Browsing by Author "Cannon, Matt"
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Item Collisional formation of heavy Rydberg ion-pair states(2010) Cannon, Matt; Dunning, F. B.The formation of heavy Rydberg ion-pair states through electron transfer in collisions between K(np) Rydberg atoms and molecules that attach low-energy electrons is investigated. At low n, collisions with a wide variety of target species can lead to the formation of hound ion-pair states, a small fraction of which (under apropriate conditions) can subsequently dissociate as free ions through internal-to-translational energy transfer. The lifetimes of the ion-pair states can also be influenced by autodetachment of the electron or by neutralization through charge transfer. Two primary methods are employed to investigate the lifetimes of ion-pair states. Measurements of the onsets in the arrival time distribution of the ions provide lifetime information on short time scales (a few microseconds or less) for those ion pairs which undergo dissociation through conversion of internal energy. Additionally, ion pair behavior on longer time scales (> 1 --- 2 micros) can be studied as a function of binding energy through direct field dissociation.Item The effect of internal energy on the lifetime of sulfur hexafluoride negative ions(2007) Cannon, Matt; Dunning, F. B.The lifetimes of SF-6 ions produced in K(np)/SF6 collisions at high n are being investigated as a function of target temperature over the range 300K to 600K. At room temperature collisions are found to lead predominantly to the formation of long-lived SF-6 ions with lifetimes tau ≳ 1ms. As the target temperature is raised long-lived (tau ≳ 0.5ms) ions are still observed but their mean lifetime is reduced. In addition, the growth of a short-lived ion signal (tau ≳ 10 mus) is evident which, by 600K, accounts for ∼45% of the total SF-6 ion signal. These lifetimes are compared with those obtained using quasi-equilibrium theory and calculated SF-6 vibrational frequencies.