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  • 1
    Electronic Resource
    Electronic Resource
    Broad vibrational overtone linewidths in the 7νOH band of rotationally selected NH2OH (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9194-9196 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared–optical double-resonance spectroscopy of the 7νOH vibrational overtone level of NH2OH reveals 14 cm−1 wide spectral features. The product state distribution of the OH fragment subsequent to overtone excitation indicates that the 7νOH level of NH2OH is ∼128 cm−1 above the N–O bond dissociation energy. Comparison to HOOH overtone spectra at a similar excess energy suggests that the broad NH2OH linewidths result from vibrational state mixing at the 7νOH level and not from inhomogeneous structure or lifetime broadening of the dissociating molecules. The observation of 14 cm−1 overtone linewidths for a molecule the size of NH2OH suggests that the broad vibrational overtone transition linewidths in larger polyatomics may contain a substantial homogeneous component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459210
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  • 2
    Electronic Resource
    Electronic Resource
    Rotationally resolved vibrational overtone spectroscopy of hydrogen peroxide at chemically significant energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8620-8633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An infrared–optical double resonance scheme simplifies the room temperature 6νOH vibrational overtone spectrum of hydrogen peroxide and prepares highly excited reactant molecules in single rotational states for unimolecular reaction studies. First, an optical parametric oscillator excites the OH asymmetric stretch (ν5) and selects a single or small subset of rotational states. A visible dye laser pulse then promotes molecules from vOH=1 to vOH=6 where they subsequently dissociate to produce two OH fragments. A third laser detects the dissociation products via laser induced fluorescence. The rotationally resolved vibrational overtone spectra of hydrogen peroxide generated by scanning the visible dye laser frequency are assignable to a parallel band of a near prolate symmetric top. Linewidths of the individual rovibrational features range from 1–3 cm−1 but show no systematic dependence upon the rotational quantum numbers and are attributed predominantly to anharmonic coupling of the zeroth-order bright state to dark background states. The assignability of the double-resonance vibrational overtone spectra to J and K quantum numbers implies that K is conserved for at least a time determined by the linewidth of a single zeroth-order rovibrational feature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459249
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  • 3
    Electronic Resource
    Electronic Resource
    A new technique for state-to-state studies of unimolecular reactions (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4448-4450 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A double-resonance technique which combines infrared excitation of a fundamental vibration of a light atom oscillator with vibrational overtone excitation of that same oscillator selectively prepares molecules in individual quasibound vibrational–rotational states at energies above their dissociation threshold. A third laser probes individual states of the product fragments via laser induced fluorescence. We present our initial results applying this technique to study the 6νOH vibrational overtone spectroscopy and unimolecular dissociation dynamics of hydrogen peroxide (HOOH). The double-resonance approach simplifies the congested vibrational overtone spectrum of HOOH, and the linewidth of resolved features places a lower limit on the lifetime of approximately 7 ps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454782
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  • 4
    Electronic Resource
    Electronic Resource
    Unimolecular dissociation of hydrogen peroxide from single rovibrational states near threshold (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 889-898 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared-optical double resonance excitation of hydrogen peroxide using the ν3+ν5 and ν2 + ν5 combination bands as intermediate levels prepares reactant molecules in single rotational states near the OO dissociation threshold. The band origins of the ΔvOH = 4 vibrational overtone transitions originating from these combination bands provide information on the anharmonicities between the OH stretch and the OO stretch and OOH bend, respectively. At low resolution the vibrational overtone transitions are clearly parallel bands of a near prolate symmetric top and can be assigned to zeroth-order J and K quantum numbers. At 0.1 cm−1 resolution the individual features in the vibrational overtone spectra appear as clumps of sharp lines centered at the frequencies of the zeroth-order symmetric top transitions. The number of components within a clump appears to be less than the total number of available vibrational states. The narrowest feature observed has a linewidth of 0.12 cm−1 and sets a lower bound of ∼35 ps on the lifetime of the dissociating molecule. As J increases from 1 to 21, the clumps of lines coalesce into a smooth Lorentzian envelope. The overall clump width decreases with J, reaching an asymptotic value of 0.67 cm−1 at J(approximately-equal-to)17. A model incorporating a J dependent density of bath levels that couple to the zeroth-order bright state predicts the observed changes in the vibrational overtone transitions with J. The rotationally resolved vibrational overtone spectra provide information on the time scale for the conservation of K of the dissociating molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459979
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared spectrum of t-butyl hydroperoxide excited to the 4νOH vibrational overtone level (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1461-1465 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared predissociation spectrum of t-butyl hydroperoxide excited to the 4νOH level reveals extensive mixing between the zeroth-order OH stretch state and nearly isoenergetic zeroth-order dark states. Because most of these dark states have an OH stretch quantum number of zero, the predissociation spectrum strongly resembles the infrared spectrum of an unexcited molecule. The observed intensity distribution in the predissociation spectrum is what one would expect if the eigenstates prepared by 4νOH vibrational overtone excitation were statistical mixtures of all the nearly isoenergetic zeroth-order states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461060
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  • 6
    Electronic Resource
    Electronic Resource
    Torsion–rotation analysis of OH stretch overtone–torsion combination bands in methanol (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 91-100 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report rotationally resolved spectra of jet-cooled methanol for the OH stretch overtones, 2v1 and 3v1, and for the torsional combinations, 2v1+v12, 2v1+2v12, 3v1+v12, and 3v1+2v12. The spectra are obtained by direct excitation from the vibrational ground state with an infrared laser pulse. Population in the resulting upper state levels is detected by infrared laser assisted photofragment spectroscopy (IRLAPS). Global fits of the spectra to the Herbst Hamiltonian yield the torsional and rotational parameters, including F, ρ, V3, and V6, for each OH stretch excited state. For each quantum of OH stretch excitation, we find that the torsional barrier height V3 increases by 40.9±1.9 cm−1 and the torsional inertial F decreases by 0.89±0.02 cm−1. With reference to ab initio calculations, we explain the increase in V3 in terms of changes in the electronic structure of methanol as the OH bond is elongated. For Δv12=1 we observe only transitions with ΔK=±1, and for Δv12=2 we observe only ΔK=0. We present a Franck–Condon model to explain these apparent selection rules and the overall pattern of intensity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421357
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  • 7
    Electronic Resource
    Electronic Resource
    State-to-state studies of intramolecular energy transfer in highly excited HOOH(D): Dependencies on vibrational and rotational excitation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7461-7474 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use infrared-optical double resonance excitation, together with laser induced fluorescence (LIF) product detection, to measure rotationally resolved vibrational overtone spectra of hydrogen peroxide at energies up to 4500 cm−1 above the O–O dissociation threshold. The spectroscopic constants obtained from such spectra help characterize the potential energy surface and provide a stringent test for any theoretical representation thereof. Line profiles of individual rovibrational features provide information on the vibrational and rotational dependence of the intramolecular dynamics. Coupling to the manifold of optically inactive background states is independent of the total density of rovibrational states but rather controlled by specific low-order coupling terms in the Hamiltonian. Moreover, we find no significant difference in the IVR dynamics between states with all quanta in a single OH oscillator or distributed between the two local OH stretches. Finally, increasing rotation around the O–O pseudo-figure axis clearly enhances the IVR rate in most vibrational bands of H2O2 due to increased a-axis Coriolis coupling. Comparison to other OH stretch containing molecules allows us to define chromophore specific dynamics of this light atom oscillator. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481380
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  • 8
    Electronic Resource
    Electronic Resource
    Unimolecular reactions near threshold: The overtone vibration initiated decomposition of HOOH (5νOH) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1508-1520 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced fluorescence detection of the fragments from the unimolecular dissociation of hydrogen peroxide initiated by direct excitation of the fourth overtone of the OH stretching transition (5νOH) is a means of measuring both vibrational overtone predissociation spectra and populations of individual quantum states of the OH products. Because the excitation adds insufficient energy to break the OO bond, the measurements detect reactions of molecules that initially possess substantial thermal vibrational–rotational energy (≥1100 cm−1). The spectroscopic data, in which hot band and high energy transitions are particularly prominent, are fit by a vibrational–torsional model that adiabatically separates the low frequency torsional vibration from the higher frequency OH and OO stretching vibrations. The spectroscopic analysis shows that the effective trans barrier in the torsional potential increases by 75 cm−1 for each quantum of OH stretching excitation but decreases by 50 cm−1 upon excitation of the OO stretching vibration. The product state population distributions demonstrate that the lowest rotational level is preferentially populated in the unimolecular decomposition. This result is inconsistent with phase space theory, which predicts substantially more rotational excitation, but agrees with the statistical adiabatic channel model. The predictions of the latter model agree with the data for HOOH (5νOH) as well as with previous results for HOOH (6νOH). The statistical adiabatic channel model contains one parameter in addition to the ones required in phase space theory, and the value of this parameter that provides the best agreement with the measurements is consistent with an independent analysis of thermal recombination data. The experiment serves to test statistical calculations critically because it explores reactions near the threshold energy, where the predicted product state distributions are most sensitive to the details of the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450496
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  • 9
    Electronic Resource
    Electronic Resource
    Intramolecular energy transfer in highly vibrationally excited methanol. III. Rotational and torsional analysis (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11359-11367 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report here torsional analysis of rotationally resolved spectra of the 3ν1, 5ν1, and 6ν1 (OH stretch) bands of jet-cooled methanol. The upper states are reached by a double resonance excitation scheme involving the selection of single rotational states in the ν1 fundamental band. Detection of the overtone transitions (nν1←ν1) is by infrared laser assisted photofragment spectroscopy (IRLAPS). The torsional tunneling frequency declines monotonically from 9.1 cm−1 in the vibrational ground state to 1.6 cm−1 at 6ν1. For the available rotational levels at 3ν1 (K=0–3) and 6ν1 (K=0,1), the pattern of torsional energies is approximately regular. To obtain the vibrational dependence of the torsional barrier V3, it was necessary to use the OH radical and HOOH as models for the vibrational dependence of the torsional inertial constant F. The assumed linear dependence of V3 on ν1 accounts for the torsional tunneling splittings at v1=0, 3, and 6 and for the pattern of the torsional energies. V3 increases by 40–45 cm−1 per quantum of OH excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479076
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  • 10
    Electronic Resource
    Electronic Resource
    Intramolecular energy transfer in highly vibrationally excited methanol. II. Multiple time scales of energy redistribution (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11346-11358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-selected spectra of the OH stretch overtones of methanol in the range of v1=3–8 reveal spectral splittings and broadenings that result from vibrational couplings within the molecule. We employ a two-color excitation technique in which an infrared pulse promotes jet-cooled methanol molecules to a single rotational state in v1=1 or 2 and a second visible or near-infrared laser pulse is scanned to record a vibrational overtone spectrum. The final vibrationally excited species are detected by infrared laser assisted photofragment spectroscopy. The implications of the spectra for vibrational dynamics in the time domain can be understood in terms of a hypothetical coherent excitation of relevant portions of the spectrum. The observed splittings and widths correspond to three time scales. The largest splittings imply subpicosecond oscillation of energy between the OH stretch and a combination with the C–H stretch (5ν1(if and only if)4ν1+ν2 and 6ν1(if and only if)5ν1+ν2) or a combination with the COH bend (7ν1(if and only if)6ν1+2ν6). Secondary time scales correspond to finer splittings and are thought to arise from low-order resonances with other vibrational states. We argue that the nonmonotonic energy dependence of the presence and extent of such secondary structure throughout the recorded spectra reflects the requirement of resonance with important zeroth-order states. The third time scale, represented by the widths of the narrowest features at each overtone level, reflects the onset of vibrational energy randomization. These widths increase exponentially with vibrational energy in the range 2ν1 up to 8ν1. At the highest energy (25 000 cm−1) the three time scales begin to converge, implying an irreversible decay of the OH stretch overtone in 300 fs. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479075
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