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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 411-419 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The joint product state distribution of coincident fragment pairs formed in the same elementary photodissociation process has been determined. This correlation between quantum state populations of two molecular products has been measured by high resolution Doppler spectroscopy in conjunction with level-specific detection of the ejected photofragments. One product molecule, formed in a specific quantum state, is excited by laser induced fluorescence and the wing of the corresponding Doppler profile is analyzed to determine the product state distribution of the partner fragment. In the photodissociation of jet-cooled hydrogen peroxide at 193 nm two OH partner radicals are formed with comparable angular momenta. For a specific rotation of one hydroxyl radical the product state distribution of the partner fragment is centered at about the same rotation with a width of only a few rotational quanta. The orbital angular momentum is of the order of 1 (h-dash-bar) and the impact parameter is extremely small. Experimentally observed joint product state distribution and trajectory calculations on ab initio potential energy surfaces are in excellent agreement.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6548-6555 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hydrazoic acid was excited to its lowest electronic excited state A˜ 1A‘ and the fragments were analyzed by high resolution Doppler spectroscopy. The NH fragment is rotationally cold, while N2 is strongly internally excited fint(N2)=0.48. The Λ doublets are populated statistically. The alignment of NH rotation vs the transition dipole moment of the parent is low (βμJ≤0.14). The vector correlation between the translational (vNH) and rotational (JNH) motion of the NH fragments is positive and increases with increasing JNH, indicating a preferential parallel alignment of vNH and JNH(βvJ(approximately-equal-to)0.40). The observed correlation between the transition dipole moment of the parent and the NH(1Δ) recoil velocity is negative at low NH rotations [βμv(JNH=2)=−0.4] and increases to positive values with increasing JNH. The HN3 distorts from a nonplanar configuration after excitation of a linear-bent electronic transition in the NNN framework, resulting in a strong N2 rotation and relatively weak NH rotation. The upper potential surface must be dependent on the torsional angle of the NN–NH system.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5709-5721 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the photodissociation of hydrogen peroxide has been analyzed by a complete characterization of the scalar and vectorial properties of the OH fragment using Doppler and polarization spectroscopy. When hydrogen peroxide is optically excited at 193 nm the hydroxyl radicals are formed exclusively in the X 2Π3/2,1/2 ground state with 84% of the available energy (Eav=417 kJ/mol) being released as OH recoil translation. The remaining energy is transferred in product rotation showing a strongly inverted rotational state distribution peaking at N‘=12. Vector correlations between the transition dipole moment of the parent H2O2 and the OH product rotational and translational motions were observed by Doppler broadened spectral lines and evaluated in terms of four bipolar moments. The quantitative contribution of two different electronic excited states in the dissociation process could be determined by analyzing the vector properties of the fragment. 62% of the OH products evolve from the A˜ 1A electronic excited state while 38% of the fragments are formed via the B˜ 1B state when hydrogen peroxide is excited at 193 nm. The OH rotational state distributions when produced from the A˜ 1A and the B˜ 1B state show no remarkable difference. The vector correlation of the recoil velocity vOH and the rotation JOH is strongly positive and increases with increasing JOH indicating a strong preference towards vOH and JOH being parallel to one another. The major part of product rotation is caused by a strong dependence on the torsion angle of the two upper potential surfaces.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 345-354 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formation of ground state OH(X) radicals from the photolysis of jet cooled H2O2 at 193 nm is studied by Doppler and polarization spectroscopy. The features of the process are characterized by a complete analysis of the scalar and vector properties of the fragments. In the dissociation process 85% of the available energy is released into fragment translation. The remaining part emerges as rotational excitation that performs a narrow Gaussian-like distribution peaking at N=12 with a FWHM of ΔN(approximately-equal-to)5. The vector correlations between the transition dipole moment μ of the H2O2 and recoil velocity v as well as angular momentum J of the products were evaluated in terms of four bipolar moments. The observed 〈μ ⋅ v〉 correlation was used to determine the state specific contribution of both the A˜ 1A and B˜ 1B dissociative states to the overall product rotational distribution. On the average, 65% of the OH fragments are formed via the 1A state. A comparison of data obtained from the photolysis of room temperature and jet cooled H2O2 molecules indicates that transfer of parent rotation causes a symmetric broadening of the product distribution and a small increase in the 〈v ⋅ J〉 correlation [βvJ(T(approximately-equal-to)20 K)=0.5, βvJ(T=300 K)=0.7] of the fragments. In order to describe the influence of initial parent motion on the product state distribution and on vector correlations a model is used where the formation of two OH radicals in the same microscopic event is considered.
    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 88 (1988), S. 6255-6259 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The correlation between angular momenta of the coincident product pairs formed in an elementary dissociation process has been investigated. Doppler shift measurements are used in connection with state-specific detection of scattered photofragments by laser-induced fluorescence. The method is demonstrated in the photodissociation of H2O2 and D2O2 at 193 and 266 nm where Doppler profiles of OH (OD) absorption lines are used to determine the (average) rotational energy of the OH (OD) partner molecule coincidently formed in the same elementary fragmentation process. At high product rotations the partner molecules are generated with comparable angular momenta, while at low rotational excitation a more complex correlation is observed. In addition to the partner fragment distribution, dissociation energies were determined to be 197 kJ/mol for HO–OH and 204 kJ/mol for DO–OD, which are significantly lower than the previously recommended values.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is proposed that the two Λ-doublet levels of linear molecules with nonzero electronic orbital angular momentum be labeled Λ(A') and Λ(A‘), e.g., Π(A') and Π(A‘) for Π states, etc., according to the following prescription: All series of levels in which the electronic wave function at high J is symmetric with reflection of the spatial coordinates of the electrons in the plane of rotation will be designated Λ(A') for all values of J, and all those for which the electronic wave function is antisymmetric with respect to reflection will be denoted Λ(A‘). It is emphasized that this notation is meant to supplement, and not replace, the accepted spectroscopic e/f labeling and the parity quantum number. The utility of the Λ(A')/Λ(A‘) notation is that it is of most relevance in the mechanistic interpretation of reactive or photodissociative processes involving open-shell molecules.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1988-1995 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the photofragmentation of hydroxylamine from its lowest excited electronic state, A˜ 1A', have been investigated. The main dissociation channel leads to H+H+HNO with a quantum efficiency of 1.7 for hydrogen atoms. The H atoms have been analyzed by laser induced fluorescence using a frequency tripled dye laser with sub-Doppler resolution. A sequential decay process is proposed where the first ejected H fragment leaves a highly vibrationally excited intermediate which dissociates after intramolecular vibrational redistribution into H+HNO. Another photodissociation channel leads to OH(X 2Π) and NH2(A˜ 2A1). NH2(A˜) has been detected by its emission spectrum, A˜ 2A1→X˜ 2B1, indicating strong vibrational excitation of the ν2 bending mode. The OH product shows no vibrational excitation, whereas rotational states up to N=20 have been observed. Observation of the product state distributions and of the 〈μ⋅v〉 and 〈v⋅J〉 correlations yield a qualitative picture of the upper potential energy surface (PES). Out of the nine coordinates characterizing the normal vibrational modes of H2NOH only the NO distance, the NOH bending angle (responsible for OH rotation), and the NH2 bending angle (responsible for NH2 bending motion) are involved in the NH2+OH fragmentation channel.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 3137-3143 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 1311-1315 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' journal of analytical chemistry 358 (1997), S. 335-338 
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Among the numerous techniques available for the characterization of diamond films scanning tunnelling microscopy (STM) in combination with spectroscopy (STS) provides information about the morphology and electronic surface properties down to the atomic scale. Here results of STM/STS obtained on diamond films are reported. 0.5 to 1.25 μm thick films have been grown on silicon substrates by hot filament chemical vapour deposition (HFCVD) by variable CH4/H2 mixtures in the range of 0.5% to 3% CH4. Morphological features of diamond crystallites were studied in detail by STM. A distinct increase of the surface roughness of (111) crystal faces with increasing CH4 concentration (from 0.5% to 3%) was found. For a CH4 concentration of 3% (100) faces were smoother than (111) faces. STS revealed significant differences in the tunneling current/voltage (I/V)-characteristics between (111) and (100) crystal surfaces. For (111) surfaces distinct changes in the I/V-characteristics depending on the CH4 concentration were observed: The I/V-characteristics change and the conductivity increases raising the CH4 concentration from 0.5% to 3%. This effect is explained with increasing formation of non-diamond carbon (NDC) on (111) surfaces for higher CH4 concentrations. Thus NDC is also responsible for the enhanced surface roughness observed on (111) surfaces with increasing CH4 concentrations.
    Type of Medium: Electronic Resource
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