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  • 1
    Electronic Resource
    Electronic Resource
    Correlated photochemistry: the legacy of Johann Christian Doppler (1989)
    s.l. : American Chemical Society
    Accounts of chemical research 22 (1989), S. 309-314 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00165a003
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  • 2
    Electronic Resource
    Electronic Resource
    The 157 nm photodissociation of OCS (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5364-5372 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of OCS at 157 nm has been investigated by using tunable vacuum ultraviolet radiation to probe the CO and S photoproducts. Sulfur is produced almost entirely in the 1S state, while CO is produced in its ground electronic state and in vibrational levels from v=0–3 in the approximate ratio (v=0):(v=1):(v=2):(v=3)=(1.0):(1.0):(0.5) :(0.3). The rotational distribution for each vibrational level is found to be near Boltzmann, with temperatures that decrease from 1350 K for v=0 to 780 K for v=3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from a transition of predominantly parallel character (β=1.8±0.2) and that the CO velocity and angular momentum vectors are perpendicular to one another.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456443
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  • 3
    Electronic Resource
    Electronic Resource
    Competition between direct-inelastic and trapping desorption channels in the scattering of NO (v=0, J) from Ir(111) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6548-6555 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The competition between direct-inelastic and trapping-desorption scattering of NO from IR(111) has been studied using multiphoton ionization and time-of-flight mass spectrometry. Molecules interacting by each mechanism were observed and characterized by their angular, velocity, and internal state distributions. For Ts〈300 K both channels are observed, while for Ts〉300 K only trapping-desorption is observed. At Ts〈300 K, the trapping fraction was (approximately-equal-to)0.85. The shift in scattering mechanism appears to be caused by a change in the surface composition due to dissociation of chemisorbed NO near room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454441
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  • 4
    Electronic Resource
    Electronic Resource
    State-to-state photodissociation dynamics of trans-glyoxal (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1258-1268 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.452215
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of carbon dioxide at LiF(100) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5661-5676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation of CO2 at LiF(100) has been investigated by monitoring infrared fluorescence from vibrationally excited molecules under conditions where they are relaxed primarily by collisions with the solid surface. The relaxation probabilities are found to be 0.65±0.10 at room temperature and 0.35±0.10 at 450 K. In order to understand better the vibrational relaxation results, angular distributions of CO2 scattered from LiF(100) were measured with a molecular beam scattering apparatus. At slow incident beam velocities, the trapping probability of CO2 at LiF(100) is essentially unity. Thus, in the vibrational relaxation measurements, where the incident velocity is even slower than in the scattering experiments, vibrational relaxation is preceded by trapping. Possible mechanisms for relaxation are discussed. Excitation of phonons in the solid and transfer of energy to other degrees of freedom of the molecule (i.e., translation, rotation, and other vibrational modes) are both plausible relaxation channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458498
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  • 6
    Electronic Resource
    Electronic Resource
    Methyl rotation, vibration, and alignment from a multiphoton ionization study of the 266 nm photodissociation of methyl iodide (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4222-4236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of CH3I and CD3I have been examined by using multiphoton ionization to probe the CH3, CD3, I(≡5 2P3/2) and I*(≡I 5 2P1/2) photoproducts. The parent compounds were cooled in a supersonic expansion, collimated into a molecular beam, and dissociated at 266 nm. For the CD3I dissociation, the ratio of CD3(v=0)/(v=2) was estimated to be about 1.1, with multiple determinations ranging from 0.47–2.1. The quantum number v here denotes the nascent excitation of the ν2 "umbrella'' mode. Measurements of the CD3(v=1) and (v=3) vibronic bands indicated that the (v=1)/(v=3) ratio is greater than unity, with some measurements suggesting values as large as 10. A value for the CH3(v=0)/(v=2) ratio from dissociation of CH3I could not be estimated, although it was clearly larger than that for CD3. The CH3(v=0) and CD3(v=0) products from this dissociation are fit by 120±30 K and 105±30 K rotational distributions, respectively. The dissociation mechanism produces alignment in the molecular frame such that there is a strong preference for K=0 (rotation perpendicular to the top axis). Assuming that the relative velocity vector lies along the CH3 C3 axis, the velocity and rotation vectors tend to be perpendicular. It is likely that K=0 molecular frame alignment is produced in photodissociation through both the I and I* channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455779
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  • 7
    Electronic Resource
    Electronic Resource
    State-selective studies of T→R, V energy transfer: The H+CO system (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5481-5488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional energy transfer from H atoms to CO(v=0, J(approximately-equal-to)2) has been studied at a collision energy of 1.58±0.07 eV by photolyzing H2S at 222 nm in a nozzle expansion with CO and probing the CO(v‘, J‘) levels using tunable VUV laser-induced fluorescence. The ratio CO(v‘=1)/CO(v‘=0) is found to be 0.1±0.008. The rotational distribution of CO(v‘=0) peaks at J‘≤11 and decays gradually; population is still observed at J‘≥45. The rotational distribution of CO(v‘=1) is broad and peaks near J‘=20. The experimental results are compared to quasiclassical trajectory calculations performed both on the H+CO surface of Bowman, Bittman, and Harding (BBH) and on the surface of Murrell and Rodriguez (MR). The experimental rotational distributions, particularly those for CO(v‘=1), show that the BBH surface is a better model than the MR surface. The most significant difference between the two surfaces appears to be that for energetically accessible regions of configuration space the derivative of the potential with respect to the CO distance is appreciable only in the HCO valley for the BBH surface, but is large for all H atom approaches in the MR potential. Because the H–CO geometry is bent in this valley, vibrational excitation on the BBH surface is accompanied by appreciable rotational excitation, as observed experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454559
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  • 8
    Electronic Resource
    Electronic Resource
    Angular correlations between recoil velocity and angular momentum vectors in molecular photodissociation (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3682-3691 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A technique has been developed for determining the angular correlation between a photofragment's angular momentum vector J, its recoil velocity vector v, and the transition dipole moment of the parent molecule μp . Doppler profile spectroscopy used in conjunction with laser-induced fluorescence probing by polarized light can be used to determine the correlations. The pairwise correlations between these vectors as well as their triple correlation are discussed for limiting cases using a classical approach as well as for the general case using a quantum approach based on density matrices. The current formulations differ in two ways from the recent approach of Dixon, who used a bipolar expansion of the correlated velocity and angular momentum distributions. The physical basis for the influence of the vector correlations on the Doppler profile is somewhat more transparent in the current formulations, and the direct connection between the measured correlations and the t-matrix elements occurring in the theory of Balint-Kurti and Shapiro for the photodissociation of a triatomic molecule is also demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453868
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  • 9
    Electronic Resource
    Electronic Resource
    State-resolved photodissociation of OCS monomers and clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3692-3708 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453869
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  • 10
    Electronic Resource
    Electronic Resource
    Dissociation dynamics of C3O2 excited at 157.6 nm (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1837-1849 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation of carbon suboxide by single photon absorption at 157.6 nm has been studied under the collisionless environment of a molecular beam. The primary products are 2CO+C [3P(97%) or 1D(3%) ]. The spin–orbit levels of the 3P carbon are statistically distributed. The CO rotational populations in the first four vibrational levels are found to be well described by Boltzmann distributions with temperatures 3430, 4120, 4670, and 2340 K for υ=0,1,2,3, respectively. A second low temperature component in the υ=0 rotational distribution is attributed to CO produced in coincidence with C(1D). Significant population is found in the first four vibrational levels with less than 3% estimated in the higher levels; a vibrational temperature of 3700 K fits the distribution. Analysis of the Doppler profiles of the CO and carbon suggest that the dissociation is stepwise; the first dissociation appears to be described by an anisotropy parameter near β=2, while the second appears to be isotropic. The mean CO fragment speeds were nearly constant for all rotational levels, though slightly faster for υ=1 than υ=0. From the translational energetics of the CO at least a small amount of stable C2O is inferred to exist. The overall energetics place the stable C2O quantum yield under 2% assuming that excited C2O is not radiatively stabilized. We were unable to detect C2O directly in any electronic state. The dissociation of C3O2 into C(3P)+2CO appears to be best described as a stepwise reaction that produces a nearly statistical partitioning into all fragment degrees of freedom. The best agreement is obtained for an intermediate C2O electronic state in the vicinity of the b˜ state (e.g., b˜, a˜ or A˜); a ground state C2O intermediate is unlikely. The singlet to triplet crossing most likely occurs in the C2O system on a time scale longer than a rotation (a few picoseconds).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459958
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