The radiative decay of excited CHminus;trapped in a radio frequency ion trap was measured, and the total excited state population was probed by observing the depletion of trapped CHminus;caused by photodetachment at 1.16 eV, below the expected electron affinity for the ground3Sgr;minus;state. The signal decayed biexponentially with time. We assigned the long lived state (lifetime 5.9+0.8, minus;0.6thinsp;s) as the metastableathinsp;1Dgr; state previously identified in the photoelectron spectrum. The fast decay, with a lifetime of 1.75plusmn;0.15 ms, was attributed to the first excited vibrational level of the ground3Sgr;minus;state, in good agreement with a theoretical result by Manz, Zilch, Rosmus, and Werner. These results support the electron affinity of 1.238 eV for CHminus;obtained by Kasdan, Herbst, and Lineberger from photoelectron spectroscopy, and contradict the value of 0.74 eV determined by Feldmann from photodetachment spectroscopy.
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