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  • 1
    Electronic Resource
    Electronic Resource
    Broad spectral features in the stimulated emission pumping spectrum of acetylene (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5972-5974 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational spectrumof acetylene is reported. This is the stimulat emission pumping spectrum obtained by stimulated downward transition from an upper electronic state to the ground electronic surface.Broad band and high resolution spectra were recorded at 25840−27250 wave numbers.(AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454510
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  • 2
    Electronic Resource
    Electronic Resource
    High resolution spectroscopic detection of acetylene–vinylidene isomerization by spectral cross correlation (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3976-3987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Information about the unimolecular acetylene (HC 3/4 CH)↔vinylidene (H2C=C:) isomerization on the S0 energy surface has been extracted from vibrationally unassigned high resolution stimulated emission pumping (SEP) spectra of acetylene. The combination of a new pattern recognition scheme, spectral cross correlation (SCC) with complete nuclear permutation-inversion (CNPI) group theory is shown to be a powerful new technique for characterizing bond rearrangement in highly vibrationally excited normally rigid polyatomic molecules. SCC detects isomerization "resonances'' which destroy an approximate vibrational symmetry (e.g., the number of cis-bending quanta). The energies (relative to the zero point level of the stablest isomer) and widths of such resonances provide information about the "energies'' of isomer rovibrational levels and the isomer-level-specific isomerization rate. Vinylidene isomerization resonances may be distinguished from ordinary acetylene Fermi or Coriolis perturbations by a unique rotational symmetry dependence due to the correlation between acetylene [D∞h(M)] and vinylidene [C2v(M)] levels in the CNPI group G8. An SCC map of the HCCH S0 15 000–15 900 cm−1 energy region above the zero point level was obtained by comparing SEP spectra recorded via S1(A˜ 1Au)33 and 2162 Ka=1 intermediate levels. The predicted rotational symmetry dependence of the SCC was found between 15 410–15 640 cm−1, but the vinylidene resonance line shape was obscured by Franck–Condon interference effects from well known perturbations between the 33 and 2162 SEP intermediate levels. It was therefore not yet possible to determine the height of the isomerization barrier (or even whether a barrier exists) but an upper bound for the vinylidene zero point level of 15 525 cm−1 was inferred from the SCC data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456828
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    High resolution vacuum ultraviolet fluorescence excitation spectrum and predissociation of A˜ 1A‘ HCN (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3988-3989 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜–X˜ fluorescence excitation spectrum of HCN has been recorded using 4-wave mixing in Sr vapor as a tunable vacuum ultraviolet source. The excitation spectra are notable for the high signal to noise ratio, resolution (FWHM ∼0.3 cm−1) of nearly all previously blended lines, and accuracy of wavelength calibration (±0.03 cm−1). Measured lifetimes for the first three bending levels of the A˜ state [τ(000)1=13±7 ns, τ(010)1=130±24 ns, and τ(020)1〈2 ns] qualitatively confirm the results of Hsu, Smith, and Wallace [Chem. Phys. Lett. 111, 219 (1984)]. Stern–Volmer fluorescence quenching studies reported here yield a best fit quenching constant for the A˜(000)1 rotational levels of Kq =73/μs⋅Torr, which is similar to the quenching constant of the A˜(010)1 level (Kq =24.3±0.4/μs⋅Torr).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457809
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  • 5
    Electronic Resource
    Electronic Resource
    Multiphoton ionization of O2 X 3Σ−g, a 1Δg, and b 1Σ+g via the two-photon resonant nsσg, ndσg, and ndπg Rydberg levels (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5185-5200 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiphoton ionization spectra have been obtained and analyzed for excitation in the 215–360 nm region from the X 3Σ−g, a 1Δg, and b 1Σ+g states of O2. The 0–0 band of the C 1Πg state is reported for the first time. Measurements of other vibrational bands terminating in the C 3Πg and d 1Πg states are in good agreement with determinations by other groups. Several vibrational levels (v'=0–5) of the 3dπg Rydberg complex have been assigned on the basis of (1) an analysis of the spin–orbit couplings between the (Λ,S) basis-set states, (2) spectral simulation, and (3) the behavior of the states when the excitation radiation is changed from linear to circular polarization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457589
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  • 6
    Electronic Resource
    Electronic Resource
    High precision dipole moments in A˜ 1A2 formaldehyde determined via Stark quantum beat spectroscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4150-4167 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution technique of Stark quantum beat spectroscopy is used to examine the electric dipole moment function for the first excited singlet state (A˜ 1A2) of formaldehyde-h2 and formaldehyde-d2. The high precision of these measurements (i.e., better than 5 parts in 104) enables detailed determination of a-axis dipole moment components (μa ) for individual J=2 rovibronic levels in the ν4 out-of-plane bending mode. In the case of 21,1 rotational levels, we find μa (40)=1.4784(7) D and μa (41)=1.4678(4) D for H2CO. For D2CO the measured 21,1 dipole moments are μa (40)=1.4698(6) D, μa (41)=1.4693(3) D, and μa (43) =1.4786(7) D. The state-specific variations in μa revealed by this study reflect the structural influences exerted by the pervasive S1∼S0 nonadiabatic interactions and the pyramidally distorted equilibrium configuration which characterize the A˜ state of formaldehyde. The origin and experimental manifestation of the out-of-plane dipole moment component (μc ) in nonrigid A˜ 1A2 formaldehyde is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455773
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A nomenclature for Λ-doublet levels in rotating linear molecules (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1749-1753 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is proposed that the two Λ-doublet levels of linear molecules with nonzero electronic orbital angular momentum be labeled Λ(A') and Λ(A‘), e.g., Π(A') and Π(A‘) for Π states, etc., according to the following prescription: All series of levels in which the electronic wave function at high J is symmetric with reflection of the spatial coordinates of the electrons in the plane of rotation will be designated Λ(A') for all values of J, and all those for which the electronic wave function is antisymmetric with respect to reflection will be denoted Λ(A‘). It is emphasized that this notation is meant to supplement, and not replace, the accepted spectroscopic e/f labeling and the parity quantum number. The utility of the Λ(A')/Λ(A‘) notation is that it is of most relevance in the mechanistic interpretation of reactive or photodissociative processes involving open-shell molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455121
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  • 9
    Electronic Resource
    Electronic Resource
    Collisional energy transfer in highly vibrationally excited H2CO(X˜ 1A1) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1895-1897 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional energy transfer has been investigated in highly vibrationally excited H2CO (X˜ 1A1) at Evib≅11 400 cm−1 using the method of stimulated emission pumping–transient absorption spectroscopy (SEP-TAS). Total depopulation and state-to-state rate constants were measured for several rotational levels of the 2444 vibrational state. For H2CO self-relaxation the depopulation rate constant of the 61,5 level was measured to be k0=(3.12±0.13)×10−9 cm3/molecule s. An analysis of the state-to-state data with a simplified master equation approach yielded rate constants k1=(7.7±1.2)×10−10, k2=(1.2±0.3)×10−10, and k3=(0.6±0.3)×10−10 cm3/molecule s for collisions with ΔJ=1, 2, and 3, respectively, and ΔKa=0, ΔKc=ΔJ, the reverse rate constants being given by microscopic reversibility. Thus, the ΔJ=±1 steps account for ∼50% of all inelastic collisions, which can be rationalized in terms of a simple dipole–dipole interaction. At Evib≅11 400 cm−1, where ρvib≅0.42/cm−1, collisions seem to conserve the vibrational character in spite of the fact that the energy gap between adjacent vibrational states is a fraction of the transferred rotational energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453207
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  • 10
    Electronic Resource
    Electronic Resource
    The electric dipole moment of NiH X 2Δ5/2 and B 2Δ5/2 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4717-4718 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A sputter source/supersonic jet apparatus has been developed in order to record MJ-resolved Stark spectra of refractory diatomic molecules. Dipole moments of 0.3±0.1 and 2.4±0.1 D have been measured for the NiH B 2Δ5/2(v=1) and X 2Δ5/2(v=0) levels from resolved splittings of the Q(2.5) and R(2.5) lines at 17 462.95 and 17 500.50 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448682
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