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W. M. Jackson, D. Xu, J. Huang (University of California, Davis)
The velocity distribution of daughter products produced by photodissociation is an important parameter for determining their progenitors. Spatial profiles of cometary emissions are usually analyzed with the Haser or the Festou vector models, which gives a parameter called the scale length, \gamma. The scale length is defined as the product of the velocity of the species in the comet, u, times the photochemical lifetime, \tau. This later quantity is the inverse of the integral over all solar wavelengths of the absorption coefficient of the parent times the solar flux. The parent of the fragments can be determined from the photochemical lifetime if the recoil velocity,v,is known. This recoil velocity can then be combined with the gas flow velocity to determine the cometary velocity of the species.
A pulsed supersonic molecular beam apparatus combined with a velocity ion imaging is used to determine the identity and velocity distributions of the daughters produced by photodissociation. The CS2 is studied in its primary photodissociation regime between 193- 202 nm that produces sulfur atoms in the 3P and 1D electronic states. The recoil velocity and branching ratios of the two different states of the sulfur atom atoms that are produced has been determined. Combining this information with the solar photochemical rate constants for this wavelength region allow us to determine an average recoil velocity for cometary sulfur atoms produced by solar photolysis of cometary CS2. The implication of these results will be discussed.
This work was supported by the Chemistry Division of the National Science Foundation (NSF) (Grant No. CHE-0100965) and the Planetary Atmosphere program NASA (Grant No. NAG5-12124).
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.