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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Inorganic chemistry 27 (1988), S. 1209-1214 
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 105 (1983), S. 3738-3739 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 1208-1214 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 801-810 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared multiphoton dissociation (IRMPD) of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a molecular beam has been performed in order to investigate the mechanism of RDX thermal decomposition. A beam of molecules was crossed by a pulsed TEA CO2 laser and velocity distributions of the various products were measured by the time-of-flight (TOF) technique as a function of the laboratory angle using a mass spectrometric detector. The dissociation channels, their branching ratios, and the translational energy distributions of the products were determined. In contrast to the conventional view of simple bond rupture through loss of NO2 as the dominant primary channel in RDX decomposition, it was found that the dominant primary channel is concerted symmetric triple fission to produce three CH2N2O2 fragments which subsequently undergo secondary concerted dissociation to produce HCN, H2CO, HONO (or HNO2), and N2O. A total of two primary and four secondary dissociation channels were observed. Concerted reactions predominate over simple bond rupture not only in the number of channels (four vs two) but also in the amount of products. A fair amount of translational energy release through concerted reaction channels was observed, which is significant for an explanation of the energies of RDX decomposition.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2280-2286 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 2-Bromoethanol and 2-chloroethanol were photodissociated in a molecular beam at 193 nm. Only one primary reaction channel was observed, elimination of the halogen atom, with an average translational energy release of 33 kcal/mol. In the case of 2-bromoethanol, some of the C2 H4 OH partner fragment survived and some underwent secondary dissociation to produce C2 H4 and OH. The surviving C2 H4 OH contained up to 43 kcal/mol of internal energy, far more than the expected C2 H4 -OH bond energy of ∼28 kcal/mol. The initial C–Br recoil occurs with a large exit impact parameter and leaves most of the internal energy in C2 H4 OH rotation, creating rotationally metastable fragments. The angular distributions of the secondary C2 H4 and OH products were strongly forward–backward peaked with respect to the primary (C2 H4 OH) velocity vector, consistent with the decay of a long-lived complex in which the total angular momentum is perpendicular to the velocity vector and mainly carried away as orbital angular momentum. This effect is analogous to that observed in the decay of similar long-lived complexes in crossed molecular beam experiments.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4118-4127 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular-beam photofragmentation translational spectroscopy of cyclohexene and 1,4-cyclohexadiene was carried out using 193 nm and IR multiphoton excitation. At 193 nm, both the retro-Diels–Alder reaction of cyclohexene and H2 elimination from both molecules were observed in the ground electronic state, indicating the occurrence of internal conversion from the initially excited electronic states. The retro-Diels–Alder reaction is shown to be concerted up to an internal energy higher than 148 kcal/mol. Hydrogen-atom elimination was also observed for both molecules following 193 nm excitation. The H atom is eliminated from an excited state of cyclohexene and is assigned to be from a carbon adjacent to the double bond, with a corresponding C–H bond energy of 87±3 kcal/mol. It is shown that the peak of the translational energy distribution for concerted dissociation in the ground state is determined mainly by the dynamics of the potential-energy release along the reaction coordinate, and is not sensitive to either the amount of internal energy or the form of excitation.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5527-5535 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The method of photofragment-translational spectroscopy was used in a molecular beam study of the photochemistry of s-tetrazine. Following 1B3u ←1Ag (S1←S0 excitation) or 1B2u ←1Ag (248 nm excitation), s-tetrazine reverts to the highly vibrationally excited ground electronic state through internal conversion, then decomposes into 2HCN+N2 via concerted triple dissociation. By analyzing the experimental data with a simple model, it was found that the potential energy surface along the reaction coordinate after the transition state is very repulsive, leading to most of the available energy, on average 73.9% in the case of S1 ←S0 excitation, going into translation. The asymptotic angles between N2 and HCN with respect to the center of mass of s-tetrazine were 117.2±0.5° and 114.4±0.5° for S1 ←S0 and 248 nm excitation, respectively.
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  • 8
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Several studies have predicted substantial increases in Arctic ozone depletion due to the stratospheric cooling induced by increasing atmospheric CO2 concentrations. But climate change may additionally influence Arctic ozone depletion through changes in the water vapour cycle. Here ...
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 2799-2802 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9487-9495 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An optical–optical double resonance multiphoton ionization (OODR-MPI) technique has been developed for measuring the angular momentum reorientation in CO(A 1Π)–He inelastic thermal collisions. In this scheme, two-photon pumping of CO(A 1Π) by using a circularly polarized laser creates a highly anisotropic oriented angular momentum distribution in CO(A 1Π). A second counterpropagating circularly polarized laser probes the oriented CO(A 1Π) via 1+1 photon resonance ionization. A depolarization factor (D), which can be calculated from the measured intensity ratios between R and P branches in the OODR-MPI spectrum, is introduced to characterize the amount of collisional reorientation in the J→J' rotational energy transfer (RET). This method has the advantage of both high sensitivity and simplicity in data processing. The experimental results show the propensities that the depolarization factor D increases with ΔJ but decreases with increasing initial J. The D's are asymmetric with respect to ±ΔJ. For comparison, theoretical D's have been computed by an irreducible tensor formalism under the infinite-order-sudden approximation by Alexander and Davis [J. Chem. Phys. 78, 6754 (1983)] which is further simplified by using an exponential energy gap term to represent the dynamic effects. The computed curves of D vs ΔJ/J reproduce the experimental propensities. The best fit between theory and experiment is obtained with an average impact parameter b=2.9 A(ring), corresponding to a cross section of 26.4 A(ring)2, which is close to the experimental total cross section of CO(A 1Π)–He rotational energy transfer (∼28 A(ring)2).
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