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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Laser spectroscopy of crossed molecular beams: The dissociation energy of BaI from energy-balance measurements (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8544-8556 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Through application of energy-balance arguments to the crossed-beam reaction Ba(1S0)+HI(X 1Σ+) →BaI(X 2Σ+) +H(2S1/2), a lower limit for the BaI bond dissociation energy is determined to be D00(BaI) (approximately-greater-than)76.8±1.7 kcal/mol (3.33±0.07 eV). Based on the upper bound of D00(BaI) (approximately-less-than)78.5±0.5 kcal/mol, as determined from earlier predissociation studies [M. A. Johnson, J. Allison, and R. N. Zare, J. Chem. Phys. 85, 5723 (1986)], we recommend a BaI bond strength of 77.7±2.0 kcal/mol (3.37±0.09 eV). This dissociation energy is more than 5 kcal/mol higher than the previously accepted value of D00(BaI) as derived from mass spectrometric measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459292
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Rotational relaxation in the H2CO A˜ 1A2 state by transient gain spectroscopy (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5755-5756 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new, pulsed pump–cw probe technique, transient gain spectroscopy, has been used to measure the zero pressure lifetime (279±10 ns) and self-collision depopulation rate (110.5±3.1 μs−1 Torr−1) for the H2CO A˜ 1A2 41 JKa,Kc =132,12 level as well as the 122,11←132,12(31±8 μs−1 Torr−1) and 142,13←132,12(40±6 μs−1 Torr−1) rotational relaxation rates. The dominant collisional process is rotational energy transfer, which, for the H2CO(A˜)+H2CO(X˜) process examined here, appears to follow dipole–dipole scaling and propensity rules. The 110.5 μs−1 Torr−1 depopulation rate in the A˜ state agrees with the vibrationless X˜ state rate obtained from microwave power broadening scaled by the 1.46 D/2.33 D electric dipole moment ratio. The two strongest a-dipole rotational state-to-state rates account for more than 50% of the total removal rate from H2CO A˜ 41 132,12.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448564
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  • 7
    Electronic Resource
    Electronic Resource
    The vibronically-resolved emission spectrum of disulfur monoxide (S2O): An algebraic calculation and quantitative interpretation of Franck–Condon transition intensities (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5038-5055 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Emission spectra obtained from jet-cooled disulfur monoxide (S2O) molecules have been interpreted by means of a novel Lie algebraic formalism that makes possible the facile evaluation of multidimensional Franck–Condon factors. Fluorescence accompanying selective excitation of isolated vibronic bands in the S2O C˜ 1A′←X˜ 1A′(π*←π) absorption system has been dispersed under moderate spectral resolution, allowing assignment of ground state levels possessing up to 20 quanta of vibration in the ν2 S–S stretching mode [Evib(X˜)≤13 900 cm−1]. Aside from providing a rigorous and economical description for the inherently anharmonic nature of highly-excited polyatomic species, our algebraic approach enables quantitative information on molecular wavefunctions to be extracted directly from spectroscopic data. The emerging picture of S2O vibrational dynamics suggests that the X˜ 1A′ potential surface is substantially more "local" in character than the C˜ 1A′ manifold. While the observed pattern of X˜ 1A′ vibrational energies could be reproduced well through use of model Hamiltonians that include only diagonal anharmonicities in the local algebraic basis, successful treatment of the C˜ 1A′ state necessitated explicit incorporation of off-diagonal anharmonicities that lead to pervasive mixing of local vibrational character. This disparate behavior is manifest strongly in measured C˜–X˜ transition strengths, thereby allowing detailed investigations of Franck–Condon intensities to discern the underlying dynamics. Structural parameters deduced from algebraic analyses are in good accord with previous predictions of the change in S2O geometry accompanying π*←π excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479786
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  • 8
    Electronic Resource
    Electronic Resource
    Detection of stimulated emission pumping via degenerate four-wave mixing (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1640-1643 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The stimulated emission pumping (SEP) process has been detected by means of a newly developed zero-background scheme based upon the Doppler-free technique of degenerate four-wave mixing (DFWM) spectroscopy. Rotationally resolved SEP-DFWM spectra recorded for the (02000) vibrational level of CS2 X˜ 1∑+g exhibit signal-to-noise ratios approaching 1000:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462149
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