The reactions between HC3N+and HC3N, and between HC5N+and HC3N have been examined at pressures from 1times;10minus;7to 1times;10minus;3Torr 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 1.3times;10minus;9cm3thinsp;sminus;1. The primary product, HC5N+, represents 90percnt; of the product ions, while the minor products HC6N+2and H2C6N+2each represent 5percnt;. The termolecular association rate coefficient was 3.7times;10minus;24cm6thinsp;sminus;1with He as the third body. From double resonance experiments the mean lifetime of the collision complex was determined to be 180 mgr;s. HC5N+was found to react with HC3N and form the adduct ion H2C8N+2through both bimolecular and termolecular channels. The bimolecular rate coefficient was 5.0times;10minus;10cm3thinsp;sminus;1and the termolecular rate coefficient was observed to be 1.2times;10minus;22cm6thinsp;sminus;1with HC3N as the third body. With He as the stabilizing molecule, the termolecular rate coefficient was 6.0times;10minus;24cm6thinsp;sminus;1. The mean unimolecular lifetime of the collision complex was estimated to be ge;15 mgr;s and the mean radiative lifetime for the radiative association channel was found to be ge;89 mgr;s. 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.
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