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  • 1
    Electronic Resource
    Electronic Resource
    Unimolecular dynamics following vibrational overtone excitation of HN3 v1=5 and v1=6: HN3(X˜;v,J,K)→HN(X 3Σ−;v,J,Ω)+N2 (X 1Σ+g) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 608-609 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excitation of the NH-stretch overtone transitions of HN3 to v1=5 and 6 resulted in predissociation to HN(X) and N2(X) with lifetimes of 80+60−30 and ≤3 ns, respectively. Following excitation of either overtone, the HN fragments were formed predominantly in the symmetric F1, F3 spin–rotation states, with less than 4% population in the antisymmetric F2 levels. Fragment Doppler profiles confirmed that most of the available energy (〉96%) went into translational motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455454
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  • 2
    Electronic Resource
    Electronic Resource
    Picosecond study of the population lifetime of CO(v=1) chemisorbed on SiO2-supported rhodium particles (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5342-5343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared pump–probe characterization of the excited state lifetimes reveals that CO bound to isolated metal sites (T1=140±20 ps) persists longer than the signal observed for CO bound to (approximate)35 A(ring) diameter metal particles (≤18 ps), suggesting paticipation of electron–hole excitations in the larger metal particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455626
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  • 3
    Electronic Resource
    Electronic Resource
    CO(v=1) population lifetimes of metal–carbonyl cluster compounds in dilute CHCl3 solution (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 230-239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Tunable infrared picosecond pulses in the 5 μ region have been used for time-resolved pump–probe measurements of the population relaxation lifetime (T1) of CO(v=1) stretching vibrations in a series of metal–carbonyl cluster compounds in room temperature chloroform solution. T1 was the same for symmetric (ν=2084 cm−1, 90±10 ps) and antisymmetric (2014 cm−1, 87±10 ps) modes of the dicarbonyl Rh(CO)2(C5H7O2); T1 was the same for the B1 (2092 cm−1 , 710±130 ps) and B2 (2036 cm−1, 750±90 ps) modes of Rh2(CO)4Cl2. Similarly long T1 times were found for Rh4(CO)12 (2075 cm−1, 610±65 ps) and Rh6(CO)16 (2077 cm−1, 700±100 ps). The molecule Co4(CO)12 has also been compared to the corresponding rhodium analog and it exhibits an initially fast relaxation of 47±5 ps followed by a slower 396±70 ps decay. The transient response of the more complex systems to the single frequency experiment is found to be sensitive to frequency and can exhibit bleaching, absorption, and a combination of these effects. Such behavior is attributed to overlap of the IR pulse with v=1 to v=2 and higher transitions in the M4(CO)12 (M=Rh or Co) and Rh6(CO)16 molecules. The long CO(v=1) T1 values for the metal cluster molecules suggest relaxation via multiquantum transfer of vibrational energy to adjacent M–C stretch and M–C–O bend vibrations; energy transfer to vibrational or electronic states of the central metal core seems unimportant in determining T1 for these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455510
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  • 4
    Electronic Resource
    Electronic Resource
    Energetics and spin- and Λ-doublet selectivity in the infrared multiphoton dissociation DN3→DN(X 3Σ−, a 1Δ)+N2(X 1Σ+g): Experiment (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1378-1387 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiphoton vibrational excitation of deuterated hydrazoic acid, DN3, by a CO2 laser (I=10 GW/cm2) leads to dissociation forming DN in both X 3Σ− (spin forbidden) and a 1Δ (spin allowed) electronic states. Under collisionless conditions, the nascent DN fragments were probed via laser induced fluorescence, to determine initial product state distributions. The DN(X 3Σ−) molecules are formed predominantly in the symmetric F1 and F3 spin–rotation states with little population (≤6%) in the antisymmetric F2 levels. There is no significant population (〈3%) in excited DN(3Σ−) vibrational levels. The distribution of rotational states is Boltzmann-like, characterized by a rotational "temperature'' of about 920 K for the F1, F3 states and 500 K for F2 levels. Doppler profiles showed a large kinetic energy release of about 10 100 cm−1 total in the triplet channel. The DN(1Δ) products are formed preferentially in the symmetric Δ(A'), e-labeled lambda doublet levels: Δ(A')/Δ(A‘)=1.44. The DN(1Δ) is formed with no vibrational excitation (〈2%); the rotational states are populated Boltzmann-like with a rotational "temperature'' of 425 K. Doppler profiles give a total kinetic energy of about 1500 cm−1 in this channel. These observations give information about the distribution of energy in the reactant, the location of the barriers to dissociation, and the geometry of the transition states. Alexander, Werner, and Dagdigian (accompanying article) show that the observed DN(3Σ−) spin- and DN(1Δ) Λ-doublet selectivities reflect the symmetry properties of a planar transition state and that the low degree of DN(3Σ−) rotational and vibrational excitation is also expected from the transition state geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455137
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  • 5
    Electronic Resource
    Electronic Resource
    Time- and state-resolved measurements of nitric oxide dimer infrared photodissociation (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1966-1976 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond and nanosecond lasers and pulsed molecular beam techniques have been used to measure the infrared photodissociation spectra, the product state distributions, and the predissociation lifetimes of vibrationally excited nitric oxide dimer (NO)2 . Results for the ν1 (v=1) symmetric NO stretching mode and the ν4 (v=1) antisymmetric NO stretching mode are presented. Predissociation lifetimes are determined by time-resolved laser induced fluorescence probing of the NO monomer product appearance rate. A dramatic mode dependence of the predissociation lifetimes is observed with the higher energy ν1 mode decaying in approximately 1 ns, and the lower energy ν4 mode decaying in approximately 40 ps. The mode dependence is independent of which product state is probed. The product state distributions show that 75% to 80% of the available energy is channeled into relative translational energy of the fragments for both modes. Rotational state distributions are Boltzmann-like with temperatures ranging from 71 to 112 K depending on both the initially excited mode and on the NO product spin–orbit state. Predissociation from ν1 produces NO fragments in the 2Π1/2 and 2 Π3/2 states with equal probability. Predissociation from ν4 exhibits a propensity for producing the lower energy 2 Π1/2 spin–orbit state. The observations are discussed in terms of various vibrational predissociation mechanisms, including vibrational potential coupling and electronically nonadiabatic predissociation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455694
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  • 6
    Electronic Resource
    Electronic Resource
    Field-induced magnetic anisotropy in a dilute dispersion of γ Fe2O3 particles (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1691-1693 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The application of an alternating field (AF) of 60-mT peak to an isotropic sample containing dilutely dispersed particles of γFe2O3 from magnetic tape causes it to become magnetically anisotropic. The anisotropy of initial susceptibility so produced can be described by an oblate ellipsoid of revolution with the unique axis aligned with the AF direction. A consequence of this effect is that an isothermal remanent magnetization (IRM) is then more easily acquired if the direct field is applied perpendicular to the previously applied AF direction than if it is applied parallel to this direction. The anisotropy of IRM acquisition at direct fields between 20 and 40 mT is an order of magnitude greater than the anisotropy of initial susceptibility and is 40% of the maximum possible value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339903
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  • 7
    Electronic Resource
    Electronic Resource
    Separation of losses in low-alloy, nonoriented electrical steels (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4226-4228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recent study on low-alloy, nonoriented, semiprocessed electrical steels indicated that at 60 Hz and 15 and 17 kG the anomalous loss per cycle Wa increased linearly with t2/ρ, i.e., Wa=Wao+kt2/ρ, where t is sheet thickness, ρ is resistivity, and Wao and k are empirical constants. The present study explores the above relationship over inductions B of 5 to 17 kG and frequencies f of 20 to 200 Hz. A separation of hysteresis loss Wh into synchronous and asynchronous components is also considered. Six laboratory heats with Si+Al〈1.1 wt. % were hot and cold rolled to 0.035, 0.07, and 0.11 cm. The sheets were annealed, critically strained, and decarburized. Longitudinal strips were tested with dc as well as ac current in a 25-cm Epstein frame. The above linear equation was generally valid. At each combination of B and f, the intercepts Wao were always positive, but the slopes k were negative at 5 and 10 kG and positive at 15 and 17 kG. Furthermore, a fifth of the Wa values were negative. The negative Wa and k were associated with lack of flux penetration. Wh, but not Wa, increased with increasing oxygen and decreasing grain size, and these effects resided in the B1.6 component of Wh.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334621
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  • 8
    Electronic Resource
    Electronic Resource
    Energy distribution in the nitric oxide fragments from the ν7 vibrational predissociation of NO–C2H4 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5286-5288 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational level distribution of the NO fragments formed as a result of the predissociation of the vibrationally excited NO–C2H4 (ν7) van der Waals molecule was measured by laser excited fluorescence techniques. The distribution was found to be Boltzmann in character, described by the rotational temperature 75±15 K. An average kinetic energy release of ≈105 cm−1 per fragment, in an isotropic flux distribution, was determined from Doppler profiles of the NO fragments in selected rotational levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448604
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  • 9
    Electronic Resource
    Electronic Resource
    Infrared multiphoton dissociation of methyl nitrite in a molecular beam: Internal states of the nitric oxide fragment (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2236-2239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational-, spin-, and lambda doublet-state distributions for nitric oxide (NO) formed in the CO2 laser multiphoton dissociation of methyl nitrite, CH3ONO, in a pulsed molecular beam are reported. Upon methyl nitrite photolysis by temporal square wave infrared laser pulses at 983 cm−1 of 50 ns duration and 800 MW/cm2 intensity, the low-lying rotational levels of the nitric oxide fragments formed in the 2Π1/2 (F1) and 2Π3/2 (F2) spin-orbit states exhibited Boltzmann-like population distributions, characterizable by the rotational temperatures TR (F1)=400±10 K and TR (F2)=530±100 K; the integrated populations for J〈30.5 of the two spin components were in the ratio F1/F2=2.7 : 1. For those highly rotationally excited levels with J(approximately-greater-than)24.5 there is no measurable spin preference, the level population depending solely on total internal energy Eint. There is no apparent preference for formation of either lambda doublet component and there is no observable fragment alignment, the nascent NO species exhibiting an isotropic distribution of angular momentum vectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448317
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  • 10
    Electronic Resource
    Electronic Resource
    Vibrational deactivation of surface OH chemisorbed on SiO2: Solvent effects (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5216-5231 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond infrared transmission spectroscopy was used to directly measure the vibrational energy relaxation time T1 of hydroxyl groups chemisorbed on the surface of colloidal silica (SiO2). T1 was obtained for OH(νstretch=1) in the strongly bound "isolated sites'' of fumed silica particles in vacuum and dispersed in several liquids at T=293 K. At the SiO2/vacuum interface, T1=204±20 ps. When the SiO2 particles are surrounded by solvents, the relaxation time of the surface OH(v=1) groups decreases: for the liquids CCl4, CF2Br2, CH2Cl2, and C6H6, T1(ps)=159±16, 140±30, 102±20, and 87±30, respectively. T1 does not depend on the size of the SiO2 particles for the range 70 A(ring)≤ diameter ≤150 A(ring), or on the surface OH coverage up to an average density of 4 OH/100 A(ring)2. Significant amounts of physisorbed water (5 H2O/100 A(ring)2) decreased T1 for the isolated OH(v=1) to T1=56±10 ps. For comparison to the surface hydroxyls, the vibrational deactivation time for OH(v=1) groups in the bulk of fused silica (OH/SiO2≈130 ppm by weight) was determined to be T1=109±11 ps. These observations are discussed in terms of the possible mechanisms of vibrational energy flow in these systems. The observed T1 values demonstrate that the spectral linewidths (e.g., IR and Raman) observed for these surface vibrations are too large (by factors of 200–2000) to be caused solely by T1 uncertainty broadening. The slow transfer of vibrational energy between surface and lattice vibrations may have important implications for surface chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448646
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