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  • Elsevier  (1,387)
  • American Institute of Physics (AIP)  (64)
  • Amsterdam : Elsevier
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  • 11
    Electronic Resource
    Electronic Resource
    Nonadiabatic electronic interactions in the ion-pair states of NeICl (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4171-4181 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonadiabatic interactions in the NeICl van der Waals complex have been explored in the lowest energy triad of ICl ion-pair states (∼39 000 cm−1). Dispersed fluorescence measurements reveal emission characteristic of multiple ion-pair electronic states, with the relative contributions from the E(0+), β(1), and D'(2) states changing with the initial ICl vibrational excitation (vICl). Emission directly from NeICl (vICl=0) complexes indicates that the initially prepared NeICl levels have mixed electronic character and that the ICl electronic parentage changes with the initial van der Waals vibrational level selected. NeICl complexes prepared with 1–4 quanta of ICl stretch undergo rapid vibrational predissociation with a strong propensity for ΔvICl=−1 relaxation. The electronic state(s) populated in the ICl fragments differ from the mixed electronic character of the initially prepared level, demonstrating that vibrational predissociation is accompanied by nonadiabatic electronic state changing processes. The observed final state selectivity may be attributed to the relative strength of the nonadiabatic couplings between the initial NeICl bound state and the final ICl states or a momentum gap rationale based on the overlap between the NeICl bound state wave function and the highly oscillatory continuum wave function of the separating fragments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460650
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  • 12
    Electronic Resource
    Electronic Resource
    Fragment energy and vector correlations in the overtone-pumped dissociation of HN3 X˜ 1A' (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 250-261 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: NH stretching overtone and combination states in HN3 X˜ 1A' were excited by IR–visible double resonance pumping and by direct overtone pumping in the range 6ν1 (17 670 cm−1) to 7ν1 (20 070 cm−1). NH fragments in the a 1Δ and X 3Σ− states were detected by laser induced fluorescence with sub-Doppler resolution to determine branching ratios, correlated fragment rotational state and kinetic energy distributions, and fragment vector correlations. The spin-forbidden triplet channel was accessible to all states excited, while the threshold for the singlet channel was determined to lie in the range 18 190 to 18 755 cm−1. The measured energy release places limits on the HN–NN bond energy, and the heights of barriers to reaction. The barrier in the singlet exit channel is at least 540 cm−1. The singlet channel accessed by 7ν1 dissociation is characterized by a Boltzmann-like NH rotational distribution (〈J NH〉≈3.5), highly excited N2 rotations (〈JN2〉 ≥ 20), and total translational energy release peaked away from zero (〈ET〉≈1350 cm−1). Vector correlations and Λ-doublet propensities indicate that nonplanar dissociation processes influence the NH rotations, but become less important for higher NH rotational states. The principal correlations are a strong positive recoil anisotropy (β≈0.6), a weak positive v–J correlation (βvJ≈0.17), and a JNH-dependent Λ-doublet propensity. A model using parent vibrational motion projected onto fragment rotation is suggested to explain these observations. The triplet channel exhibits similar NH and N2 rotational state distributions, with most of the available energy (substantially greater than in the singlet channel) appearing as fragment kinetic energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460392
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  • 13
    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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  • 14
    Electronic Resource
    Electronic Resource
    Population lifetimes of OH(v=1) and OD(v=1) stretching vibrations of alcohols and silanols in dilute solution (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5004-5018 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond infrared pump–probe experiments determined the vibrational population lifetimes (T1) of the hydroxyl fundamental stretching mode OH(v=1) in 12 alcohols (R3COH) and 8 silanols (R3SiOH) in dilute room temperature CCl4 solutions. T1 for the silanols is in the range 185〈T1〈292 ps, while T1 for the alcohols is much less (T1〈80 ps). The deuterium-exchanged analogs (COD and SiOD) exhibit population relaxation times similar to protonated hydroxyls. An analysis of the vibrational energy levels corresponding to modes involving the four bonds nearest the hydroxyl groups of these molecules is used to qualitatively explain the trends of the observed T1 lifetimes for these systems. Solution T1 lifetimes are also compared to those previously measured for OH(v=1) on the surface of silica and in other condensed-phase, room temperature systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451690
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  • 15
    Electronic Resource
    Electronic Resource
    Overtone-excited HN3(X˜ 1A'): Anharmonic resonance, homogeneous linewidths, and dissociation rates (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2782-2789 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution spectra have been obtained for the predissociative N–H stretching overtone levels 5ν1 (15 120 cm−1) and 6ν1 (17 670 cm−1) of HN3, cooled in a free-jet expansion. The spectral bandwidth (Doppler limited at 0.007 cm−1 full width at half-maximum (FWHM) is sufficiently narrow to reveal the homogeneous linewidths of individual rovibrational transitions in the 6ν1 band, for which we previously measured the dissociation lifetime in time-domain experiments. Two distinct manifestations of vibrational coupling characterize the spectra: (a) anharmonic mixing of the N–H stretch with other vibrational motions to give a complex spectrum of vibrational eigenstates and (b) homogeneous widths of the resultant states determined by the dissociation lifetime. The results are discussed with reference to previous studies of overtone spectroscopy and intramolecular mixing. Time-domain measurements of dissociation rates are reported for four vibrational levels with zero-order labels 5ν1 +νx. Over the range 15 100 cm−1–17 700 cm−1, the dissociation rate increases monotonically with vibrational energy, with no apparent "mode-specific'' variations. This is interpreted in terms of the highly mixed character of any particular vibrational eigenstate that is excited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457924
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  • 16
    Electronic Resource
    Electronic Resource
    Time resolved studies of vibrational relaxation dynamics of CO(v=1) on metal particle surfaces (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4619-4620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation dynamics of CO chemisorbed on small Pt and Rh particles supported on SiO2 has been investigated by picosecond time-resolved infrared transient bleaching experiments. A vibrational T1 lifetime of ≈7 ps has been observed for several different samples, independent of polarization, pump intensity, and sample temperature from 100–400 K. A 1:3 isotopic dilution has no effect upon T1. This T1 lifetime is a factor of 10–50 times shorter than T1 reported for metal carbonyl cluster compounds in solution and on SiO2 supports. Two possible mechanisms are considered to account for the rapid T1 decay; redistribution of the energy throughout the broad CO vibrational band, and relaxation directly to electron–hole pairs in the metal particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456598
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  • 17
    Electronic Resource
    Electronic Resource
    The spectroscopy and A state dynamics of the NeIBr van der Waals complex (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3171-3180 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A 3Π1←X 1Σ+ laser-induced fluorescence excitation spectrum of the NeIBr van der Waals complex is reported and analyzed to extract information regarding the structure and vibrational predissociation dynamics of the complex. While no definitive geometric information regarding NeIBr is obtained, our data indicate that a linear geometry is at least plausible. The vibrational predissociation lifetimes are a strong function of A state vibrational level and range from 2.6 to 23 ps. The variation in lifetime with vibrational level is consistent with the results of previous measurements on rare gas–halogen complexes, particularly NeBr2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455867
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  • 18
    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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  • 19
    Electronic Resource
    Electronic Resource
    Dissociation lifetimes and level mixing in overtone-excited HN3(X˜ 1A') (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7037-7045 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational overtone photodissociation is used to examine the spectroscopy and vibrational predissociation lifetimes of HN3 in its ground electronic state. Direct overtone pumping of the N–H stretching levels 5νNH and 6νNH prepares molecules in selected states (v,J,K) near 15 100 and 17 700 cm−1 of vibrational energy; spin-forbidden NH(X 3 Σ−) dissociation fragments are detected by laser-induced fluorescence. Photodissociation spectra of beam-cooled HN3 display mixing of individual rotational levels of the nνNH vibrations with several background states, with derived coupling matrix elements in the range 0.01–0.1 cm−1. Vibrational predissociation lifetimes of mixed components of 5νNH are state specific, with variations of a factor of 2 for only 0.1 cm−1 energy differences. Average lifetimes for low J, K are 210 ns for 5νNH and 0.95 ns for 6νNH. The ratio of decay rates for the two overtone levels, k(6νNH)/k(5νNH)=220, is much greater than predicted by statistical theory, which gives a ratio of 4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456230
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  • 20
    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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