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  • 1
    Electronic Resource
    Electronic Resource
    Free radical chain reactions of chlorine with cyclobutane in the solid state: Evidence for radical migration via H atom transfer (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2847-2848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser-initiated reaction of chlorine with cyclobutane, deposited as a thin amorphous film at 77 K, is found to produce exclusively chlorocyclobutane and HC1 via a free radical chain mechanism. The reactions are initiated by pulsed laser photolysis of molecular chlorine at 308 nm. Product formation is monitored by Fourier transform infrared absorption spectroscopy. The quantum yield for reaction increases from 1.1±0.3 in an equimolar mixture to a yield of 7.4±0.8 for mixtures rich in cyclobutane. These results are consistent with a reaction mechanism which involves the transfer of a hydrogen atom from cyclobutane to cyclobutyl radical, permitting the radical site to propagate freely in the solid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454732
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  • 2
    Electronic Resource
    Electronic Resource
    Infrared fluorescence study of E–V energy transfer from Br*(4 2P1/2) to nitrosyl bromide (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2787-2792 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic-to-vibration (E–V) energy transfer from excited Br(4 2P1/2) atoms to nitrosyl bromide has been investigated by an infrared fluorescence technique. The excited bromine atoms are generated by pulsed laser photolysis of Br2 at 500 nm. Approximately 50% of the quenching collisions of Br*+BrNO yield BrNO molecules excited in the 1800 cm−1 v1 stretching mode. Of these, six times as many BrNO molecules are produced in the v1=1 state as in v1=2, despite the fact that the latter is nearly resonant with the electronic energy of Br*. The total rate coefficient for removal of Br* by BrNO is determined to be (1.5±0.2)×10−11 cm3 molecule−1 s−1. Indirect comparison of our results with previous work suggests that quenching proceeds primarily by inelastic collisions; reactive quenching to form Br2+NO is probably a minor channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452080
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  • 3
    Electronic Resource
    Electronic Resource
    Nitric oxide photofragment rotational distribution from UV dissociation of cyclopentadienylnickel nitrosyl (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7418-7423 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational state distribution for NO produced by dissociation of (η5–C5H5)NiNO near 225 nm has been obtained by [1+1] resonance-enhanced multiphoton ionization. The distribution is approximately characterized by a Boltzmann distribution at T=900±200 K. The relative populations of the two spin–orbit components of the ground 2Π manifold are also consistent with this temperature. No preference is observed for populating either of the lambda–doublet components, even at high rotational quantum numbers. Comparison of the results with statistical models shows that the state distribution is significantly colder than expected. One plausible explanation for this is that the parent molecule dissociates to produce cyclopentadienylnickel fragments in an excited electronic state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454305
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  • 4
    Electronic Resource
    Electronic Resource
    Laser multiphoton ionization and photoelectron spectroscopy of Co(CO)3NO and Fe(CO)5 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6186-6199 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser multiphoton dissociation-resonance-enhanced multiphoton ionization (MPD-REMPI) and time-of-flight photoelectron spectra (TOF-PES) of Co(CO)3NO and Fe(CO)5 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Co+ and Fe+. Transitions observed in the MPD-REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF-PES spectra. The multiphoton dissociation process produces metal atoms in a broad distribution of states, ranging in energies up to 33 000 cm−1 for Co, and 32 000 cm−1 for Fe. The most intense REMPI lines are associated with low-lying electronic states (〈8500 cm−1 for Fe and Co). By tuning the laser to appropriate wavelengths, neutral metal atoms in selected electronic states may be ionized. At most laser wavelengths, the atomic metal ions are formed in a distribution of states, only some of which are consistent with preservation of the core configuration of the Rydberg intermediate in the ionization step. An exception appears for ionization of Co atoms via 4d Rydberg intermediate states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458988
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  • 5
    Electronic Resource
    Electronic Resource
    Photofragment spectroscopy of cobalt tricarbonylnitrosyl and its trialkylphosphine derivatives (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1694-1700 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of gaseous Co(CO)3(NO) and Co(CO)2(NO)(PX3), where X=CH3, C2H5, n-C3H7, and n-C4H9 has been investigated near 225 nm by state-selective multiphoton ionization detection of nitric oxide fragments. The observed NO photofragment rotational distributions in v=0 are approximately Boltzmann, and the characteristic temperature decreases with increasing size of the phosphine ligand. The yield of photofragments appearing within the 10 ns detection time scale also decreases with increasing molecular size. An analogous effect is observed for the v=1/v=0 vibrational population ratio of the NO photoproducts. These results show that intramolecular energy transfer is fast compared with scission of the Co–NO bond. A dissociation model is proposed involving initial loss of CO followed by loss of other ligands via an RRKM-like process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456062
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  • 6
    Electronic Resource
    Electronic Resource
    A two-laser pulse-and-probe study of T-R, V energy transfer collisions of H+NO at 0.95 and 2.2 eV (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 660-667 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational, rotational, and spin-orbit state distributions are obtained for inelastic collisions of H+NO at 2.2 and 0.95 eV. The H atoms are generated by excimer laser photolysis of H2S at 193 and 248 nm, respectively, and the excited states of the NO molecules are probed by laser-induced fluorescence using a tunable dye laser. The rotational state distribution accompanying the T-V excitation of v=1–3 at 2.2 eV is approximately characterized by a Boltzmann distribution at 1275 K, and is essentially independent of the vibrational level excited. At 0.95 eV, the rotational populations are approximately characterized by a 1050 K distribution. In each case, the temperatures of the spin-orbit state populations and the rotational states are the same. No selective population of Λ-doublet states is observed. The results are discussed in terms of chemical interactions between these two open-shell species on the HNO potential energy surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449534
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  • 7
    Electronic Resource
    Electronic Resource
    Dipole broadened line shape of impurity chromophores isolated in a transparent matrix (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9563-9567 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The inhomogeneous broadening caused by dipole–dipole interactions between molecules having strongly allowed optical transitions is considered for the case in which the chromophores are randomly distributed at low concentration in a transparent matrix. Model calculations show that absorption in the wings of the spectrum is caused almost exclusively by strongly interacting pairs of chromophores. This result has important implications for the interpretation of recent experiments in which the spectra of single dye molecules have been observed in organic matrices. The generalized lineshape in these wings is shown to be proportional to the inverse square of the detuning from line center. The line shape is also somewhat asymmetric, with the red wing being more intense than the blue. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469970
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  • 8
    Electronic Resource
    Electronic Resource
    Dipole mechanism of line broadening in amorphous solids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 67-74 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dipole–dipole interaction between molecular vibrations is the most important source of inhomogeneous line broadening in the strongest infrared absorption bands of amorphous films of N2O and O3 prepared by vapor deposition at cryogenic temperatures. This type of broadening occurs in all strongly allowed absorption bands of amorphous solids. Comparison of spectra obtained for amorphous and polycrystalline ozone show that the crystal structure is anisotropic, and most likely uniaxial. The absorption line shape of amorphous films is satisfactorily predicted by a computational model in which orientationally disordered molecules on a regular lattice interact through long-range dipole interactions. It is shown that the normal vibrations are delocalized throughout the solid, and the absorption line shape depends on the macroscopic shape and orientation of the sample. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469445
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  • 9
    Electronic Resource
    Electronic Resource
    Photochemistry of ozone in solid mixtures with argon (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 292-298 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photochemistry of solid ozone and solid solutions of ozone in argon has been investigated at 10–30 K using 266 nm laser irradiation and detection by ultraviolet and infrared absorption spectroscopies. Pure ozone is converted to O2 with a quantum yield of 2.0±0.3 (independent of temperature) due to reaction of each photolytically generated O atom with a second ozone molecule. The quantum yield decreases when O3 is diluted in argon because geminate recombination of O+O2 becomes competitive with the O+O3 reaction. Photodissociation of ozone monomers is thought to occur by direct cage escape, which forms a separated O+O2 pair. This is the first experimental study in which the temperature dependence of the escape probability has been systematically investigated. The apparent activation energy of the process, 0.38±0.08 kJ/mol, is consistent with excitation of librations of ozone in the argon lattice, which brings it into orientations that are favorable for direct cage escape of the O atom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468182
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  • 10
    Electronic Resource
    Electronic Resource
    Infrared line shapes of clusters and microcrystals: Vibrational modes mixed by dipole interactions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 972-977 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mixing of near-degenerate vibrational modes by long-range dipole–dipole interactions can lead to complicated band shapes in the infrared spectra of clusters and microcrystals, particularly when the bands are inhomogeneously broadened as a result of distributions of crystal shapes and orientations in the sample. For the special case in which the clusters have isotropic crystal structures, the equivalence of amplitude vectors for all IR-active vibrational phonon modes permits the band shapes of dipole-mixed modes to be predicted from those of isolated modes. This analysis is successfully applied to experimental infrared spectra of thin films containing weakly interacting microcrystals of CO2 or N2O, as well as to CO2 clusters prepared by condensation in the gas phase. The results prove that these gas-phase clusters of CO2 have an isotropic crystalline structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466579
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