Clustering of Ar toLi+and a Comparison of Drift-Tube Models

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Abstract
The clustering of Ar to Li+ has been studied experimentally using a drift tube. The measurements were made at a gas temperature of 319 °K. The gas pressure was varied between 0.5 and 1.5 Torr, and EN was varied between 9 and 24 Td (1 Td = 10−17 V cm2). Under these conditions, the major reaction is Li++Ar+Ar⇄Li+(Ar)+Ar. The rate coefficients and the mobility of Li+(Ar) were deduced by comparing measured arrival-time profiles of the ions with profiles generated by a three-dimensional, numerical drift-tube model. The predictions of this model are compared in some detail with those of two analytical, three-dimensional, drift-tube models. In all cases the agreement is satisfactory. We find that the association-rate coefficient k1 is 1.8 × 10−31 cm6/sec and remains constant over the range of EN used and that the collisional-dissociation-rate coeffiecient k−1 increases from 2.0 × 10−13 cm3/sec at EN=9 Tdto 3.2×10−13 cm3/sec at EN=24 Td. In addition, we find the reduced mobility of Li+(Ar) in Ar to be 2.0 cm2/V sec, measured at 319 °K. The amounts by which these values may be in error were determined as ± 24% for the association-rate coefficients, ± 22% for the collisional-dissociation-rate coefficients, and ± 16% for the mobility of Li+(Ar). The mobilities of K+ in N2 and of K+ in Ar were determined during checks for systematic errors in the new drift tube. The mobility of Li+ in Ar was also determined in the course of this work. Both random and systematic errors were considered in the determination of the standard deviations of these measurements. These reduced mobilities and their standard deviations are: K+ in

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