tails were employed. Pressure effects were analyzed in the 10–100 mTorr range. Unimolecular dissociation rates (in the 106–107 s−1 range) after the pulse were identified unambiguously by time-resolved low-pressure observations and collisional quenching experiments. Marked laser intensity effects on the rates are attributed to intensity-dependent changes of rotational state distributions of the reacting molecules. Excited state distributions have been resolved in direct observations. Bimodal distributions were identified.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 900-905 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy transfer of vibrationally highly excited CF3I molecules (E(approximate)18 000 cm−1) in collisions with argon, propane, and octane was studied using hot UV absorption spectroscopy of CF3I. the preparation of the excited CF3I was achieved by IR multiphoton absorption which, under the conditions applied, produces a narrow initial energy distribution of CF3I near to the dissociation energy. The average energies 〈ΔE〉 transferred per collision were found to be proportional to E for the bath gases propane and octane; they showed a stronger increase with energy at low excitation energies in the bath gas argon. The energy dependence of 〈ΔE〉, therefore, is not only governed by the properties of the excited molecule (e.g., its density of states) but also by features of the collision partner (e.g., the magnitude of 〈ΔE〉). At energies near to the dissociation energy for all colliders, 〈ΔE〉 was found to approach values similar to those obtained from single UV photon excitation experiments with highly excited triatomic and large polyatomic molecules.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8885-8898 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the technique of double-resonance overtone photofragment spectroscopy (DROPS), we have measured rotationally resolved vibrational overtone transitions to the previously unobserved 5v1, 6v1, and 7v1 levels of gas-phase trans-nitrous acid (HONO) in its electronic ground state. Observing the onset of dissociation from different rovibrational states of 5v1 near threshold determines the HO–NO bond energy to be D0=16 772±14 cm−1. Observed spectral splittings and broadening of individual rovibrational transitions provide quantitative data on the rate and extent of collision free vibrational energy redistribution that would result after coherent ultrashort pulse excitation. In parallel with these frequency domain measurements, we determine the unimolecular dissociation rates directly in time for trans-HONO molecules excited to several rotational states near threshold. The combination of time- and frequency-resolved data allows us to estimate the linewidth contributions from the finite dissociation lifetime of the molecule. Our results reveal intramolecular dynamics that are clearly not a simple function of the vibrational energy but rather depend sensitively upon specific couplings and, in turn, on the vibrational character of the individual states excited. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6522-6530 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of rotational excitation on the specific rate constants k(E,J) of the unimolecular decomposion of NO2 has been investigated. Time-resolved pump- and probe experiments with sub-ps time resolution are reported in which NO2 molecules with well-defined rotational and vibrational energy distributions were optically excited near and above the dissociation threshold. The subsequent unimolecular decay of the reacting NO2 molecules was probed by time-resolved laser-induced fluorescence of the disappearing NO2 via excitation to Rydberg states. At constant photolysis wavelength, increasing rotational energy (up to 310 cm−1) was found to leave the overall decay rate nearly unaffected. This observation can be rationalized by assuming a compensation of the angular momentum and energy dependences of the specific rate constants when J and E are changed at the same time. Keeping the total energy E nearly constant and changing J independently, the effect of rotation on the decay rate can be separated and observed more clearly. From the experimental data we conclude that, for sufficiently high J and constant total energy, molecules with larger J dissociate more slowly than molecules with small J, which is in agreement with predictions from statistical unimolecular rate theory. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6531-6537 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optical double-resonance "fluorescence depletion pumping," has been employed to investigate rovibronic states of jet-cooled NO2 in the region of the dissociation threshold E0. The method allows for the selection of angular momenta of the reacting molecules. In particular, molecules with J=0.5 and 1.5 or with J=2.5 and 3.5 have been selectively investigated. In the first 10 cm−1 above E0, the linewidths for J=0.5 and 1.5 as well as 2.5 and 3.5 have been found to fluctuate around average values which correspond to dissociation rate constants of 2×1010 s−1 and 1.65×1010 s−1, respectively. The experimental results for J=0.5 and 1.5 are in agreement with time-resolved data and quantum mechanical calculations. The difference in average linewidths for the molecules with J=0.5/1.5 and 2.5/3.5 was found to be small. The appearance of the double-resonance spectra does not principally change for higher angular momentum J, i.e., some sharp lines on top of a congested unresolved background are still observed. It is concluded that the dependence of the average lifetimes on J in the present low J-experiments very close to the dissociation threshold is only weak and hardly detectable, which appears to be consistent with recent measurements in the time domain. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9681-9690 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The competition between C–Br–bond fission and three-center elimination of molecular bromine (Br2) in highly excited CF2Br2 molecules has been studied under collision-free conditions. Transient resonantly enhanced multiphoton ionization (REMPI) was used to monitor Br(2P1/2) and Br(2P3/2) formation during and after infrared (IR) multiphoton excitation of CF2Br2; time-resolved laser-induced fluorescence (LIF) spectroscopy was employed for the detection of transient CF2 after Br2 elimination. Direct time-resolved measurements of the sum of afterpulse reaction rates, absolute product yields for the CF2 and Br(2P3/2) channels as well as absorbed energies per excitation pulse were used to characterize parts of the vibrational energy distribution P(E) established after IR multiphoton excitation and to determine rate coefficients and branching ratios for the elimination and dissociation reaction as a function of the average internal energy 〈E〉. The existence of both channels, the dissociation and the elimination channel, has been confirmed. A comparison of the experimental data with statistical adiabatic channel model calculations (SACM) enabled us to determine the threshold energies E0(J=0) for the unimolecular Br2 elimination [E0(J=0)=19 070±500 cm−1] and the C–Br bond fission [E0(J=0)=20 700±500 cm−1], the two possible pathways of the reaction. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    British journal of dermatology 102 (1980), S. 0 
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Calcification of the penis, whether in the skin, subcutaneous tissue or corpora is exceedingly rare and is usually secondary to trauma or Peyronie's disease. A case of idiopathic calcinosis cutis of the penis is presented.
    Type of Medium: Electronic Resource
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