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  • 1
    Electronic Resource
    Electronic Resource
    High-resolution infrared spectroscopy of weakly bound molecular complexes (1988)
    s.l. : American Chemical Society
    Chemical reviews 88 (1988), S. 843-870 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr00088a003
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  • 2
    Electronic Resource
    Electronic Resource
    Multiple intermolecular bend vibrational excitation of a hydrogen bond: An extended infrared study of OCOHF (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7716-7730 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the use of near infrared tunable difference frequency laser absorption methods to investigate low-frequency bending of the intermolecular hydrogen bond in OCOHF complexes. By deliberate thermal warming of the slit jet expansion to 16 K, we observe bending "hot band'' transitions built on the fundamental vHF=1←0 HF stretch from the lowest five internally excited bending states (i.e., vlbend=00←00, 11←11, 20←20, 22←22, and 31←31) which correspond to low-frequency, skeletal bending of the intermolecular hydrogen bond. In addition, much weaker parallel (Δl=0) combination band transitions (vlbend=20←00 and 31←11 ) are observed at (approximately-less-than)5% of the 00←00 intensity. Furthermore, measurements of the extremely weak 11←00 perpendicular (Δl=1) band are obtained at (approximately-less-than)1% of the 00←00 intensity. The fundamental, hot band, and combination band data permit quantitative measurement of the absolute vibrational energies of all vibrational levels for the l=0 and 1 manifolds in both HF excited (vHF=1) and ground-state (vHF=0) complexes.The bending frequencies are surprisingly low (∼10 cm−1 ) and exhibit positive anharmonicity (i.e., the energy level spacings increase with vlbend ). The results suggest nearly unrestricted bending of the hydrogen bond in a very flat, highly anharmonic angular potential. In contrast with many other weakly bound complexes, the lowest bending frequency decreases dramatically upon HF excitation, which signals a vHF vibrationally induced shift from a linear to a nonlinear equilibrium geometry for the vHF=1 excited OCOHF potential surface. Excess Lorentzian line widths are observed in all OCOHF transitions, attributable to vibrational predissociation lifetimes that vary smoothly from 1.2 ns (vlbend=00) to 650 ps (vlbend=31) as a function of intermolecular bending excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459351
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  • 3
    Electronic Resource
    Electronic Resource
    Intramolecular dynamics of van der Waals molecules: An extended infrared study of ArHF (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2790-2807 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The near-infrared spectrum of ArHF prepared in a slit supersonic expansion is recorded with a difference frequency infrared laser spectrometer. By virtue of the high sensitivity of the technique, and the lack of appreciable spectral congestion at the 10 K jet temperature, we observe 9 of the 11 vibrational states with energies below the Ar+HF(v=1, j=0) dissociation limit. These include (1000), the lowest bound HF (v=1) state, the singly, doubly, and quadruply van der Waals stretch excited states (1001) (1002), and (1004), both the Σ bend (1200) and Π bend (111e,f 0), and the multiply excited, Π bend plus van der Waals stretch (111e,f 1). Two Ar+HF(v=0) states, (0000) and (0001), are also characterized. This spectroscopic information is quite sensitive to the Ar+HF potential energy surface away from the equilibrium configuration, and thus provides a rigorous test of trial potential energy surfaces. Excellent agreement is obtained between experiment and the predictions of a recently reported Ar+HF(v=1) potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456948
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of CH2 a˜ 1A1 (1,0,0) and (0,0,1) Coriolis-coupled states, a˜ 1A1–X˜ 3B1 spin–orbit coupling, and the equilibrium structure of CH2 a˜ 1A1 state (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6566-6578 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The symmetric and antisymmetric stretch spectra of a˜ 1A1 CH2 are measured with Doppler-limited resolution by infrared flash-kinetic spectroscopy between 2600 and 3050 cm−1. The spectra are significantly perturbed by spin–orbit interactions between near-resonant levels of X˜ 3B1 in both lower and upper levels of the transitions, and by Coriolis interaction between symmetric and antisymmetric stretch states. The triplet character of the perturbed levels is detected by observing broadening of MJ structure in a magnetic field of about 1 kG. The levels that are likely to be perturbed by triplet methylene are identified using the experimentally observed and theoretically calculated 3B1 energy level structure. The term values of the remaining symmetric and antisymmetric stretch levels are simultaneously fit to Watson's Hamiltonian including Coriolis coupling. This analysis provides the remaining information needed to determine the equilibrium rotational constants [Ae =19.8054(206), Be=11.2489(45), and Ce =7.2386(36) cm−1 ], and, therefore, the equilibrium structure (re=1.107 A(ring), and θe =102.4°) of this fundamentally important carbene. The experimental and theoretical structures are in good agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457375
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  • 5
    Electronic Resource
    Electronic Resource
    High-resolution, slit jet infrared spectroscopy of hydrocarbons: Quantum state specific mode mixing in CH stretch-excited propyne (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 104-113 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A direct absorption, difference frequency, infrared laser spectrometer with 10−4 cm−1 resolution combined with slit supersonic jet optical pathlengths is presented as a tool for the study of mode–mode vibrational coupling in laser-excited hydrocarbons. These weak mode–mode couplings are evidenced in our frequency domain studies by virtue of transitions to isolated upper J states that are split into multiplets under sub-Doppler resolution. Instrument performance is demonstrated by investigating vibrational coupling in the 3000–3300 cm−1 C–H stretch fundamental region of 12C3 propyne, as well as the 12C213C propynes observed in natural isotopic abundance. No appreciable state mixing is observed in ν1=1←0 and ν6=1←0 spectra at T=4 K. However, near-resonant two-state mixing of ν2 and ν5+ν8+3ν10 in the ν2=1←0 transition of 12C3 propyne is detected and deperturbed to provide an anharmonic coupling matrix element of 0.096 41(38) cm−1. This matrix element is independent of J' and thus arises from purely anharmonic, non-Coriolis-mediated couplings. The implications of anharmonic coupling matrix elements of this magnitude in overtone vibrational dynamics are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457496
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  • 6
    Electronic Resource
    Electronic Resource
    Rydberg–Klein–Rees inversion of high resolution van der Waals infrared spectra: An intermolecular potential energy surface for Ar+HF (v=1) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4855-4864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method is described for extraction of two-dimensional (angular and radial) potential energy surfaces for triatomic rare gas–hydrogen halide van der Waals complexes. The approach relies on extensive J rotational term values obtained by high resolution infrared laser jet spectroscopy for a family of bending vibrational states to deduce the radial and angular dependence of the intermolecular potential. First, effective 1D radial potentials for a series of bending states are obtained by rotational RKR analysis of experimentally observed rotational progressions. These 1D potentials, which represent vibrational averages over different bending wave functions, are then inverted to determine the radially dependent coefficients of a Legendre expansion to the full surface, i.e., ∑lVl(R)Pl (cos θ). This relies on adiabatic angular motion with respect to radial degrees of freedom, the validity of which is discussed. This approach is tested with experimental data from the (100 0) (fundamental), (120 0) (HF parallel bend), and (111 0) (HF perpendicular bend) of Ar+HF (v=1), excited up to J≤25. The accuracy of the resulting surface is verified by exact quantum bound state calculations which quantitatively reproduce the rovibrational input data, as well as predict the spectroscopic properties of five other vibrational states observed in the Ar+HF (v=1) system but not used in the fitting procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456579
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  • 7
    Electronic Resource
    Electronic Resource
    The dipole moment function and vibrational transition intensities of OH (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5455-5465 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative intensities of nine pairs of rovibrational transitions of OH in the v=1←0 fundamental have been measured by flash kinetic infrared absorption spectroscopy. Each pair of transitions originates from a common rotational and spin–orbit state, so that relative intensities are independent of the OH number density and quantum state distribution. The relative intensities are strongly J dependent and this dependence provides detailed information about the shape of the OH dipole moment function, μ(r), and hence the absolute infrared transition strengths. In an accompanying paper we present the theoretical basis for extracting μ(r), for an open shell diatomic like OH, from relative infrared intensities and permanent dipole moment measurements (Peterson et al.). In this work we implement those ideas and determine the OH dipole moment function to be: μ(r)=1.6498(6) D+0.561(32) D/A(ring) (r−re )−0.75(17) D/A(ring)2 (r−re )−1.5(11) D/A(ring)3(r−re )3. The accuracy of μ(r) is excellent near re (re =0.970 A(ring)), since the data used to derive it are from low vibrational states. The useful range of this function extends from approximately 0.75 to 1.35 A(ring). The rotationless Einstein A coefficient for the OH fundamental is determined from μ(r) to be 16.7(19) Hz. This is in considerable disagreement with most other experimental and theoretical results, but is in good agreement with theoretical calculations by Mies (18.3 Hz) and by Langhoff et al. (13.8 Hz).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456451
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  • 8
    Electronic Resource
    Electronic Resource
    The near-infrared spectrum of ONNHF—direct evidence for geometric isomerism in a hydrogen bonded complex (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1450-1451 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The near-IR spectrum and equilibrium structure of a novel hydrogen bonded complex between nitrous oxide and hydrogen fluoride is described. In contrast to a previously reported structure, in which the HF bonds to the oxygen end of NNO, the present structure has the HF bonded to the nitrogen end of NNO. The structure is unambiguously confirmed by isotopic substitution. The identification of the two stable, spectroscopically distinct structures represents the first demonstration of geometric isomerism in a hydrogen-bonded complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453279
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  • 9
    Electronic Resource
    Electronic Resource
    Hindered internal rotation in jet cooled H2HF complexes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5621-5628 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibration–rotation spectrum of the HF stretch mode in ortho-H2HF complexes has been obtained via infrared laser direct absorption detection in a slit supersonic jet expansion. The spectrum resembles a Ka =1←1 parallel band of a prolate near-symmetric top and can be reasonably well fit with a Watson A-type Hamiltonian; however, no rigid molecular structure can reproduce the observed Ka splittings without invoking unphysically large changes in the constituent bond lengths upon complexation. The splittings are more correctly analyzed in terms of a j=1 hindered H2 rotor in an anisotropic potential, with a minimum energy T-shaped geometry. Matrix calculations determine barriers to H2 rotation between 120 and 170 cm−1 that depend systematically both on vibrational and rotational state in the complex. These data are consistent with a strong increase in potential anisotropy with decreasing intermolecular separation, with both upper and lower vibrational states close to the dissociation limit. No evidence for a corresponding Σ←Σ para-H2HF spectrum is observed, despite adequate experimental sensitivity. The matrix calculations indicate that the ground Σ state of para-H2HF is less stabilized by the potential anisotropy than the ground Π state in ortho-H2HF, and may therefore be much less efficiently formed in the jet expansion. The preferential observation of a ground Π vs Σ state in ortho-H2HF clearly indicates a minimum in the potential surface for a T-shaped vs collinear geometry. The observed rotational constants strongly suggest a H2⋅⋅⋅H–F ordering. The results provide direct evidence for vibrationally averaged structure, internal rigidity, and intermolecular bond strength that are significantly quantum state dependent, but can be qualitatively understood in terms of simple steric interactions between the H2 and HF subunits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453534
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  • 10
    Electronic Resource
    Electronic Resource
    High resolution IR laser spectroscopy of van der Waals complexes in slit supersonic jets: Observation and analysis of ν1, ν1+ν2, and ν1+2ν3 in ArHF (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4890-4902 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: IR spectra of jet cooled ArHF are obtained via direct absorption of a high resolution tunable difference frequency laser in a 2.54 cm path length, slit supersonic pulsed expansion at 〈10 K. Detection limits of 2×109 molecules/cm3/quantum state permit observation of the high frequency ν1 fundamental stretch (1000) ← (0000), the ν1+ν2 van der Waals bend plus stretch combination band (1110) ← (0000), as well as transitions to the (1002) triply vibrationally excited state that are weakly allowed via Coriolis interactions with the Π+ component of the (1110) manifold. The ground state (0000) molecular constants are in excellent agreement with previous microwave data. From the changes in rotational and centrifugal distortion constants, the vibrationally averaged van der Waals well depth is estimated to increase (+15%) with ν1 excitation, but decrease dramatically (−42%) upon subsequent excitation of the l=1 ν2 bend. L-doubling in the ν1+ν2 (1110) perpendicular bending state is large and negative [−69.8(18) MHz] and indicates the presence of a near resonant Coriolis coupledvibration of Σ+ symmetry at lower energy. A second, localized Coriolis perturbation is observed in the (1110) state and assigned to the near resonant (1002) Σ+ fundamental plus van der Waals stretch overtone at higher energy. Analysis of this Coriolis interaction indicates that coupling can be significant even for a three quantum change in vibration. However, a perturbative, small amplitude oscillator model predicts Coriolis matrix elements only 18% of the observed values, suggesting that large amplitude, bend–stretch interactions can strongly enhance Coriolis coupling. The decrease in the B rotational constant and the vibrationally averaged well depth upon ν2 excitation confirms the strong coupling between van der Waals stretch and bend coordinates. The slit expansion geometry quenches perpendicular velocity distributions and therefore offers intrinsically sub-Doppler resolution in an unskimmed molecular beam. Residual linewidths in the ArHF spectra are all below the apparatus resolution limit of ±25 MHz, which translates into a lower limit for the predissociation lifetime of 3 ns, i.e., in excess of 2×106 ν1 vibrational periods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451724
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