Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 40-44 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photofragmentation of hydrogen peroxide has been investigated at an excitation wavelength of 266 nm using polarized laser beams. Doppler spectroscopy in connection with the laser induced fluorescence technique was applied to determine the nascent translational distribution of OH products. The hydroxyl radicals are formed in their electronic ground state, X 2Π3/2,1/2. The released energy is transformed almost exclusively in translation of these photoproducts. The Q1(4) transition in OH(X 2Π3/2→A 2Σ+) was used to study the anisotropic angular distribution of recoiling OH photofragments and analyzed to obtain information about the lifetime and symmetry of the excited dissociative state. The Doppler profiles for different directions of the electric field vectors of dissociation and probe laser relative to the detector axis have been determined for two different geometries. The angular distribution measured by Doppler spectroscopy, peaks in the direction perpendicular to the electric vector of the dissociating laser light, indicating that the predominant electronic excited state in H2O2 must be of 1A symmetry. An upper limit for the lifetime τ of the excited H2O2 parent molecule before dissociation is τ≤6×10−14 s.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 0570-0833
    Keywords: Dynamics ; Photochemistry ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photofragmentation - also termed ‘half collision’ - is a method to comprehend the complicated process of a chemical reaction (the ‘full collision’) better. The use of polarized light enabled the study of the spectroscopy of aligned molecules, yielding information about the photochemically produced intermediate state - the transition state. Even though stable reaction products were studied, the forces responsible for the motions of the fragments can be visualized. In this way a model can be constructed that represents the part of the potential hypersurface responsible for the observed motions. The application of this spectroscopic method to hydrogen peroxide H2O2 has become a classic example. The complex decomposition of hydrazoic acid, HN3, represented a challenge, and its successful solution proves the general applicability of this method.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Photofragmentierung - sie wird auch Halbstoß genannt - ist ein Weg, den komplizierten Prozeß einer chemischen Reaktion - den Ganzstoß - besser zu verstehen. Durch die Verwendung von polarisiertem Licht wird eine Spektroskopie an ausgerichteten Molekülen möglich, und dadurch werden Informationen über den photochemisch erzeugten Zwischenzustand - den Übergangszustand - zugänglich. Obwohl die stabilen Endprodukte untersucht werden, können die Kräfte sichtbar gemacht werden, die für die Bewegung der Fragmente ursächlich sind. Daraus läßt sich ein Bild von dem Teil der Potentialhyperfläche gewinnen, auf dem die beobachtete Bewegung abläuft. Die Anwendungen dieser spektroskopischen Methode auf das Wasserstoffperoxid H2O2 sind schon zum Schulbeispiel geworden. Der komplexe Zerfall der Stickstoffwasserstoffsäure HN3 war eine Herausforderung an die Methode. Seine gelungene Analyse beweist ihre Aussagekraft.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In der Troposphäre, dem der Erdoberfläche zugewandten unteren Teil der Erdatmosphäre, spielen sich unsere Lebensvorgänge ab. Dieser wichtige Teil unserer Umwelt besteht zur Hauptsache aus Stickstoff und Sauerstoff. Daneben enthält er eine Reihe anderer Stoffe, die aber weitgehend in geringer Konzentration auftreten und Spurenstoffe genannt werden. Daß der Gehalt an diesen Stoffen so gering ist, geht hauptsächlich auf die Aktivität eines zweiatomigen Radikals, des Hydroxylradikals, zurück. OH steuert den Hauptteil zum oxidativen Potential der Troposphäre bei und überführt viele Spurenstoffe in wasserlösliche Formen, die dann durch Ausregnung aus der Troposphäre entfernt werden können. Es hat sich deshalb auch der Name “Waschmittel der Atmosphäre” für das OH-Radikal eingebürgert. Die Kenntnis seiner räumlichen Konzentration ist eine wichtige Information, vor allem auch im Hinblick auf atmosphärenchemische Modellrechnungen. Diese Konzentration, die sehr niedrig ist und deren experimentelle Bestimmung analytisch enorm anspruchsvoll ist, wird empfindlich durch chemische Auf- und Abbaureaktionen bestimmt, die zusammenwirkend einen Recyclingprozeß in der Troposphäre verursachen.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 0570-0833
    Keywords: Atmospheric chemistry ; Hydroxyl radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The troposphere, the part of the earth's atmosphere which is closest to the surface, harbors important life processes. This important part of our environment contains primarily nitrogen and oxygen. In addition, it comprises a number of other substances, which are generally present in low concentrations. The primary reason for the low content of these trace components is the activity of a diatomic radical, namely the hydroxyl radical. OH is the main constituent of the oxidizing potential of the troposphere and causes the transformation of many trace components into water-soluble forms, which can then rain out and be removed from the troposphere. OH has therefore acquired the title “detergent of the atmosphere”. The knowledge of local hydroxyl radical concentrations is therefore an important piece of information, especially with respect to model calculations for atmospheric chemistry. The OH concentration is very low and its determination represents a significant analytical challenge. It is controlled in a delicate manner by chemical formation and decomposition reactions, which interact to create a recycling process in the troposphere.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The influence of the electronic asymmetry in the 1Δ(A') and 1Δ(A‘) Λ doublets of NR (R=H,D) on the photodissociation dynamics of hydrazoic acid (RN3) has been investigated. Hydrazoic acid was prepared in its first excited electronic state, A˜1A‘. A variety of scalar (internal state and translational energy distribution) and vectorial (angular distribution, rotational alignment, correlation between translational and rotational motion) properties of the ejected NH or ND fragment were analyzed by Λ-doublet-specific Doppler profile measurements. While the population of the 1Δ(A') and 1Δ(A‘) states are equal, the vector correlations for both Λ sublevels are different. NR(A‘) products are preferentially ejected in the original plane formed by the parent, and the recoil of NR fragments in the symmetric Δ(A') state is preferentially perpendicular to that plane. The vector correlation between the translational and the rotational motion of the fragment also indicates a strong nonplanar dissociation geometry for NR products in the Δ(A') state. About 50% of the ND(A') product rotation is generated by a torsional motion, while 80% of the ND(A‘) fragments are formed with J being aligned perpendicular to the recoil direction (MJ=0).
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hydrogen peroxide has been optically excited at a wavelength of 266 nm and the OH photofragment completely characterized by Doppler and polarization spectroscopy using the laser-induced fluorescence technique. The entire internal state distribution (vibration, rotation, spin, and Λ components), translational energy, angular distribution, rotational alignment, and vector correlations between rotational and translation motions of OH products is measured. The hydroxyl radicals are formed in the X 2Π3/2,1/2 ground state with 90% of the available energy (248 kJ/mol) being released as OH recoil translation. The angular distribution is nearly a sin2 θ distribution about the electric vector of the photolysis laser. The internal motion of OH is vibrationally cold (no vibrationally excited OH was found) while the rotational excitation in v‘=0 can be described by a Boltzmann distribution with a temperature parameter of Trot=(1530±150) K. The two spin states are found to be populated nearly statistically, in contrast to the Λ components which show an increasing inversion with increasing OH rotation. The observed profiles of recoil Doppler broadened spectral lines are strongly dependent on the nature of the transition, the excitation–detection geometry, and the relative polarizations of the dissociating and analyzing laser light. However, the line intensities show only a minor dependence on geometry and polarization indicating a low alignment of OH photofragments (A(2)0≤0.1). For the first time the vector correlation between product rotational and translational motions was analyzed and evaluated in terms of the three bipolar moments β20(20), β00(22), and β20 (22). The bipolar moment β20(20) corresponds to the conventionally defined anisotropy parameter β=2β20(20) =−0.71. The angular distribution peaks in the direction perpendicular to the electric vector of the dissociating laser light, indicating the predominant electronic excited state in H2O2 being of 1A symmetry. The moment β00(22) increaseswith JOH showing a bias towards vOH and JOH being parallel to one another. The moment β20(22) is a measure of the mutual correlation of the fragment translational and rotational vectors and the transition dipole vector μ in the parent molecule. The positive value of this moment [β20(22)=0.11] indicates that the expectation value of 〈J2y〉 should be very small when μ is parallel to the z axis and vOH perpendicular to μ (x axis). 〈J2x〉 originates in the torsional motion in the H2O2 parent molecule, while 〈J2z〉 reflects the bending vibration of nearly planar H2O2 where the H atoms are in the trans position.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3238-3247 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultraviolet photodissociation of phosgene in its first absorption band 1A2←1A1 was investigated by resonance enhanced multiphoton ionization and time of flight techniques. Nascent atomic chlorine fragments were observed and their state specific kinetic energy distributions were determined. Of the chlorine atoms 15% are produced in the excited 2P1/2 spin–orbit state with a mean kinetic energy of 3200 cm−1 compared to a value of 1500 cm−1 for the mean kinetic energy of the ground state chlorine atoms. The analysis of the kinetic energy spectra yielded evidence for a concerted three-body decay. The formation of intermediate COCl is of minor importance in the dissociation process, the formation of a stable final COCl product can be excluded. Competing pathways on the upper potential energy surface are discussed. A significant excitation of the carbon monoxide CO fragments is predicted. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...