Measured variation in the autoneutralization lifetime of SF−6 by direct measurement of neutral intensity

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Abstract
The autoneutralization lifetime of SF−6 has been studied by measuring the neutrals produced in a beam of SF−6 ions as a function of distance along the flight path. The measurement of neutrals (as opposed to ions) eliminated uncertainties encountered in previous investigators measurements. The beam was sharply focused, and the ion and neutral components were separated at various points along the flight path via electrostatic or magnetic fields. The neutral beam intensity was measured utilizing a multichannel plate array detector and photometer. The autoneutralization lifetime was measured as a function of pressure, acceleration voltage, and ion source temperature/photon flux. The effective lifetime increased from 15 to 20 μs as the ion source temperature/photon flux was reduced. Although the individual data sets exhibit a near single exponential behavior, composite analysis indicates multiple states (lifetimes) are active and that the process must involve a mixture of at least four states. The effect of temperature/photon flux on the effective single exponential lifetime implies that the distribution of energy states can be controlled to vary the composite autoneutralization rate.

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