ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
The near ultraviolet (UV) and visible photodissociation dynamics of BrCl have been explored using the technique of photofragment ion imaging at 26 wavelengths in the range 235 to 540 nm. Ion images of the Cl(2P3/2), Cl(2P1/2), Br(2P3/2) and Br(2P1/2) photofragments reveal both the angular distributions of photofragment velocities (characterized by anisotropy parameters, β) and which of the four possible photofragment pathways are active at different wavelengths. The anisotropy parameters show extensive variation both with wavelength and for the different fragmentation channels, and these variations are interpreted largely in terms of excitations to the A 3Π(1), B 3Π(0+), C 1Π(1) and D(0+) states as the wavelength is reduced. At wavelengths between 235 and 262 nm, the Br(2P1/2)+Cl(2P3/2) channel is dominant and β=2.0±0.1 at 235 nm, characteristic of a parallel parent transition (ΔΩ=0) and supporting previous assignments of the absorption in this wavelength range being due to the D(0+)–X 1Σ+(0+) transition. A minor channel forms Cl(2P1/2)+Br(2P3/2) with an anisotropy indicative of the involvement of an underlying perpendicular absorption (ΔΩ=±1) to a state with Ω=1. Br(2P3/2)+Cl(2P3/2) and Br(2P1/2)+Cl(2P1/2) fragmentation channels are not observed. Excitation in the wavelength range 320 nm to 410 nm results in Cl(2P3/2)+Br(2P3/2) products with an anisotropy parameter of β=−1.0±0.1, consistent with assignment of the strong parent absorption to the C 1Π(1)–X 1Σ+(0+) transition. For photolysis wavelengths longer than 400 nm, the Cl(2P1/2)/Cl(2P3/2) branching ratio increases [with β∼1.0 to 1.4 for the Cl(2P1/2)], β for Cl(2P3/2) becomes less negative (and for λ≥450 nm, values lie in the range 0 to −0.2) and Br(2P3/2) β-parameters also increase. No formation of Br(2P1/2) is observed. These observations are, in part, consistent with absorption via the B 3Π(0+)–X 1Σ+(0+) transition, although the nonlimiting β-parameter values imply a significant perpendicular contribution to the absorption spectrum. The measured anisotropy parameters for λ≥410 nm are interpreted in terms of excitation both to an Ω=0 state [B 3Π(0+)] and an Ω=1 state [A 3Π(1) or C 1Π(1)], together with transfer of dissociating flux between states during the dissociation. © 1998 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.477039
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