Dipole-bound CH3CN- ions: temperature dependence of ion production rates and lifetimes

The formation of long-lived (tau less, similar10 mus) dipole-bound CH(3)CN(-) ions through electron transfer in K(14p)CH(3)CN collisions is investigated as a function of target temperature. The rate for their formation is observed to decrease steadily with increasing target temperature. The results are consistent with earlier suggestions that only target molecules in the ground vibrational state and low-lying rotational states can form long-lived dipole-bound anions. For CH(3)CN, the data indicate that creation of long-lived ions requires that the target molecules be in states with rotational quantum numbers j less, similar20. The measurements further demonstrate that the lifetime of the longest-lived (tau greater, similar50 mus) ions is limited by blackbody-radiation-induced photodetachment.