Association reactions at low pressure. IV. The HC₃N⁺/HC₃N system Available to Purchase

The reactions between HC₃N⁺ and HC₃N, and between HC₅N⁺ and HC₃N have been examined at pressures from 1×10⁻⁷ to 1×10⁻³ Torr by ion cyclotron resonance mass spectrometry. The reaction between HC₃N⁺ and HC₃N has both a bimolecular reaction path and a termolecular reaction path. The overall bimolecular reaction rate coefficient was found to be 1.3×10⁻⁹ cm³ s⁻¹. The primary product, HC₅N⁺, represents 90% of the product ions, while the minor products HC₆N⁺₂ and H₂C₆N⁺₂ each represent 5%. The termolecular association rate coefficient was 3.7×10⁻²⁴ cm⁶ s⁻¹ with He as the third body. From double resonance experiments the mean lifetime of the collision complex was determined to be 180 μs. HC₅N⁺ was found to react with HC₃N and form the adduct ion H₂C₈N⁺₂ through both bimolecular and termolecular channels. The bimolecular rate coefficient was 5.0×10⁻¹⁰ cm³ s⁻¹ and the termolecular rate coefficient was observed to be 1.2×10⁻²² cm⁶ s⁻¹ with HC₃N as the third body. With He as the stabilizing molecule, the termolecular rate coefficient was 6.0×10⁻²⁴ cm⁶ s⁻¹. The mean unimolecular lifetime of the collision complex was estimated to be ≥15 μs and the mean radiative lifetime for the radiative association channel was found to be ≥89 μs. HC₅N⁺ was found to be formed with excess internal energy and did not react by bimolecular association until relaxed by several nonreactive collisions with HC₃N.