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  • 1
    Electronic Resource
    Electronic Resource
    Differential cross sections for state-selected products by direct imaging: Ar+NO (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8618-8620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-selected differential cross sections have been obtained by directly imaging the products of collisions in crossed molecular beams. The new technique allows final state resolution and simultaneous detection of all scattering angles. The method has been used to study inelastic collisions between Ar and NO(2Π1/2, υ=0, J=0.5) at a collision energy of 0.21 eV. Rotational rainbows in the product angular distribution are directly observed to change in position as a function of the final rotational state; the peak of the angular distribution moves toward the backward hemisphere and the angular distribution broadens with an increase in final rotational quantum number. The method relies on multiphoton ionization of the product but is otherwise generally applicable to reactive as well as inelastic collisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462265
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  • 2
    Electronic Resource
    Electronic Resource
    State-resolved differential cross sections for crossed-beam argon-nitric oxide inelastic scattering by direct ion imaging (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 6342-6350 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100126a006
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  • 3
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of atomic carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2): Observation of diacetylene, C4H2(X 1Σg+) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8713-8716 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of ground-state carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2), is investigated at an average collision energy of 42.0 kJmol−1 employing the crossed molecular beams technique and a universal mass spectrometric detector. The laboratory angular distribution and time-of-flight spectra of the C4H2 product are recorded at m/e=50. Forward-convolution fitting of our data reveals the formation of diacetylene, HCCCCH, in its X1Σg+ electronic ground state. The reaction dynamics are governed by an initial attack of C(3Pj) to the π-electron density at the acetylenic carbon atom of the propargyl radical, followed by a [1,2]-hydrogen migration to the n-C4H3 isomer. A final carbon–hydrogen bond rupture yields atomic hydrogen and diacetylene through a tight exit transition state located 30–60 kJmol−1 above the products. This first successful crossed molecular beams study of a reaction between an atom and a free radical marks the beginning of the next generation of crossed beams experiments elucidating the formation of molecular species in combustion processes, chemical vapor deposition, in the interstellar medium, outflows of carbon stars, and hydrocarbon-rich planetary atmospheres via radical–radical reactions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475025
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  • 4
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of atomic carbon C(3Pj) with hydrogen sulfide, H2S(X1A1): Observation of the thioformyl radical, HCS(X2A′) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5288-5291 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One of the simplest organosulfur reactions, that between ground state carbon atoms, C(3Pj), and hydrogen sulfide, H2S(X1A1), was studied at an average collision energy of 21.0 kJ mol−1 using the crossed molecular beams technique. The product angular distribution and time-of-flight spectra of m/e=45 (HC32S) were monitored. Forward-convolution fitting of our data yields an almost isotropic center-of-mass angular flux-distribution, whereas the center-of-mass translational energy flux distribution peaks at about 50 kJ mol−1, indicating a tight exit transition state from the decomposing thiohydroxycarbene HCSH complex to the reaction products. The high energy cut-off of the translational energy flux distribution is consistent with the formation of the thioformyl radical HCS in its X2A electronic ground state. The first experimental verification of an existing thiohydroxycarbene intermediate and the rigorous assignment of the HCS radical product under single collision conditions explicitly suggest inclusion of the title reaction in chemical reaction networks of molecular clouds TMC-1 and OMC-1, the outflow of the carbon star IRC+10216, Shoemaker/Levy 9 impact-induced nonequilibrium sulfur chemistry in the Jovian atmosphere, as well as combustion of sulfur containing coal.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473561
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  • 5
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with hydrocarbon molecules. II. Chemical dynamics of n-C4H3 formation from reaction of C(3Pj) with methylacetylene, CH3CCH (X1A1) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8721-8733 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground-state carbon atoms, C(3Pj), and methylacetylene, CH3CCH (X1A1), was studied at average collision energies of 20.4 and 33.2 kJ mol−1 using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of C4H3 at m/e=51 were recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions isotropic at lower, but forward scattered with respect to the carbon beam at a higher collision energy. The translational energy flux distributions peak at 30–60 kJ mol−1 and show an average fractional translational energy release of 22%–30%. The maximum energy release as well as the angular distributions are consistent with the formation of the n-C4H3 radical in its electronic ground state. Reaction dynamics inferred from these distributions indicate that the carbon atom attacks the π-orbitals of the methylacetylene molecule via a loose, reactant like transition state located at the centrifugal barrier. The initially formed triplet 1-methylpropendiylidene complex rotates in a plane almost perpendicular to the total angular momentum vector around the B(backward-slash)C-axes and undergoes [2,3]-hydrogen migration to triplet 1-methylpropargylene. Within 1–2 ps, the complex decomposes via C–H bond cleavage to n-C4H3 and atomic hydrogen. The exit transition state is found to be tight and located at least 30–60 kJ mol−1 above the products. The explicit identification of the n-C4H3 radical under single collision conditions represents a further example of a carbon–hydrogen exchange in reactions of ground state carbon atoms with unsaturated hydrocarbons. This channel opens a versatile pathway to synthesize extremely reactive hydrocarbon radicals relevant to combustion processes as well as interstellar chemistry. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472677
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  • 6
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with hydrocarbon molecules. IV. Chemical dynamics of methylpropargyl radical formation, C4H5, from reaction of C(3Pj) with propylene, C3H6 (X 1A) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4945-4953 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state carbon atoms and propylene, C3H6, was studied at average collision energies of 23.3 and 45.0 kJ mol−1 using the crossed molecular beam technique. Product angular distributions and time-of-flight spectra of C4H5 at m/e=53 were recorded. Forward-convolution fitting of the data yields a maximum energy release as well as angular distributions consistent with the formation of methylpropargyl radicals. Reaction dynamics inferred from the experimental results suggest that the reaction proceeds on the lowest 3A surface via an initial addition of the carbon atom to the π-orbital to form a triplet methylcyclopropylidene collision complex followed by ring opening to triplet 1,2-butadiene. Within 0.3–0.6 ps, 1,2-butadiene decomposes through carbon–hydrogen bond rupture to atomic hydrogen and methylpropargyl radicals. The explicit identification of C4H5 under single collision conditions represents a further example of a carbon–hydrogen exchange in reactions of ground state carbon with unsaturated hydrocarbons. This versatile machine represents an alternative pathway to build up unsaturated hydrocarbon chains in combustion processes, chemical vapor deposition, and in the interstellar medium. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473543
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  • 7
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with hydrocarbon molecules. I. Chemical dynamics of the propargyl radical formation, C3H3 (X2B2), from reaction of C(3Pj) with ethylene, C2H4(X1Ag) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8705-8720 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground-state carbon atoms, C(3Pj), and ethylene, C2H4(X1Ag), was studied at average collision energies of 17.1 and 38.3 kJmol−1 using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of m/e=39 were recorded. Forward-convolution fitting of the results yields a maximum energy release as well as angular distributions consistent with the formation of the propargyl radical in its X2B2 state. Reaction dynamics inferred from the experimental data indicate two microchannels, both initiated by attack of the carbon atom to the π-orbital of the ethylene molecule via a loose, reactant like transition state located at the centrifugal barrier. Following Cs symmetry on the ground state 3A″ surface, the initially formed triplet cyclopropylidene complex rotates in a plane roughly perpendicular to the total angular momentum vector around its C-axis, undergoes ring opening to triplet allene, and decomposes via hydrogen emission through a tight transition state to the propargyl radical. The initial and final orbital angular momenta L and L′ are weakly coupled and result in an isotropic center-of-mass angular distribution. A second microchannel arises from A-like rotations of the cyclopropylidene complex, followed by ring opening and H-atom elimination. In this case, a strong L-L′ correlation leads to a forward-scattered center-of-mass angular distribution. The explicit identification of C3H3 under single collision conditions represents a single, one-step mechanism to build up hydrocarbon radicals. Our findings strongly demand incorporation of distinct product isomers of carbon atom-neutral reactions in reaction networks simulating chemistry in combustion processes, the interstellar medium, as well as in outflows of carbon stars, and open the search for the hitherto unobserved interstellar propargyl radical. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472652
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  • 8
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with hydrocarbon molecules. III: Chemical dynamics of propynylidyne (l-C3H;X 2Πj) and cyclopropynylidyne (c-C3H;X 2B2) formation from reaction of C(3Pj) with acetylene, C2H2(X 1Σg+) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1729-1741 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state carbon atoms, C(3Pj), and acetylene, C2H2(X 1Σg+), is studied at three collision energies between 8.8 and 45.0 kJ mol−1 using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of C3H at m/e=37 are recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions decreasingly forward scattered with respect to the carbon beam as the collision energy rises from 8.8 to 28.0 kJ mol−1, and isotropic at 45.0 kJ mol−1. Reaction dynamics inferred from the experimental data and ab initio calculations on the triplet C3H2 and doublet C3H potential energy surface suggest two microchannels initiated by addition of C(3Pj) either to one acetylenic carbon to form s-trans propenediylidene or to two carbon atoms to yield triplet cyclopropenylidene via loose transition states located at their centrifugal barriers. Propenediylidene rotates around its B/C axis and undergoes [2,3]-H-migration to propargylene, followed by C–H bond cleavage via a symmetric exit transition state to l-C3H(X 2Πj) and H. Direct stripping dynamics contribute to the forward-scattered second microchannel to form c-C3H(X 2B2) and H. This contribution is quenched with rising collision energy. The explicit identification of l-C3H(X 2Πj) and c-C3H(X 2B2) under single collision conditions represents a one-encounter mechanism to build up hydrocarbon radicals in the interstellar medium and resembles a more realistic synthetic route to interstellar C3H isomers than hitherto postulated ion–molecule reactions. Relative reaction cross sections to the linear versus cyclic isomer correlate with actual astronomical observations and explain a higher [c-C3H]/[l-C3H] ratio in the molecular cloud TMC-1 ((approximate)1) as compared to the circumstellar envelope surrounding the carbon star IRC+10216 ((approximate)0.2) via the atom-neutral reaction C(3Pj)+C2H2(X 1Σg+). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474092
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  • 9
    Electronic Resource
    Electronic Resource
    The dynamics of electronic to vibrational, rotational, and translational energy transfer in collision of Ba(1P1) with diatomic molecules (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4094-4103 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Doppler measurements taken over a range of probe-laser angles in a crossed-beam experiment were used, in conjunction with forward convolution analysis, to obtain flux–velocity contour maps for Ba(3P2) produced in a collision of Ba(1P1) with H2, N2, O2, and NO. The contour maps suggest a general model for the dynamics of this process in which large impact parameter collisions result in a near-resonant transfer of initial electronic energy into final vibrational energy, while close collisions produce sideways scattering and effectively couple electronic energy to translation. The molecular collision partners fall into two categories: for one group, comprising O2 and NO, the existence of a well-defined molecular anion with favorable Franck–Condon factors linking excited vibrational levels to the ground vibrational state of the neutral results in greatly enhanced coupling for the near-resonant process. Molecules for which there exist no stable anions, such as N2 and H2, represent a second category. The electronically inelastic collision for this group is instead dominated by the nonresonant process yielding the ground vibrational state and large translational energy release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463914
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  • 10
    Electronic Resource
    Electronic Resource
    A high-intensity, pulsed supersonic carbon source with C(3Pj) kinetic energies of 0.08–0.7 eV for crossed beam experiments (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 5405-5411 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An enhanced supersonic carbon source produces carbon atoms in their C(3Pj) electronic ground states via laser ablation of graphite at 266 nm. The 30 Hz (40±2) mJ output of a Nd-YAG laser is focused onto a rotating graphite rod with a 1000 mm focal length UV-grade fused silica plano-convex lens to a spot of (0.5±0.05) mm diameter. Ablated carbon atoms are subsequently seeded into helium or neon carrier gas yielding intensities up to 1013 C atoms cm−3 in the interaction region of a universal crossed beam apparatus. The greatly enhanced number density and duty cycle shift the limit of feasible crossed beam experiments down to rate constants as low as 10−11–10−12 cm3 s−1. Carbon beam velocities between 3300 and 1100 m s−1, with speed ratios ranging from 2.8 to 7.2, are continuously tunable on-line and in situ without changing carrier gases by varying the time delay between the laser pulse, the pulsed valve, and a chopper wheel located 40 mm after the laser ablation. Neither electronically excited carbon atoms nor ions could be detected within the error limits of a quadrupole-mass spectrometric detector. Carbon clusters are restricted to ∼10% C2 and C3 in helium, minimized by multiphoton dissociation, and eliminating the postablation nozzle region. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146061
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