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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6418-6425 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ∼235 nm photodissociation of CH3CFCl2 pre-excited to three, four, and five quanta of C–H methyl stretches was studied to investigate the effect of internal parent excitation on the dynamics of two- and three-body photofragmentation. The ∼235 nm photons also tagged spin-orbit ground Cl 2P3/2 [Cl] and excited Cl 2P1/2 [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer. Monitoring the shapes of 35Cl and 35Cl* time-of-arrival profiles revealed their energies and angular distributions and showed broad and unstructured fragment kinetic energy distributions. Although a significant amount (∼50%) of the available energy is transferred into internal energy of the CH3CFCl fragment, the spatial Cl distribution is characterized by a nonvanishing anisotropy parameter, β, which indicates at a fast dissociation of the parent molecule along the C–Cl dissociation coordinate. Moreover, β for Cl changes from a slightly positive value to a negative value, while that for Cl* increases when the pre-excitation is increased from three to five quanta of C–H methyl stretches. This is attributed to the promotion of one of the nonbonding electrons located on the Cl atoms to the σ* antibonding C–Cl orbital and involvement of several upper states with different symmetry properties. © 2001 American Institute of Physics.
    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 117 (2002), S. 2141-2150 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-resolved and isotope-specific detection of nascent ClO generated from the photodissociation of Cl2O parent molecules is performed by observing single-color (2+1) resonance enhanced multiphoton ionization (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm; additionally state-resolved detection of nascent ClO is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C 2Σ−,v′=0←X 2ΠΩ,v=0) transition. The population of rotational states up to J=130 is evidence of large rotational excitation induced by a strong dependence of the excited potential energy surface (PES) on the Jacobi angle γ. Formation of the 2Π3/2 spin-orbit state is preferred: P(2Π1/2):P(2Π3/2)=0.30±0.05 suggesting significant radiationless transfer from the excited PES to closely lying neighboring states. The anisotropy parameter for the transition is determined to be β=0.35 independent of the ClO quantum state. The principal excited electronic state is assigned to a 1B2←1A1 transition, in agreement with recent ab initio calculations. The measured β value is smaller than the limiting value of 1.0, suggesting dynamic reasons and simultaneous excitation to more than one PES. A fast and direct fragmentation process is deduced, where the upper limit for the lifetime of the excited dissociative state is calculated to be 300 fs. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of thiophosgene (CSCl2) and the respective branching ratios of both dissociation products Cl and CSCl have been studied by 3D imaging of the photodissociation product chlorine in its ground state 2P3/2[Cl] and excited spin–orbit state 2P1/2[Cl*] employing the resonance enhanced multiphoton ionization and time-of-flight technique at a dissociation wavelength of about 235 nm. A novel technique is applied where the complete three-dimensional (3D) momentum vector of a reaction product is directly determined. The kinetic energy distribution (KED) for Cl* is observed for the first time. The obtained KEDs of Cl and Cl* are different in the low kinetic energy range due to the correlating state of the partner fragment CSCl. In the case of ground state Cl the CSCl partner radical is produced in the ground X˜, A˜, and B˜ states with a contribution of 4±0.5%, 60±5%, and 36±3%, respectively. In the case of Cl* the corresponding CSCl is produced with a contribution of 7.5±0.5% in the ground X˜, 71.5±5.5% in state A˜, and 21±1.5% in state B˜. The yield of Cl*, φ(Cl*)=P(Cl*)/[P(Cl)+P(Cl*)], was found to be 0.47. No significant velocity dependence of the anisotropy parameter β could be observed. The mean value +0.03 suggests a decay on the B˜ (A1) surface. © 2002 American Institute of Physics.
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of COCl2 has been studied by monitoring ground Cl(2P3/2) and spin–orbit excited Cl*(2P1/2) fragments by applying a novel technique where the three-dimensional momentum vector of a single reaction product is directly determined. The photodissociation at 235 nm produces exclusively three fragments: COCl2+hν→CO+2Cl. The kinetic energy distributions of Cl and Cl* are bimodal and exhibit a different behavior for the different spin–orbit states. Our attention was turned to the dependence of the anisotropy parameter β on the fragment velocity which was observed for the first time. For both spin–orbit states the anisotropy parameter differs clearly for slow and fast chlorine atoms, where a pronounced change from the value ∼0.7 to zero at about 20 kJ/mol is observed. Slow chlorine atoms are released isotropically and predominantly in the ground state Cl whereas fast chlorine atoms have an anisotropy parameter close to the theoretically limiting value and are distributed between ground and excited state Cl. These observations can be explained by a sequential decay where the first Cl fragment is released in a fast process characterized by the nonvanishing positive β parameter and a lifetime of ≤210 fs, whereas the second Cl fragment is released after a period which is long on a rotational time scale. A significant contribution of a symmetric mechanism can be excluded. © 2002 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10582-10591 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of OClO in the near ultraviolet (UV) was investigated in a state specific and energy selective manner. At a dissociation wavelength of 308 nm, OClO(X˜ 2B1) was excited to the OClO(A˜ 2A2(18,0,0)) state, from which it decays into ClO(X 2Π3/2,1/2) and O(3P2,1,0). The nascent oxygen fragments were detected spin selectively by resonant enhanced multiphoton ionization and time of flight measurements (REMPI-TOF). Based on the measurements and the conservation of energy and linear momentum, the internal energy of the ClO partner fragment was obtained. On average, more than 60% of the available energy is transferred into internal excitation of the ClO radical. Nearly the whole internal energy is vibrational energy with vibrational levels populated up to the energetic limit. Besides, the internal energy depends on the oxygen spin-orbit state because the fraction of highly excited ClO fragments increases with increasing total angular momentum J. The bimodal behavior of the fragment energy distribution indicates two different dissociation pathways, in which one leads to ClO radicals excited up to v=10 and the other one up to v=15. Furthermore, the decay is anisotropic, which was proved by polarization experiments. This is a hint for a short decay time estimated to be in the order of a few hundred femtoseconds. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    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
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