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  • 1
    Electronic Resource
    Electronic Resource
    High-resolution near-infrared spectroscopy of water dimer (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6613-6631 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution near-infrared spectra are reported for all of the O–H stretch vibrational bands of the water dimer. The four O–H vibrations are characterized as essentially independent proton-donor or proton-acceptor motions. In addition to the rotational and vibrational information contained in these spectra, details are obtained concerning the internal tunneling dynamics in both the ground and excited vibrational states. These results show that for tunneling motions which involve the interchange of the proton donor and acceptor molecules, the associated frequencies decrease substantially due to vibrational excitation. The predissociation lifetimes for the various states of the dimer are determined from linewidth measurements. These results clearly show that the predissociation dynamics is strongly dependent on the tunneling states, as well as the Ka quantum number, indicating that the internal tunneling dynamics plays an important role in determining the dissociation rate in this complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457380
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  • 2
    Electronic Resource
    Electronic Resource
    A simple model for correcting the zero point energy problem in classical trajectory simulations of polyatomic molecules (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2863-2868 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple model is proposed for correcting problems with zero point energy in classical trajectory simulations of dynamical processes in polyatomic molecules. The "problems'' referred to are that classical mechanics allows the vibrational energy in a mode to decrease below its quantum zero point value, and since the total energy is conserved classically this can allow too much energy to pool in other modes. The proposed model introduces hard sphere-like terms in action–angle variables that prevent the vibrational energy in any mode from falling below its zero point value. The algorithm which results is quite simple in terms of the cartesian normal modes of the system: if the energy in a mode k, say, decreases below its zero point value at time t, then at this time the momentum Pk for that mode has its sign changed, and the trajectory continues. This is essentially a time reversal for mode k (only!), and it conserves the total energy of the system. One can think of the model as supplying impulsive "quantum kicks'' to a mode whose energy attempts to fall below its zero point value, a kind of "Planck demon'' analogous to a Brownian-like random force. The model is illustrated by application to a model of CH overtone relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456956
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  • 3
    Electronic Resource
    Electronic Resource
    Multiphoton ionization of vibrationally hot nitric oxide produced in a pulsed supersonic glow discharge (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2900-2908 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass-resolved, resonant multiphoton ionization (MPI) spectroscopy has been used to identify and characterize transient species produced in a pulsed, supersonic glow discharge source. Vibrationally hot (up to v‘=9), but rotationally cold nitric oxide is characterized by (1+1) MPI via the A 2Σ+ state and (2+1) MPI through the C 2Πr state. Nine A←X and six C←X hot bands are observed; only four of these have been previously characterized. Accidentally overlapping C and A state hot bands can be separately studied by using different order MPI schemes. Implications for several previous studies are discussed. Additionally, the 3P0,2 metastable rare gas atoms are readily formed and detected by MPI as are metal atoms sputtered from the electrodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455941
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  • 4
    Electronic Resource
    Electronic Resource
    The argon hydrogen–fluoride differential scattering cross section (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2182-2191 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The total differential cross section for Ar–HF was measured at a collision energy of 1637 K (141 meV). Although diffraction oscillations were not resolved, a broad primary rainbow peak was observed. Scattering calculations were carried out for the Ar–HF interaction potentials developed by Douketis et al. and Hutson and Howard. The spherical potential and infinite order sudden approximations do not give a good description of the total differential scattering. The final-l labeled coupled states approximation, on the other hand, is in good agreement with the more accurate close coupled approximation. Neither potential predicts cross sections which are in good agreement with the measured scattering intensities. Contributions to the total scattering from elastic and inelastic processes were investigated using the coupled states approximation. The contributions to the total scattering from different initial HF rotational states were also studied. The total scattering for j initial=0 differs significantly from that for other values of j initial. It is therefore important to know the distribution of rotational states in the HF beam if one is to compare calculated total differential cross sections with measured ones. The largest inelastic cross section is for the j=0 to j'=1 transition. Collisions in which the Ar atom interacts strongly with the anisotropic potential well, rather than near head-on collisions off the repulsive wall of the potential, are responsible for the large j=0 to j'=1 cross section. The results of accurate SCF calculations for Ar–HF are also reported in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456013
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  • 5
    Electronic Resource
    Electronic Resource
    Mode specific vibrational relaxation in the acetylene–hydrogen fluoride binary complex (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1478-1483 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optothermal molecular beam technique has been used to record the near infrared spectrum of the acetylene–HF binary complex associated with the ν7 vibrational mode (asymmetric C–H stretch). A fit to this perpendicular band spectrum gives accurate rotational constants for both the ground and excited vibrational states, as well as the vibrational origin, namely A‘=1.192 60(5) cm−1 , B‘=0.157 34(1) cm−1 , C‘=0.138 10(1) cm−1 , A'=1.186 90(5) cm−1 , B'=0.157 34(1) cm−1 , C'=0.138 08(1) cm−1, and ν0 =3276.2889(30) cm−1 . From the homogeneous linewidths of the observed transitions the lifetime of the excited vibrational state has been determined to be 3.6 ns. When compared with the lifetime determined previously for the ν1 mode (0.8 ns) and the data obtained previously for several other systems, it is clear that vibrational relaxation in this molecule is mode specific. A discussion is given concerning the nature of this relaxation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456090
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  • 6
    Electronic Resource
    Electronic Resource
    Picosecond dynamics of surface electron transfer processes: Surface restricted transient grating studies of the n-TiO2/H2O interface (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1253-1269 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The surface restricted transient grating is demonstrated as a sensitive probe of ultrafast surface reaction dynamics. Studies of doped single crystal n-TiO2 (001) surfaces in air demonstrate linear trapping processes, assigned to crystal defects within the surface deformation layer, that limit carrier lifetimes to 5 ns. Direct in situ grating studies at photochemically active n-TiO2/H2O interfaces demonstrate that the dominant mechanism of interfacial electron transfer in this system involves thermalized hole carriers at the atomic surface. The dynamics are consistent with adsorbed OH− as the initial hole acceptor. In addition, optical generation of coherent surface acoustic modes is demonstrated. A detailed theory is presented for the grating excitation of the surface acoustics. Acoustic propagation in the H2O half-space of the TiO2/H2O liquid interface gives evidence for a phase change of the water layer at the polar TiO2 (001) surface to a solid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456130
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  • 7
    Electronic Resource
    Electronic Resource
    Multiphoton ionization studies of NO: Spontaneous decay channels in the (4pπ)K 2Π(v=2) Rydberg state (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 754-761 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-delayed optical double resonance multiphoton ionization (MPI) studies involving (4pπ)K 2Π(v=2)←(3sσ)A 2Σ+(v=1) ←←X 2Π(v=0) NO show dramatic loss of the ionization signal amplitudes on a time scale that is very short relative to the lifetime of the A state. From direct comparisons of MPI and laser induced fluorescence (LIF) dip temporal profiles, it is concluded that loss of the signal amplitude results from inefficient ionization of the K state. MPI temporal profiles measured in a supersonic jet are identical with those measured in a cell indicating that collisional effects are not important. For delay times τ≥20 ns, ionization signals can be observed only at high probe laser intensities. The resultant spectra exhibit marked power broadening and a pronounced dip appears in the center of each of the power broadened resonances. The observed line shapes are rationalized in terms of the spatial and temporal distributions of the probe laser field in conjunction with a dynamical competition between photoionization and spontaneous decay channels in the K state. Such arguments lead to an upper bound on the K 2Π(v=2) lifetime of ≈2 ns. The short lifetime of K 2Π(v=2) is attributed to indirect heterogeneous predissociation through the (4pσ)M 2Σ+ state and/or to homogeneous predissociation via the a 4Π continuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456099
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational analysis of A˜ 2A1↔X˜ 2E electronic transition of the jet-cooled methylthio radical (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6852-6857 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A set of molecular parameters describing both the X˜ and A˜ states of CH3S, has been obtained by a joint fitting of the rotationally resolved electronic transitions observed in a free-jet-cooled laser-induced fluorescence study of CH3S and an earlier microwave study of its X˜ state. The present work shows that because of incomplete information, nearly all of the previously reported molecular parameters for CH3S must be significantly revised. The present observations show an unusual electronic structure for the radical, characterized by a short C–S bond distance and peculiar methyl group geometry in the ground state. The C–S bond is observed to lengthen markedly in the excited A˜ state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456258
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  • 9
    Electronic Resource
    Electronic Resource
    Picosecond multiphoton ionization of molecular clusters (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5203-5205 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High peak-power picosecond laser pulses have been used for the first time to effect nonresonant or resonant multiphoton ionization (MPI) of clusters generated in a supersonic nozzle expansion. The resultant ions are subsequently detected and characterized by time-of-flight mass spectroscopy. Specifically, we present preliminary results involving MPI of the cluster series (NO)n (n=1–4), and ArnI2 (n=1–10). Previous MPI studies of these two species using nanosecond lasers have not been successful, presumably due to fast dissociation channels. It is proposed that the present technique is a new and rather general ionization source for cluster studies which is complementary to electron impact but may, in addition, provide unique spectroscopic or dynamical information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456538
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  • 10
    Electronic Resource
    Electronic Resource
    The A 2Σ+ state of rare gas–NO van der Waals molecules probed by 1+1 multiphoton ionization spectroscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4031-4036 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The previously unobserved bound–bound spectra of ArNO, KrNO, and XeNO have been observed slightly blue shifted from the (1,0) and (0,0) bands of the A 2Σ+←X 2Π1/2 transition of uncomplexed nitric oxide. Although the structured but incomplete spectra cannot be assigned with certainty, limits to the ground and excited state bond dissociation energies, D‘0 and D0, respectively, can be estimated. For ArNO these limits are D‘0 ≥89 and 54 cm−1≤D0 ≤101 cm−1. The observed fragmentation of the KrNO and XeNO molecules, coupled with earlier results for MPI via the C 2Π state, suggests that superexcited, autoionizing states of the van der Waals molecules dissociate to yield excited rare gas atoms whenever energetically possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455813
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