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  • 1
    Electronic Resource
    Electronic Resource
    Far-infrared laser magnetic resonance detection of fluorine dioxide (FO2) (1983)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 5068-5070 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150643a007
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of the reactions of methylene (X3B1)-radicals with nitric oxide and nitrogen dioxide (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 1070-1073 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100340a011
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  • 3
    Electronic Resource
    Electronic Resource
    Stimulated emission pumping spectroscopy of CH3O (X˜ 2E) at the dissociation limit (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1472-1473 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-lying rotation vibration states of CH3O (X˜ 2E) radicals have been studied close to the threshold energies for the unimolecular reactions CH3O→H2CO+H and CH3O→CH2OH using the technique of stimulated emission pumping (SEP) spectroscopy. Spectra were recorded with the PUMP laser tuned to the rR21(7.5,−5) rotational lines of the A˜ 2A1←X˜ 2E 000 and 310 vibrational bands and the DUMP scanned to access X˜ levels in the energy region 3000 cm−1≤Evr≤9000 cm−1. The transitions to highly excited X˜ rovibrational levels as opposed to two photon resonances to a higher electronic state was proved by the virtual identity of the SEP spectra, plotted vs term energy, with the PUMP tuned to the two A˜ intermediate levels. The spectra show evidence for strong rovibronic level mixing. At Evr≈6300 cm−1, where the calculated total harmonic vibrational density of states is ρv,h≈0.43 cm−1, close to every CH3O vibrational state can be observed in the spectrum. The highest excitation energy which was reached so far (Evr≈9000 cm−1) exceeds the H–CH2O dissociation energy, ΔH0R,0K≈6800 cm−1. The observations provide the basis for a study of the unimolecular dissociation of CH3O at a fully quantum state resolved level of detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459157
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  • 4
    Electronic Resource
    Electronic Resource
    Collisional relaxation of H2CO (A˜ 1A2, v4=1, JKa ,Kc=132,12) by He, Ar, Xe, and N2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1008-1011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The collision-induced deactivation of H2CO in a specific rotational level in its first electronically excited singlet state, A˜ 1A2, v4=1, JKa,Kc=132,12, has been investigated with a series of colliders, M=He, Ar, Xe, and N2. The target level was populated via the transition A˜←X˜, 410, 132,12←133,11 using a pulsed dye laser. The subsequent relaxation was monitored using the technique of transient gain spectroscopy (TGS) via the transition A˜→X˜, 201301414, 132,12→131,13, which coincides with the line of an Ar+ laser at λ=488.0 nm. The experiments yielded the overall collisional depopulation rate constants (velocity averaged cross sections) for He, Ar, Xe, and N2, respectively: (5.25±0.20)×10−10 cm3/molecule s (39 A(ring)2), (5.22±0.18)×10−10 cm3/molecule s (86 A(ring)2), (5.37±0.29)×10−10 cm3/molecule s (106 A(ring)2), (8.25±0.29)×10−10 cm3/molecule s (125 A(ring)2), where the uncertainties correspond to the 2σ standard deviations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457224
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  • 5
    Electronic Resource
    Electronic Resource
    Polarization-detected transient gain studies of relaxation processes in v4=1 A˜ 1A2 formaldehyde-h2 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4819-4833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polarization-detected transient gain spectroscopy (PTGS), a time-resolved PUMP/PROBE scheme with single rotation–vibration level selectivity in both preparative and monitoring stages, has been used to study total depopulation and rotational state-to-state rates in the H2CO A˜ 1A2 v4=1 vibrational level. For H2CO(A˜)/H2CO(X˜) collisions, single rovibronic level depopulation rates in the range 88±2 to 127±6 μs−1 Torr−1 (∼10 times faster than the hard sphere gas kinetic rate) were obtained from Stern–Volmer plots which were found to be linear over at least the 0.02–0.2 Torr pressure region. Rotational relaxation between the 50,5 and 60,6 eigenstates reflects a-dipole propensity rules with the sum of first order ΔJ=+1 and ΔJ=−1 processes accounting for well over 50% of the total removal cross section measured for a single rovibronic level. The agreement between collisional decay rates for the 132,12 eigenstate measured previously by the TGS technique and here by PTGS, 110±3 and 106±4 μs−1 Torr−1, respectively, suggests that elastic reorientation processes (ΔJ=ΔKa =ΔKc =0, ΔM≠0) occur with much less efficiency than inelastic energy transfer. Collisional depopulation from single rotational levels of H2CO A˜ 1A2 v4=1 is a remarkably efficient process, but completely understandable in the small molecule, isolated binary collision limit. None of the multiexponential decay and nonlinear Stern–Volmer effects manifest in previous undispersed fluorescence studies remain when PTGS is used to populate and monitor a single rovibronic level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454694
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  • 6
    Electronic Resource
    Electronic Resource
    Collision-induced intersystem crossing of CH2 from a˜ 1A1 to X˜ 3B1: A case study of the mixed-state model (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1058-1072 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate coefficients for collision-induced intersystem crossing (CIISC) of methylene from the a˜ 1A1 first excited to the X˜ 3B1 ground electronic state, CH2 (a˜ 1A1)+M→CH2 (X˜ 3B1)+M, were investigated within the framework of the mixed-state mechanism [see, e.g., K. F. Freed, in Potential Energy Surfaces, edited by K. P. Law (Wiley, New York, 1980)]. Accordingly, the overall electronic relaxation was assumed to proceed via a sequence of rotational transitions within the a˜ manifold and allowed transitions from the a˜ to the X˜ manifold originating via "gate'' states of a˜ which are states that contain some triplet character due to spin–orbit coupling with nearby X˜ rovibrational states. The perturbed a˜ and perturbing X˜ levels and relevant interaction matrix elements were identified from the available spectroscopic data. Rate coefficients for rotational relaxation processes were obtained from collision broadening measurements of CH2 (X˜) far-infrared laser magnetic resonance (FIR-LMR) transitions. Taking these data, thermal CIISC rate constants corresponding to experimental results for the overall depletion of rotationally thermalized CH2 (a˜) and build up of (X˜) by M were evaluated for twelve interesting collision partners (M=He, Ne, Ar, Kr, Xe, N2, SF6, H2, D2, CH4, C2H6, H2O), taking into account every single CH2 (a˜) rotation vibration state with energies up to Evr≤900 cm−1. The results were found to be in good agreement with reported room-temperature experimental data. Temperature dependencies, which were predicted for M=Ar, N2, and CH4, also agree with measured values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464330
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  • 7
    Electronic Resource
    Electronic Resource
    Stimulated emission pumping spectroscopy of CH3O (X˜ 2E, ν6): New observations on the Jahn–Teller effect (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4297-4300 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experiments have been carried out using hot band laser induced fluorescence (LIF) excitation and stimulated emission pumping (SEP) spectroscopy to characterize the excited doubly degenerate ν6 vibrational mode of CH3O (X˜ 2E) which is of interest with respect to the Jahn–Teller effect in the molecule. Rotationally resolved spectra were recorded for the A˜ 2A1↔X˜ 2E, 610 and 310610 bands. The observed line structures indicate that these bands must be assigned to Δj=3/2 parallel (ΔK=0) vibronic bands. No evidence could yet be obtained for the corresponding Δj=1/2 vibronic transitions assumed previously. The results imply that the linear Jahn–Teller effect for ν6 is very small. Instead, coupling between the A˜ 2A1 and the X˜ 2E states by a pseudo-Jahn–Teller interaction operator is suggested as a plausible mechanism for the observation of the forbidden transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465036
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  • 8
    Electronic Resource
    Electronic Resource
    Direct measurements of state specific unimolecular dissociation rate constants of highly excited single rotation vibration quantum states of CH3O (X˜ 2E) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2271-2274 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibration rotation quantum state resolved unimolecular dissociation lifetimes of highly excited CH3O (X˜ 2E) molecules have been measured using the method of stimulated emission pumping (SEP) in connection with transient laser induced fluorescence (TLIF) excitation spectroscopy for preparing selected single target states and for their time resolved detection. The measured decay rate constants for six closely spaced levels with precisely known total excitation energies around E(X˜)≈7450 cm−1 and J=0.5 (or 1.5) were found to vary erratically between 9⋅105 s−1≤k≤3⋅107 s−1. The results are compared to predictions by unimolecular rate theory and discussed with respect to the question of mode specific vs statistical reactivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465239
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  • 9
    Electronic Resource
    Electronic Resource
    Rotation–vibration state resolved unimolecular dynamics of highly vibrationally excited CH3O (X˜ 2E). I. Observed stimulated emission pumping spectra (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3618-3633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the technique of stimulated emission pumping (SEP) spectroscopy, highly excited vibration–rotation states of the CH3O (X˜ 2E) molecule were probed up to energies of E≤10 000 cm−1. The highest excitation energies exceed the asymptotic H–H2CO dissociation limit of the molecule [ΔrH00(H–H2CO)≈6900 cm−1]. Work was carried out at different experimental resolutions. First, low resolution survey SEP spectra were found to exhibit persistent vibrational structure up to energies far above the dissociation limit. The observed main features were found to be assignable, in a zero-order picture that leaves aside possible mode-to-mode couplings, to the progression of the excited C–O stretch vibration states (ν3). The widths of the respective features correspond to localized short-time vibrational motion for times of ≥0.3 ps (≥10 C–O vibrational periods). Second, in high resolution scans over the coarse vibrational features, characteristic clumps of individual vibration–rotation eigenstates were revealed. These clumps are ascribed to distinctive Franck–Condon active bright zero-order levels which are mixed with the large number of Franck–Condon inactive dark bath states. Under carefully selected conditions, the clumps could be attributed to states with defined and well known values of the total angular momentum quantum number J, which remains as a good quantum number in different coupling cases. These clump spectra will be analyzed quantitatively in the following paper with respect to their bearing for the intramolecular vibrational dynamics of highly excited CH3O (X˜) as a function of vibrational and rotational excitation. From the observed spectra, quantitative data can be obtained on the rate and extent of collision-free intramolecular vibrational and rovibrational energy redistribution (IVR and IRVR) processes, which would result after coherent ultrashort pulse excitation of the molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467547
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  • 10
    Electronic Resource
    Electronic Resource
    Rotation–vibration state resolved unimolecular dynamics of highly excited CH3O (X˜ 2E). II. Intramolecular vibrational dynamics of excited "C–O stretch'' states (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3634-3648 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The stimulated emission pumping (SEP) spectra of highly excited CH3O (X˜ 2E) reported in the preceding paper [A. Geers, J. Kappert, F. Temps, and J. Wiebrecht, J. Chem. Phys. 101, 3618 (1994); paper I] are analyzed to extract quantitative data on the collision-free intramolecular vibrational dynamics of the molecules. Attention is focused on the spectra and dynamics of the excited C–O stretch vibration (ν3) states at energies between 3 000 cm−1≤E≤10 000 cm−1. The spectra are found to exhibit a rather sudden transition at E≈5000 cm−1 from the regular, assignable properties at low energies to the "statistical'' region at high energies. This IVR "threshold'' is approximately 2000 cm−1 below the asymptotic H–H2CO dissociation limit of the molecule. The observed densities of states at these energies approach the full J- and symmetry-sorted rovibronic densities estimated from harmonic state counts. The nearest-neighbor level spacing distribution in the spectra and the magnitude of the inferred root mean square level coupling matrix elements support the assumption of nearly "ergodic'' molecular properties in this region. From computed time autocorrelation functions, the IVR lifetimes of the highly excited C–O stretch states are found to be of the order of τ≈0.2–0.3 ps (v3=5 to 6). Evidence is obtained from some spectra for two-tier IVR processes with characteristic time scales of 0.2 and 2 ps, respectively. The highest excited C–O stretch states at energies above ≈8000 cm−1 (v3≥8) appear to be coupled only weakly to neighboring background states. This last observation hints at the existence of quasistable periodic orbits, which are embedded in the quasicontinuum of dissociative states at these energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468412
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