Single and double clustering of nitrogen to Li⁺

The clustering of N₂ to Li⁺ has been studied experimentally using a drift tube at a gas temperature of 318K. The gas pressure was varied between 0.5 and 1.5 Torr, and E/N (the ratio of the uniform electric field strength in the drift region to the neutral number density) was varied between 9 and 24 Td (1 Td=10^-17 V cm²). Under these conditions, the major reactions are Li⁺+N₂+N₂⇄k₂₁k₁₂Li⁺·N₂+N₂ and Li⁺·N₂+N₂+N₂⇄k₃₂k₂₃Li⁺2N₂+N₂ The rate coefficients and the mobilities of Li⁺·N₂ and Li⁺·2N₂ were deduced by comparing measured arrival-time profiles of the ions with profiles generated by an analytical drift-tube model developed for three interreacting ion swarms. We find that the association rate coefficient k₂₁ decreases from 2.0×10^-30 cm⁶/sec at E/N=9 Td to  1.7×10^-30 cm⁶/sec at E/N=24 Td, the collisional-dissociation rate coefficient k₁₂ increases from 0.7×10^-14 cm³/sec at E/N=9 Td to 1.6×10^-14 cm³/sec at E/N=24 Td, and the collisional-dissociation rate coefficient k₂₃ increases from 4.8×10^-13 cm³/sec at E/N=9 Td to  1.6×10^-14 cm³/sec at E/N=24 Td. Adequate fits could be obtained with values of k₃₂ from 1.6 to 3.0 (×10^-29) cm⁶/sec; a median value of 2.2×10^-29 cm⁶/sec at all values of E/N was used to obtain the above values of the other rate coefficients. The reduced mobility (and its standard deviation) for Li⁺ in N₂ was found to be 3.87±0.13 cm²/V sec; for Li⁺·N₂ in N₂, 2.04±0.12 cm²/V sec; and for Li⁺·2N₂ in N₂, 1.96±0.12 cm²V sec.