Abstract by Brandon Turner
Chemistry and Biochemistry
Daniel Austin, Eric Sevy
High Velocity Impact Fragmentation Pathways of Neutral Molecules in Flyby and Orbiter Mass Spectrometers
The Ion and Neutral Mass Spectrometer (INMS) onboard Cassini was used to characterize molecules in tenuous atmospheres. Neutrals enter this source with high relative velocities and are subsequently thermalized through collisions with the chamber walls. The speed of thermalization depends on the number of collisions with the chamber walls and the rate at which these collisions take place. Such collisions with the chamber walls cause vibrational excitation of the neutrals and can have enough energy to cause a chemical change in the molecule unless another collision occurs before the molecule can dissociate. Calculations to determine the dissociative lifetimes of neutral molecules are being performed and assume a 15% translational-to-vibrational energy transfer upon impact. Once the dissociative lifetimes are calculated, they are compared to the time between successive collisions to determine if there is enough time for the molecule to thermalize or if it will dissociate before entry into the ionization region of a mass analyzer. The extent of fragmentation depends on the amount of time the molecule spends in a state of high vibrational energy.