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  • 1
    Electronic Resource
    Electronic Resource
    Correlation of tryptophan fluorescence intensity decay parameters with proton NMR-determined rotamer conformations: [tryptophan2]oxytocin (1992)
    s.l. : American Chemical Society
    Biochemistry 31 (1992), S. 1585-1594 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00121a002
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  • 2
    Electronic Resource
    Electronic Resource
    Competition between photochemistry and energy transfer in ultraviolet-excited diazabenzenes. II. Identifying the dominant energy donor for "supercollisions" (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5844-5851 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: CO2 bath molecules scattered into J=72 of the 0000 vibrational state at short times after 248 or 266 nm UV excitation of pyrazine are probed using high resolution time resolved IR diode laser spectroscopy as a function of UV laser fluence from ∼3 to 80 mJ/cm2. The implications of pyrazine photodissociation for the interpretation of these collisional energy transfer experiments are considered. Specifically, the possibility that translationally hot HCN resulting from pyrazine dissociation may be the source of excitation for collisions that impart a large amount of rotational and translational energy to CO2 molecules is examined. Transient absorption measurements probing rotationally and translationally excited CO2 molecules produced following excitation of pyrazine are analyzed within the context of a kinetic scheme incorporating pyrazine photodissociation, as well as excitation of CO2 by both translationally hot HCN and vibrationally excited pyrazine. This analysis indicates that vibrationally hot pyrazine, which has sufficient energy to dissociate, is the source of excitation in collisions imparting large amounts of rotational and translational energy to CO2. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481158
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  • 3
    Electronic Resource
    Electronic Resource
    Long- and short-range interactions in the temperature dependent collisional excitation of the antisymmetric stretching CO2(0001) level by highly vibrationally excited pyrazine (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6682-6695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relaxation of highly vibrationally excited pyrazine, C4H4N2, by collisions with CO2 that produce molecules in the vibrationally excited antisymmetric stretch state (0001) has been investigated using high resolution infrared transient absorption spectroscopy at a series of ambient cell temperatures. The vibrationally hot (Evib≈5 eV) pyrazine molecules are formed by 248 nm excimer laser pumping, followed by rapid radiationless decay to the ground electronic state. The nascent rotational and translational product state distributions of the vibrationally excited CO2 molecules are probed at short times following the excitation of pyrazine. The temperature dependence of this process, along with the CO2 product state distributions, strongly suggest that the vibrational excitation of CO2 occurs via two mechanisms. The vibrational energy transfer is dominated by a long-range attractive force interaction, which is accompanied by almost no rotational and translational excitation. However, the CO2(0001) product state distribution also reveals a smaller contribution from a short-range interaction that results in vibrational excitation accompanied by substantial rotational and translational excitation. The long-range interaction dominates scattering into low angular momentum (J) states while the short-range interaction is most important for molecules scattering into high J states. The implications of these results for our understanding of the relaxation of molecules with chemically significant amounts of vibrational energy are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469142
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular supercollisions: Evidence for large energy transfer in the collisional relaxation of highly vibrationally excited pyrazine by CO2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6032-6045 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The temperature dependence of the collisional quenching of highly vibrationally excited pyrazine by CO2 molecules has been investigated for the temperature range 243–364 K using high resolution time resolved diode laser spectroscopy. Particular emphasis is placed on vibration to rotation-translation (V→R/T) energy transfer which leaves the CO2 vibrations unexcited and occurs predominantly through short-range repulsive forces. Vibrationally hot pyrazine is prepared by 248 nm excimer laser pumping, followed by rapid radiationless transitions to the ground electronic state. For the range of experimental cell temperatures used here, the nascent rotational population distributions of the 0000 ground state of CO2 resulting from collisions with hot pyrazine were probed at short times following excitation of pyrazine by the excimer laser pulse. The CO2 translational recoil velocity was also measured for individual rotational levels of the 0000 state. In addition, temperature dependent rate constants and probabilities were determined for energy transfer from the vibrationally hot pyrazine into individual rotational levels of the 0000 state of CO2. The rotational distributions, velocity recoils, and quenching rates exhibit a very weak temperature dependence for production of CO2 high J states, indicating that the CO2 molecules involved in these energy transfer events originate from rotational levels only slightly greater than the thermal mean J value. Based on these results, values for ΔE, the energy transfer from hot pyrazine to CO2 resulting in final CO2 0000 states J=58 through J=82, are estimated to range from 2550 to 7090 cm−1 in a single collision. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469338
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  • 5
    Electronic Resource
    Electronic Resource
    The collisional deactivation of highly vibrationally excited pyrazine by a bath of carbon dioxide: Excitation of the infrared inactive (1000), (0200), and (0220) bath vibrational modes (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2744-2755 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The collisional quenching of highly vibrationally excited pyrazine, C4H4N2, by CO2 has been investigated using high resolution infrared transient absorption spectroscopy at a series of cell temperatures. Attention is focused on collisions which result in excitation of the Fermi-mixed bath vibrational states (1000) and (0200), along with the unmixed overtone bend state (0220). The vibrationally hot (Evib(approximate)5 eV) pyrazine molecules are formed by 248 nm excimer laser pumping, followed by rapid radiationless decay to the ground electronic state. The nascent rotational and translational product state distributions of the CO2 molecules in each vibrationally excited state are probed at short times following the excitation of pyrazine. The temperature dependence of this process, along with the CO2 product state distributions and velocity recoils, strongly suggest that the vibrational excitation of CO2 is dominated by a long-range electrostatic interaction despite the fact that the dipole transition matrix elements connecting the CO2 ground state to the excited states vanish for the isolated molecule. The vibrational energy transfer is accompanied by very little rotational and translational excitation and displays the characteristic strong, inverse temperature dependence (probability of transfer increases with decreasing temperature) expected of energy transfer mediated by a long range attractive interaction. A number of possible explanations for this apparent anomaly are considered, of which energy transfer mediated by dipole/quadrupole forces appears to be the most consistent with the data. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475666
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  • 6
    Electronic Resource
    Electronic Resource
    Connecting quantum state resolved scattering data directly to chemical kinetics: Energy transfer distribution functions for the collisional relaxation of highly vibrationally excited molecules from state resolved probes of the bath (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3558-3566 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An energy transfer probability distribution function, P(E,E), for the collisional relaxation of a highly vibrationally excited donor molecule (C6F6, pyrazine) is constructed for the first time from experimental data on the bath (CO2) energy gain. A prescription for mapping bath quantum state resolved data onto P(E,E) is described in detail. Analysis of earlier experimental data allows a calculation of the high ΔE=E−E region (−7000 cm−1〈E−E〈−1500 cm−1) of P(E,E) for the above systems. Comparison of the P(E,E) functions reveals that C6F6 is a more efficient donor molecule than pyrazine, in agreement with previous experiments and trajectory calculations. In addition, resonance like structures in the P(E,E) functions arising from long range force mediated, V–V excitation of the carbon dioxide ν3 mode are discussed. These results indicate that accurate P(E,E) functions can be determined from experiments involving probes of the bath energy gain. This technique can be expected to provide stringent tests of current energy transfer theory and can, in principle, be used in conjunction with measurements of thermal kinetics to obtain energy dependent unimolecular rate constants, kE. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473452
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  • 7
    Electronic Resource
    Electronic Resource
    Translational and rotational excitation of the CO2(0000) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene: Evidence for impulsive collisions accompanied by large energy transfers (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7055-7071 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relaxation of highly vibrationally excited perfluorobenzene (C6F6) by collisions with CO2 molecules has been investigated over the temperature range 243–364 K using diode laser transient absorption spectroscopy. Particular focus is placed on understanding both the dynamical features and the kinetics of collisions which are accompanied by large energy transfers into the CO2 rotational and translational degrees of freedom. Vibrationally hot perfluorobenzene (Evib=41 822 cm−1) was prepared by 248 nm excimer laser pumping, followed by rapid radiationless transitions to the ground electronic state. The nascent rotational population distributions (J=64–80) of the 0000 ground state of CO2 resulting from collisions with hot perfluorobenzene were probed at short times following the excimer laser pulse. Doppler spectroscopy was used to measure the distributions of CO2 recoil velocities for individual rotational levels of the 0000 state. In addition, the temperature dependence of the state resolved, absolute rate constants for collisions populating high J states of CO2 was determined. The rotational distributions, distributions of recoil velocities, and quenching rates for production of CO2 high J states (J=64–80) exhibit a very weak temperature dependence. The slight temperature dependence indicates that CO2 molecules which scatter into high J states of the ground vibrationless level originate from rotational levels near the mean of the pre-collision thermal rotational distribution. A gap law model is used to estimate the probability of collisions which are accompanied by large energy transfers yielding values less than 2×10−5/cm−1 for ΔE〉2000 cm−1. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473675
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  • 8
    Electronic Resource
    Electronic Resource
    Scanning near-field infrared microscopy and spectroscopy with a broadband laser source (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4832-4839 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A scanning near-field microscope that allows the fast acquisition of midinfrared absorption spectra is described. The microscope couples the nanoscale spatial resolution of a scanning probe microscope with the chemical specificity of vibrational spectroscopy. Key design elements of the microscope include a tunable broadband infrared light source; an infrared focal plane array-based spectrometer which allows parallel detection of the entire pulse bandwidth (200 cm−1); and a single mode, fluoride glass, near-field probe fabricated with a chemical etching protocol. Infrared transmission images of a micropatterned thin gold film are presented that demonstrate spatial resolution conservatively estimated to be λ/7.5 at 3.4 μm, in the absence of optical artifacts due to topography. Constant height mode images of a polymer nanocomposite demonstrate instrumental sensitivity to fractional transmission changes of 1×10−3. Near-field absorption spectra (λ=3.4 μm) of a 2 μm thick polystyrene film are presented which demonstrate the instrumental sensitivity required for high spatial resolution, near-field absorption imaging. These spectra are acquired in 2 s and indicate a film thickness detection limit for polystyrene of 200 nm. Measurements exploring the coupling between the infrared absorption magnitude and changes in tip–sample separation suggest that near-field absorption imaging is relatively insensitive to topographic artifacts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1309034
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  • 9
    Electronic Resource
    Electronic Resource
    Midinfrared molecular gas lasers optically pumped by a continuously tunable infrared optical parametric oscillator (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2215-2217 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of midinfrared super radiant pulses emitted from molecular gases pumped by a narrow-band, continuously tunable infrared optical parametric oscillator. Molecules pumped either into a vibrational combination band or a vibrational overtone state decay by means of super radiant emission to a lower vibrationally excited state. Emission was observed in N2O at 4.5 and 8 μm, and in C2H2 at 13.6 μm and 15.7 μm. Pulse energies as high as 0.5 mJ and pulse widths as short as 7 ns make this an excellent technique for the production of intense midinfrared light. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118818
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  • 10
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    Midinfrared molecular gas lasers optically pumped by a continuously tunable infrared optical parametric oscillator (1997)
    American Institute of Physics
    Details
    Publication Date: 1997-04-28
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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