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MO: Molekülphysik
MO 23: Photochemistry
MO 23.4: Vortrag
Dienstag, 14. März 2006, 14:45–15:00, H12
Are branching ratios in the photodissociation of CCl4 isotope specific? — •Christof Maul — Institut für Physikalische und Theoretische Chemie, TU Braunschweig, 38106 Braunschweig, Germany
Photodissociation of CCl4 in the ultraviolet produces chlorine atoms in their ground [Cl(2P3/2)] and excited spin-orbit [Cl*(2P1/2)] states. In 1994, Deshmukh and Hess, reported isotope specific relative yields φ in the photodissociation of CCl4 where φ is defined as the percentage of Cl atoms in a given spin-orbit state. In particular, φ(35Cl*) was reported to be 0.20 while φ(37Cl*) was found to be 0.44. The data were obtained from integrated intensities of line profiles monitored for Cl/Cl* detection by (2+1) resonance enhanced multiphoton ionization (REMPI) where 35Cl and 37Cl isotopes were separated in a time-of-flight spectrometer. No explanation was given for the alleged phenomenon.
In order to verify the observation of isotope specific branching ratioes the CCl4 photodissociation was reinvestigated. Instead of comparing integrated line intensities for different electronic transitions of one selected isotope, the isotopic distribution for five carefully chosen electronic transitions was monitored. Thus, the laser intensity could be adjusted to signal intensity, and changes in laser intensity affected both isotopes in the same way. For all transitions the observed isotopic fragment distribution was found to be equal to the natural distribution within experimental error. Thus, it must be concluded that branching ratios in the photodissociation of CCl4 are not isotope specific.