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  • 1
    Electronic Resource
    Electronic Resource
    Gas-phase ion-molecule reactions of the nitric oxide anion (1989)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 111 (1989), S. 1203-1210 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00186a006
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  • 2
    Electronic Resource
    Electronic Resource
    Gas-phase reactions of negative ions with alkyl nitrites (1981)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 103 (1981), S. 7133-7140 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00414a016
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational autodetachment of NO− (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3136-3144 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report infrared cross sections for the photodetachment of the molecular anion NO− in the energy range of 1100–1500 cm−1. The measurements are made with a coaxial ion beam–laser beam aparatus. We observe a vibrational autodetachment resonance centered at 1284±10 cm−1. The resonance has a full width at half-maximum of 170 cm−1 corresponding to a lifetime of 0.35×10−12 s for NO−(v=1). The present value for the vibrational frequency of NO− is significantly lower than previous estimates obtained from photoelectron spectroscopy of NO− and from electron scattering resonances in NO. We discuss the implications of our results with regard to previous measurements of infrared photodetachment cross sections in the region 3000–4100 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455915
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  • 4
    Electronic Resource
    Electronic Resource
    On the exponential energy gap law in He–I2 vibrational relaxation (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2460-2468 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comparison between coupled states, infinite order sudden, and classical path calculations is used to elucidate the origin of an exponential energy gap law recently observed for vibrational relaxation from highly excited states in the B 0+u state of I2 due to collisions with He. All three methods provide relaxation cross sections in good agreement with experiment. Anharmonic effects play an important role, with accurate results obtained with a Morse, but not harmonic, oscillator description of the I@B|2 molecule. The nearly exact agreement between rotationally summed coupled states cross sections and the IOSA is consistent with the view that the I*2 molecule does not rotate significantly during a collision. A closed form solution of the forced harmonic oscillator, valid for highly excited states, predicts a J2||Δv|| distribution of vibrationally relaxed states at a given collision angle and impact parameter. The vibrationally close coupled-infinite order sudden (VCC-IOSA) results bear this out and show that the observed exponential scaling law arises from a superposition of such distributions over θ and b.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459026
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  • 5
    Electronic Resource
    Electronic Resource
    Convergence of the Magnus expansion for time dependent two level systems (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5647-5651 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper derives criteria for the convergence of the Magnus expansion, applied to an arbitrary time dependent two level system, in terms of the eigenvalues of the Hamiltonian for that system. When a weak to moderate intensity field perturbs a two level system the resonance frequency of the system must lie below the frequency of the applied field for the series to converge. An alternative solution for the exponential form of the evolution operator is developed that converges for all values of the expansion parameter and clearly shows the singularities that lead to the failure of the Magnus solution. Finally, a simple unitary transformation is presented that extends considerably the radius convergence of the Magnus series, as illustrated by a spin 1/2 in a linearly polarized field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452541
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  • 6
    Electronic Resource
    Electronic Resource
    Approximate algebraic solution to the forced highly excited rotor: Application to IB| 2 rotationally inelastic scattering (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6569-6583 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comparison between coupled states and classical path calculations is used to elucidate the power gap law for energy transfer observed in rotationally inelastic scattering of B 3Π0+uI2 by heavy atoms and the deviations from that law that occur for scattering by light mass species. An operator algebra is developed to describe raising and lowering of the eigenstates of j2 for highly excited rotational states. It forms the framework for a closed form solution of the forced rotor evolving under the Hamiltonian H=Ω/(h-dash-bar)⋅j2+V(θ,t). Transition probabilities are given by Bessel functions of the frequency component of the applied torque corresponding to the local rotational energy level spacing. This implies an oscillatory dependence of probability on ||Δj|| up to a ||Δj||max, beyond which it decreases dramatically. Integration of the oscillatory distribution in jf over impact parameter and degeneracy averaging yield the observed power law dependence of cross section on ||Δj|| along with the deviations from this law for light mass collision partners. The similarity of the present theory and results to previous work on vibrational relaxation of I*2 is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460284
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  • 7
    Electronic Resource
    Electronic Resource
    Application of a folding transformation to the Magnus solution for the evolution of periodically time dependent systems (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5167-5174 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two difficulties arise in the Magnus expansion for the evolution operator of a periodic time dependent Hamiltonian when the eigenvalues of the Hamiltonian are separated by more than 2π/τ, where τ is the period: (1) The Magnus expansion generally does not converge, and (2) the equilibrium properties of the system cannot be determined by statistical mechanical techniques analogous to those for time independent systems. A transformation is introduced that folds the eigenvalue spectrum into the interval −π/τ〈λi〈π/τ, yet retains the periodicity of the Hamiltonian, thereby alleviating the above difficulties. The method is compared to the approach taken by Shirley [Phys. Rev. B 138, 979 (1965)] for the Floquet solution to the evolution operator. It is applied to a dipole coupled spin system in an oscillating transverse field and the implications of the folding transformation on the spin thermodynamics of this system and the "Magnus paradox'' are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451710
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  • 8
    Electronic Resource
    Electronic Resource
    Ultraviolet spectroscopy of the B 2A' and C 2A‘ states of FCO (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8673-8680 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gas phase uv spectra of FCO obtained from the flash photolysis of F2, or F2CO, in the presence of CO are presented. The spectrum consists of three prominent progressions assigned to the B and C states of FCO and a fourth, weaker, progression which may belong to the second excited 2A' state. Analysis of the B 2A' state progressions provides vibrational frequencies of ω1=1180±35 cm−1 and ω2=770±30 cm−1 and a zero point energy in the range 24 000〈T0〈27 000 cm−1. The spectrum of the C 2A‘ state yields ω1=1458±6 cm−1 and ω2=651±5 cm−1 and a zero point energy of T0=28 500±25 cm−1. The electronic energies and vibrational frequencies are compared to recent ab initio calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466722
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  • 9
    Electronic Resource
    Electronic Resource
    The vibrational spectrum of FC(O)O radical: A challenging case for single-reference electron correlation methods (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6601-6607 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculation of the structure and vibrational spectrum of the fluoroformyloxyl radical, FC(O)O, using ab initio methods is complicated by orbital symmetry breaking in the Hartree–Fock wave function. While symmetry breaking is most directly corrected with multiconfiguration Hartree–Fock methods, the problem can also be attacked with single reference methods when combined with an electron correlation treatment that adequately mixes the Hartree–Fock determinants leading to the symmetry breaking. In this work the structure and vibrational spectrum of both the ground (X 2B2) and second excited (B 2A1) states of the FC(O)O radical are calculated using single-reference wave functions constructed in two different ways—unrestricted (UHF) and quasirestricted (QRHF) Hartree–Fock wave functions—in combination with a coupled cluster [CCSD and CCSD(T)] electron correlation treatment. We find that both methods must be employed with some caution, but in combination they provide reliable prediction of the vibrational spectrum of the FC(O)O radical. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470389
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  • 10
    Electronic Resource
    Electronic Resource
    A classical path/forced rotor theory of state-to-state rotational energy transfer (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5999-6012 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The problem of rotational energy transfer (RET) is examined from a point of view intermediate between the current approaches based on empirical models or numerical solution of the coupled scattering equations. A semiclassical perspective is taken in which a classically described collision with an atom exerts a time dependent torque on the rotor and the resulting forced rotor dynamics is addressed quantum mechanically. By treating the anharmonicity in the rotational energy levels as a perturbation, a simple approximate expression is found for the inelastic transition probability. It reveals a marked difference between the distribution of final rotational states incurred from an individual collision trajectory as compared to trajectory averaged measures of RET, such as cross sections. The theory is applied to the scattering of Li2(A 1Σ+u) by Ne, Ar, Xe;Na2(A 1Σ+u) by He and Ne; N+2(X 2Σ+g) by He, and CN(X 2Σ+) by He. Its predictions compare well with those from a fully quantum mechanical description of rigid rotor scattering and with experiment. The insight into the energy transfer dynamics gained from the semiclassical approach is used to examine the assumptions underlying empirical models of rotational energy transfer. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470428
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