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  • 1
    Electronic Resource
    Electronic Resource
    Normal mode and isomerization bending states in HCP: Periodic orbit assignment and spectroscopic signature (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 10055-10058 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present exact quantum mechanical bound-state calculations for HCP using an ab initio potential energy surface. The main result is the existence of two distinct families of bending states: one with normal-mode-type behavior and wave functions confined to small bending angles and the other one sampling the isomerization path all the way from H–CP to CP–H. Stable periodic orbits provide a clear-cut assignment. Possible relations to recent spectroscopic observations are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471729
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  • 2
    Electronic Resource
    Electronic Resource
    The unimolecular dissociation of HCO: I. Oscillations of pure CO stretching resonance widths (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3593-3611 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unimolecular dissociation of the formyl radical HCO in the electronic ground state is investigated using a completely new ab initio potential energy surface. The dynamics calculations are performed in the time-independent picture by employing a variant of the log-derivative Kohn variational principle. The full resonance spectrum up to energies more than 2 eV above the vibrational ground state is explored. The three fundamental frequencies (in cm−1) for the H–CO and CO stretches, and the bending mode are 2446 (2435), 1844 (1868), and 1081 (1087), where the numbers in parentheses are the measured values of Sappey and Crosley obtained from dispersed fluorescence excitation spectra [J. Chem. Phys. 93, 7601 (1990)]. In the present work we primarily emphasize the dissociation of the pure CO stretching resonances (0v20) and their decay mechanisms. The excitation energies, dissociation rates, and final vibrational–rotational state distributions of CO agree well with recent experimental data obtained from stimulated emission pumping. Similarities with and differences from previous time-independent and time-dependent calculations employing the widely used Bowman–Bittman–Harding potential energy surface are also discussed. Most intriguing are the pronounced oscillations of the dissociation rates for vibrational states v2≥7 which are discussed in the framework of internal vibrational energy redistribution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468588
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical study of the unimolecular dissociation HO2→H+O2. II. Calculation of resonant states, dissociation rates, and O2 product state distributions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8357-8381 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three-dimensional quantum mechanical calculations have been carried out, using a modification of the log-derivative version of Kohn's variational principle, to study the dissociation of HO2 into H and O2. In a previous paper, over 360 bound states were found for each parity, and these are shown to extend into the continuum, forming many resonant states. Analysis of the bound states close to the dissociation threshold have revealed that HO2 is a mainly irregular system and in this paper it is demonstrated how this irregularity persists in the continuum. At low energies above the threshold, these resonances are isolated and have widths that fluctuate strongly over more than two orders of magnitude. At higher energies, the resonances begin to overlap, while the fluctuations in the widths decrease. The fluctuations in the lifetimes and the intensities in an absorption-type spectrum are compared to the predictions of random matrix theory, and are found to be in fair agreement. The Rampsberger–Rice–Kassel–Marcus (RRKM) rates, calculated using variational transition state theory, compare well to the average of the quantum mechanical rates. The vibrational/rotational state distributions of O2 show strong fluctuations in the same way as the dissociation rates. However, their averages do not agree well with the predictions of statistical models, neither phase space theory (PST) nor the statistical adiabatic channel model (SACM), as these are dependent on the dynamical features of the exit channel. The results of classical trajectory calculations agree well on average with those of the quantum calculations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471587
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical study of the unimolecular dissociation HO2→H+O2. I. Calculation of the bound states of HO2 up to the dissociation threshold and their statistical analysis (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9947-9962 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This is the first of a series of papers in which we investigate the unimolecular dissociation of hydroperoxyl. Using the DMBE IV potential energy surface [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)], in the present study 726 bound states of HO2(X˜) up to the H+O2 dissociation threshold are calculated in an attempt to access the extent of the coupling between the modes of the system. The first approach involves an analysis of the nodal structure of the wave functions. While the wave functions for the lowest states are regular and assignable, the degree of mixing and complexity rapidly increases with energy. The wave functions close to the dissociation threshold are mostly irregular without any clear cut nodal structure and fill the entire coordinate space available. Nevertheless, a small number of regular states, that are associated with large excitation in the O2 stretching coordinate and no or only little excitation in the other modes, are found even at high energies. The second approach used to study the degree of intramolecular coupling is an analysis of the energy spectrum. The nearest neighbor level spacing distribution, which probes the short-range correlation, as well as the Σ2 and Δ3 statistics, which are sensitive to the long-range correlations in the spectrum, are investigated and compared to the distributions predicted for regular and irregular spectra. Both of these approaches indicate that the system is almost totally irregular with a Brody parameter of about 92%. In addition, the sum of states at a particular energy, which is extremely important in all statistical models for unimolecular dissociation, is approximately calculated from the volume of classical phase space and found to be in excellent agreement with the exact quantum mechanical result. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469884
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum mechanical study of the unimolecular dissociation of HO2: A rigorous test of RRKM theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5867-5870 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three-dimensional quantum mechanical calculations are carried out, in a time-independent scattering approach, to study the unimolecular dissociation HO2→H+O2. The dissociation cross section is governed by narrow resonances with widths that vary over five orders of magnitude. The unimolecular dissociation rates strongly fluctuate about an average which agrees surprisingly well with the Rampsberger–Rice–Kassel–Marcus (RRKM) theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469320
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  • 6
    Electronic Resource
    Electronic Resource
    Vibration–rotation excitation of CO by hot hydrogen atoms: Comparison of two potential energy surfaces (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5416-5422 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collision cross sections for rotational and vibrational excitation of CO by fast H atoms are calculated for two potential energy surfaces, the older Bowman–Bitman–Harding potential and the recently constructed surface of Werner, Keller, and Schinke. Both quantum mechanical and classical calculations are performed. The results obtained with the new potential energy surface are very similar to those obtained with the older potential; in particular, they do not rectify the discrepancies between the experimental and theoretical cross sections for vibrationally elastic transitions into small rotational states of CO. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472382
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  • 7
    Electronic Resource
    Electronic Resource
    The unimolecular dissociation of HCO. II. Comparison of calculated resonance energies and widths with high-resolution spectroscopic data (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4983-5004 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the unimolecular dissociation resonances of HCO in the electronic ground state, X˜1A′, using a new ab initio potential energy surface and a modification of the log-derivative version of the Kohn variational principle for the dynamics calculations. Altogether we have analyzed about 120 resonances up to an energy of ≈2 eV above the H+CO threshold, corresponding to the eleventh overtone in the CO stretching mode (v2=11). The agreement of the resonance energies and widths with recent stimulated emission pumping measurements of Tobiason et al. [J. Chem. Phys. 103, 1448 (1995)] is pleasing. The root-mean-square deviation from the experimental energies is only 17 cm−1 over a range of about 20 000 cm−1 and all trends of the resonance widths observed in the experiment are satisfactorily reproduced by the calculations. The assignment of the states is discussed in terms of the resonance wave functions. In addition, we compare the quantum mechanical state-resolved dissociation rates with the results of classical trajectory calculations and with the predictions of the statistical model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472347
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  • 8
    Electronic Resource
    Electronic Resource
    Highly excited vibrational states of HCP and their analysis in terms of periodic orbits: The genesis of saddle-node states and their spectroscopic signature (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 9818-9834 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present quantum mechanical bound-state calculations for HCP(X˜) using an ab initio potential energy surface. The wave functions of the first 700 states, corresponding to energies roughly 23 000 cm−1 above the ground vibrational state, are visually inspected and it is found that the majority can be uniquely assigned by three quantum numbers. The energy spectrum is governed, from the lowest excited states up to very high states, by a pronounced Fermi resonance between the CP stretching and the HCP bending mode leading to a clear polyad structure. At an energy of about 15 000 cm−1 above the origin, the states at the lower end of the polyads rather suddenly change their bending character. While all states below this critical energy avoid the isomerization pathway, the states with the new behaviour develop nodes along the minimum energy path and show large-amplitude motion with H swinging from the C- to the P-end of the diatomic entity. How this structural change can be understood in terms of periodic classical orbits and saddle-node bifurcations and how this transition evolves with increasing energy is the focal point of this article. The two different types of bending motion are clearly reflected by the rotational constants. The relationship of our results with recent spectroscopic experiments is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474226
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  • 9
    Electronic Resource
    Electronic Resource
    Unimolecular dissociation dynamics of highly vibrationally excited DCO(X˜ 2A). II. Calculation of resonance energies and widths and comparison with high-resolution spectroscopic data (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5359-5378 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the unimolecular dissociation of DCO in the electronic ground state, X˜ 1A, using a new ab initio potential energy surface. Altogether we have analyzed about 140 resonances up to an energy of (approximate)1.4 eV above the D+CO threshold, corresponding to the ninth overtone in the CO stretching mode (v2=9). The agreement of the resonance positions and widths with recent stimulated emission pumping measurements of Stöck et al. [J. Chem. Phys. 106, 5333 (1997), the preceding article] is pleasing. The root-mean-square deviation from the experimental energies is only 16 cm−1 over a range of about 16 500 cm−1 and all trends of the resonance widths observed in the experiment are satisfactorily reproduced by the calculations. A strong 1:1:2 stretch–stretch–bend resonance prohibits a unique assignment for the majority of vibrational states. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473599
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  • 10
    Electronic Resource
    Electronic Resource
    The unimolecular dissociation of HCO. IV. Variational calculation of Siegert states (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9887-9897 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new variational method for calculating complex resonance (Siegert) states in unimolecular dissociation reactions. The approach is based on the log-derivative version of the Kohn variational principle. The basic matrix equations can be formulated in terms of scattering-wave boundary conditions yielding the resonance states as homogeneous solutions for singular energies. Thus, the resonance positions and widths can be calculated directly without employing an artificial absorbing potential. This method is applied to the photodissociation of HCO and DCO and the results are compared to the resonance parameters obtained from absorption-type spectra. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478862
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