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  • 11
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 91 (1987), S. 506-508 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3692-3708 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of OCS in the region from 222–248 nm has been investigated by monitoring the CO and S(1D2) primary photoproducts; as well as the secondary production of S(3P2), S(3P1), and S(3P0) using fluorescence induced by a tunable vacuum ultraviolet laser source based on four-wave mixing in magnesium vapor. The quantum yield of S(3P) was found to be 0.00±0.02 at 222 nm. Thus, in contrast to our preliminary report, the present more detailed investigation shows that the sole sulfur product appears to be S(1D). The CO photofragment is produced almost exclusively in v=0 [CO(v=1)/ CO(v=0)≤0.02], but the rotational distribution is inverted and peaked at very high rotational levels. The peak shifts from J=56 for dissociation at 222 nm to J=31 at 248 nm. Doppler profiles of the CO rotational transitions reveal (1) that all observed levels are produced in coincidence with S(1D), (2) that for 222 nm photolysis the fragment recoil anisotropy shifts from a distribution characterized by β=1.9 at J=67 toward one characterized by β=0 near J=54, (3) that the CO velocity vector is aligned nearly perpendicular to its angular momentum vector, and (4) that the CO angular momentum vector is also aligned parallel to that component of the transition dipole which lies perpendicular to the recoil velocity. These results are interpreted in terms of a model for the dissociation in which excitation takes place to two surfaces of A' and A‘ symmetry derived from a bent 1Δ configuration. Dissociation of OCS clusters was also investigated and was found to produce a photochemistry completely different from that of the monomers. Rotationally cold CO as well as S2 in both the X3Σ−g and a1Δg states was observed.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3261-3268 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 193 nm dissociation of CS2 has been studied under supersonic molecular beam conditions, with the atomic S products detected by vacuum ultraviolet laser-induced fluorescence. These experiments measure the branching ratio between singlet and triplet channels to be S(3P)/S(1D) =2.8±0.3. Doppler spectroscopy on the S(3P2) and S(1D2) products was used to study the dynamics of each channel separately. The energy release in each channel was similar, with the CS fragments formed vibrationally inverted with about 50% of the available energy in CS rotation and vibration. The recoil velocity anisotropy in each channel was also measured, found to be the same for both, and was consistent with a 2 ps lifetime for the 1Σ+u(1B2) excited state of CS2.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1258-1268 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of glyoxal has been investigated by monitoring the CO internal energy distribution using tunable vacuum ultraviolet laser-induced fluorescence on the A←X system. Appearance times for the CO are in excellent agreement with the glyoxal fluorescence decay times, indicating that there is no long-lived intermediate in the dissociation. The quantum yield for CO production is independent of the K quantum number describing the glyoxal rotation. The CO is formed almost entirely in v=0 but is spread over a broadly excited rotational distribution peaking at J(approximately-equal-to)42. Analysis of the CO Doppler profiles shows that the velocity of the CO increases with increasing rotational level and that the CO recoil velocity vector is oriented predominantly perpendicular to its angular momentum vector. These observations, which are in agreement with both previous time-of-flight data and molecular orbital calculations, are consistent with a model for the dissociation involving planar intermediates for the two channels leading to CO+H2CO or to 2 CO+H2. It appears that the highest rotational levels of CO are produced in coincidence with the H2CO channel.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7106-7113 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The zero kinetic energy (ZEKE) photoelectron spectrum of nitrogen has been recorded using coherent vacuum ultraviolet light for single-photon excitation to the various ionization thresholds. Ionization thresholds from the lowest (15.58 eV) to 17.7 eV were studied. In this energy range, both Franck–Condon allowed (v+=0 and 1) and Franck–Condon forbidden (v+=4, 5, 6, and 8) levels of the N2+ X 2∑g+ ground electronic state were studied. The rotational intensities of these bands were studied, and a comparison made with previous ab initio work on the photoionization of N2. The role of complex resonances in the alteration of rotational linestrengths is discussed with reference to a high resolution photoionization spectrum recorded in the region of the v+=1 threshold. It was also possible to compare the relative intensities of all of these vibrational bands, to investigate the mechanism for observation of Franck–Condon forbidden vibrational bands in ZEKE spectroscopy. These results are discussed in terms of resonant autoionization, which is commonly observed in threshold photoelectron spectroscopy. The v+=0, 1, 2, and 4 levels of the A 2∏u excited state of N2+ were also studied, and the rotational structure was compared with ab initio and experimental results for the same state in the isoelectronic system, CO+. The band intensities were also measured, and compared with the Franck–Condon factors for excitation to the A state vibrational levels for the v=0 state of N2. A comparison with the v+=0 band of the X state is used to obtain an estimate of the relative signal yield for these excited state thresholds. For most of the bands observed in the present study, there are previous lower resolution threshold photoelectron spectra recorded using synchrotron radiation, and a comparison is made with these previous results. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1733-1742 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Interactions between the B' 2Δ non-Rydberg state and nearby 2Δ Rydberg states of NO have been studied by vacuum ultraviolet laser-induced fluorescence spectroscopy. By using tunable, coherent radiation in the 60 000–70 000 cm−1 range, NO molecules in a supersonic jet were excited and their radiative decay was monitored by time-resolved fluorescence detection. In this way accurate, collision-free radiative lifetimes were measured for several levels of the B' 2Δ, F 2Δ, N 2Δ, and D 2Σ+ excited states of NO. Using these lifetimes the oscillator strengths for the B'–X and F–X transitions were calculated. The radiative lifetimes for the perturbed states were quite different from the unperturbed lifetimes, and these changes are discussed in terms of the known interactions between states in this spectral region. For the unperturbed vibrational levels of the B' 2Δ state, radiative lifetimes between 129–139 ns were measured, while for the F 2Δ state, a radiative lifetime of 30 ns was measured. For the perturbed bands of the F2Δ and B' 2Δ states, the radiative lifetimes were accurately described by a two-state homogeneous perturbation model, but for the B'(v=7)∼N(v=0) mixed states, the lifetimes were dramatically different from those expected on the basis of two interacting states. This is caused by a third-interacting state whose identity is not known. The B'(v=8,9) states, while having unperturbed line positions, have shorter radiative lifetimes, indicating the onset of predissociation in those levels.
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8476-8484 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (1+1) resonance enhanced multiphoton ionization spectra of jet-cooled CS2 were obtained between 45 500 and 48 000 cm−1 (220–208 nm) for the two isotopomers 12C32S2 and 12C34S32S. With the use of different expansion gases which resulted in varying degrees of vibrational cooling and the comparison of the two isotopomer spectra, a partial assignment of the C˜ 1B2–X˜ 1Σg+ transition was obtained. The electronic origin of this transition is confirmed to lie at 46 248.7 cm−1 and values for the predissociation lifetimes for the upper state for 34 vibrational bands and isotopomer shifts of seven vibrational levels of the 1B2 state are presented. The lifetimes of the Σ0 bands were found to be larger than those of corresponding Π1 and Δ2 bands. A simulation of the spectrum, which used the harmonic approximation, is in qualitative agreement with the band positions and shifts, but quantitative disagreement between the values leads us to conclude that a normal mode analysis is not appropriate to describe the low vibrational levels of the 1B2 state. The results presented increase our understanding of the low-lying predissociating levels of CS2, which will be of use in future photofragment studies. © 1999 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8139-8142 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (±0.8 cm−1). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electricfield induced dissociation. By systematically varying the electric fields involved, and scanning the exciting photon energy, it was possible to determine the field-free energetic threshold for H35Cl+hν→H++35Cl−. Using this energy, together with the known values of the ionization potential of H and electron affinity of Cl, a new estimate for the dissociation energy of HCl was obtained: D0(H35Cl)=35 748.2±0.8 cm−1. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7205-7213 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of HI photodissociation following absorption in the A band (200 to 300 nm) was investigated by Doppler spectroscopy at the Lyman α transition of the H-atom photofragments. Measurements of both the branching ratios for the formation of spin-orbit excited I(2P1/2) and ground state I(2P3/2) atoms and the angular distributions of the recoil velocity for these two photofragment channels were obtained at nine photolysis wavelengths between 212.5 and 266 nm. These results show that ground state products result from a transition of perpendicular symmetry (ΔΩ=1), while the excited state atoms are produced from a parallel transition (ΔΩ=0). These experimental results, in combination with total absorption cross section data obtained prior to the present study, have enabled a calculation of the potential curves for the dissociative excited states. The outcome of the calculation was found to be in good qualitative agreement with the model of HI electronic structure originally suggested by Mulliken. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6658-6669 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photofragmentation dynamics of Fe(CO)5 in a supersonic molecular beam have been studied for photolysis wavelengths of 193, 248, 266, and 351 nm. The CO photofragments formed under these collision-free conditions were detected by vacuum ultraviolet laser-induced fluorescence (VUV LIF). This allowed for the determination of the rotational and vibrational distributions for the CO products and, by using Doppler spectroscopy, the translational energy distributions were also determined. These data are presented along with the details of a statistical model calculation which reproduces the experimental data very precisely. The statistical model for the photodissociation dynamics, which works at all photolysis wavelengths studied, is based on sequential elimination of CO ligands, with complete energy randomization in the intermediate ground state Fe(CO)n fragments between elimination steps. The detailed mechanism for the ultraviolet photochemistry of Fe(CO)5 is discussed in light of these results and previous experimental and theoretical work.
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