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  • 1
    Electronic Resource
    Electronic Resource
    Spin uncoupling in 3A2 CS2 studied by high-resolution Zeeman and hyperfine quantum beat spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8761-8769 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The magnetic properties of the evsB2 spin component of the 3A2 state in the molecule CS2 have been investigated with a resolution of ∼100 kHz by quantum beat spectroscopy in a supersonic jet. Zeeman-level tuning in 12CS2 and 13CS2, providing Landé g factors, and measurements of the 13CS2 nuclear hyperfine structure were carried out, particularly to investigate their J dependence. Based on these results, it is proposed that both the magnetic moment and the hyperfine splitting are dominated by spin-uncoupling interactions, described in the rotational Hamiltonian by B(J−S).2 In addition, the g factors and rotational state lifetimes were used to provide spectroscopic assignments and to elucidate details of the state mixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462283
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  • 2
    Electronic Resource
    Electronic Resource
    Nuclear hyperfine structure in the electronic spectrum of propynal (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 187-196 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser-induced fluorescence spectrum of propynal (S1←S0) (A˜ 1A‘←X˜ 1A') has been investigated and a series of perturbations due to singlet–triplet coupling resolved. The singlet–triplet interaction matrix elements are of the order of 280 MHz. Fluorescence decays for both the mixed singlet–triplet eigenstates have been measured and are shown to contain quantum beats due to coherent excitation of nuclear hyperfine levels. This Doppler-free measurement in the time domain leads to an accurate determination of the nuclear hyperfine splittings produced by the two nonequivalent hydrogen atoms. The hyperfine structure has been analyzed for two rotational levels in the 91 vibrational state and gives the following values for combinations of the Fermi contact constants and dipole–dipole constants of the two protons in the pure triplet state: T1(a˜ 3A‘): A(1)FC+ 1/2 (T(1)xx−T(1)yy) ∼46 MHz; A(2)FC+ 1/2 (T(2)xx−T(2)yy) −4 MHz; T(1)zz∼T(2)zz ∼0 MHz. A simple model for the spin distribution in propynal predicts that the Fermi contact constant should be positive for the aldehydic proton and smaller and negative for the acetylenic proton and suggests that the Fermi contact constants make the dominant contribution to the effective hyperfine constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458461
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  • 3
    Electronic Resource
    Electronic Resource
    Rotational state dependence of radiationless transitions in S1 propynal (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4765-4771 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational state dependence of the radiationless processes of S1 propynal, HC≡CCHO, was investigated in three selected vibronic bands located at an excess energy of about 3000 cm−1 in a molecular beam using molecular quantum beat spectroscopy. The number of quantum beat frequencies counted in single rovibronic fluorescence decays shows a clear dependence on the rotational quantum number N of the excited rovibronic singlet state, reflecting an increase of the number of coupling triplet states nT by a factor of 4, from N=0 to 14. This increase is accompanied by a lengthening of the decay lifetimes by a factor of 3. Given eigenstate resolution, the effect of magnetic interactions in the triplet state is discussed and it is concluded that the N dependence is predominantly due to mixing of K states resulting in a symmetry breakdown. This mixing is proposed to be mainly induced by hyperfine interaction via the dipole–dipole term.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461832
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  • 4
    Electronic Resource
    Electronic Resource
    IRFI 042 reduces oxidative stress against kainic acid toxicity in the rat brain (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 85 (2003), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We investigated if IRFI 042, an analog of vitamin E, protects the brain against oxidative stress induced by intraperitoneal administration of Kainic acid (KA) (10 mg/kg); sham brain injury rats were used as controls. Animals received either IRFI 042 (20 mg/kg) or its vehicle 30 min before KA injection and after 6 h were sacrificed to measure malonildyaldheide (MDA) and glutathione levels (GSH) in the diencephalon. Behavioral changes were also monitored. Intraperitoneal administration of IRFI decreased MDA (micromol/g wet tissue: KA + vehicle = 22.5 ± 4.2; KA + IRFI = 17.1 ± 1; P 〈 0.005) and prevented GSH loss (nmol/g wet tissue: KA + vehicle = 0.41 ± 0.1; KA + IRFI = 1.86 ± 0.2; P 〈 0.005) in the diencephalon. The latency of occurrence of behavioral signs increased from 39 ± 1 to 62 ± 6 min in IRFI 042 group. The data suggest that IRFI 042 might protect against KA-induced oxidative stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.85.s2.19_1.x
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular quantum beats. High-resolution spectroscopy in the time domain (1992)
    s.l. : American Chemical Society
    Accounts of chemical research 25 (1992), S. 65-71 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00014a002
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum beat study of the nuclear hyperfine structure of OD and Ar⋅OD in their A 2Σ+ electronic states (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5365-5373 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear hyperfine structure of OD and Ar⋅OD in their A 2Σ+ electronic states has been studied by quantum beat spectroscopy. The very cold transient species were produced in a supersonic expansion using a pulsed discharge nozzle. Coherent excitation of hyperfine (hf) states, arising from one fine structure (OD) or rotational (Ar⋅OD) level, created quantum beats on the fluorescence decay. The beat frequencies, which correspond to energy separations between hf levels, could be measured to ±75 kHz. The splitting of the hf levels into their Zeeman components was investigated in a weak magnetic field. A fit of the zero field and Zeeman data yielded the relevant constants for the nuclear magnetic and electric quadrupole hyperfine interactions as well as the pertinent g-factors in each species. In the case of OD, the hf parameters agree well with those reported previously but are more accurately defined. For Ar⋅OD the previously unknown hyperfine and spin-rotation parameters of the A 2Σ+ state were determined. A comparison of the hf parameters in the two systems allowed assessment of the effect of van der Waals complex formation on the electron distribution. Thus complexation is found to reduce the unpaired electron density on the deuteron by 7% which is indicative of significant chemical bonding between the Ar atom and the OD moiety in the A 2Σ+ state of Ar⋅OD. For both systems, the g-factors gS and gl obtained suggest an admixture of other, possibly quartet, electronic states into the A 2Σ+ state. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471776
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  • 7
    Electronic Resource
    Electronic Resource
    The rotational state dependence of the dynamics of pyrimidine in the S1 (1B1) state studied by time resolved spectroscopy (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5890-5899 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of pyrimidine in three vibronic levels of the S1 (1B1) state with excess energies of 1100–1300 cm−1 above the 00 level has been studied by time resolved spectroscopy. The fluorescence decays from 40 to 50 single rovibronic levels in each vibronic band were measured and were found to be biexponential due to coupling with background triplet states. Analysis of the decays yielded the amplitude ratio of the fast (coherent) and slow (incoherent) component of the fluorescence intensity, A+/A−, and the lifetime of the slow component, being τ ≈700–900 ns. Both data show a clear dependence on the S1 rotational quantum number J. The A+/A− ratio, which reflects the number of coupled states, takes the form of a linear dependence on (2J+1) implying full rovibronic state mixing in the background 3B1 state. More states were found to be coupled than could be accounted for by the calculated background state density, suggesting further state mixing, possible mechanisms for which are discussed. The lifetime results were found to converge to limiting values at high J, the lifetime of the 3B1 state at the given energy. A small but significant difference (∼10%) in the lifetimes of the asymmetry doublets with Kc=1 was observed. Finally, a comparison of the rotational state dependent dynamics in pyrimidine with those in propynal and butynal is presented, pointing to a role for nuclear hyperfine interactions in dynamics. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469323
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational state distribution of CO photofragments from triplet ketene (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5101-5106 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nascent rotational state distribution of CO(v‘=0,J‘) following excimer laser photolysis of ketene at 351 nm has been determined under collisionless conditions in a flow cell. At this low excitation energy dissociation can only take place on the triplet potential surface leading to CH2(X˜ 3B1) and CO(X˜ 1Σ+). The available energy permits only the vibrational ground state of CO to be populated. The observed rotational distribution of CO(v‘=0,J‘) deviates drastically from a phase space theory statistical distribution as well as from a thermal one. A Boltzmann plot of this distribution exhibits a population inversion for J‘〈13. The nonstatistical behavior is attributed to a barrier along the dissociation path. The fragments are repelled too rapidly for energy to be randomized between them. Thus the photofragmentation dynamics of triplet ketene contrasts markedly with dissociation on the singlet surface which has no barrier and gives a statistical CO rotational state distribution. An impulsive model calculation for the ab initio transition state geometry is in surprisingly good agreement with the experimental energy partitioning among the fragment degrees of freedom. This suggests that the CCO bond angle is strongly bent at the top of the barrier and that the barrier height is a substantial fraction of available energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451702
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  • 9
    Electronic Resource
    Electronic Resource
    Excited state dipole moments in a polyatomic molecule determined by Stark quantum beat spectroscopy (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 696-704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution Stark quantum beat spectroscopy is demonstrated to be a powerful method to determine magnitude and orientation of excited state dipole moments in asymmetric polyatomic molecules. We measured the dipole moments μ of the vibrationless S1 state of planar propynal and αD-propynal in a pulsed supersonic jet and determined both components of the μ vector in the molecular plane: μ'a=0.874(10)D, μb=1.06(2)D, ||μ'||=1.374(22) D for HC≡CCHO; μ'a=0.863(10)D, μb=1.04(1) D ||μ'||=1.351(14) D for HC≡CCDO. The results are related with recently reported microwave data of the ground state dipole moment μ(S0) and are interpreted in terms of electron delocalization from the carbonyl group to the ethinyl moiety. The dipole moments of S0 and S1 propynal are oriented essentially along the CO bond. The applicability of the Stark quantum beat technique to polyatomic molecules is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454198
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  • 10
    Electronic Resource
    Electronic Resource
    Hyperfine quantum beats and Zeeman spectroscopy in the polyatomic molecule propynal HC≡CCHO (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 3755-3767 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum beats in the fluorescence decay of two single rovibronic levels of optically excited propynal (HC≡CCHO) have been measured in a supersonic jet apparatus. The complex beat pattern was explored using laser light of linear and circular polarization under zero-field conditions (nulled earth magnetic field) or in conjunction with an applied magnetic field. Theoretical aspects of molecular quantum beats were derived which include hyperfine coupling, magnetic field effects, and polarized excitation and detection. Singlet–triplet coupling matrix elements, Landé g-factors of the triplet hyperfine levels, and singlet and triplet decay rates have been determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449138
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