| The methide ion, CH3−, is isoelectronic with ammonia, NH3. Two different autodetachment life times have been observed. Metastable autodetaching states of methide have been observed, with an autodetachment lifetime range of 17 to 667 μs using a fast coaxial ion-laser beam apparatus. The excited states responsible for autodetachment are presumably rotationally excited states. A rovibrational transition in methide has been observed at 3206.74 cm−1 using a fast coaxial ion-laser beam apparatus and sub-Doppler tuning techniques. The full-width-at-half-maximum was measured to be 22.65 MHz, which corresponds to a 7.03 ns lifetime of the vibrationally excited state. This is the first rovibrational measurement of its kind in an anion that is an oblate rotor. There are presently no theoretical calculations of the autodetachment mechanism or lifetimes of CH3 −. The collisional cross section was also measured for CH 3− and a calibrating ion O− to be 2.6 Å2 and 7.2 Å2 in two independent measurements, respectively. The ions are presumed to have collided with trace amounts of H2 and H2O. Double photodetachment cross section measurements have also been made in NO−, O 2−, and O− in the vacuum ultraviolet for the first time using a photon energy range of 18–100 eV. There has been much attention given to single photodetachment cross sections in atomic anions and threshold characterizations. However, there is no theory available to characterize double photodetachment cross sections for negative molecular ions. Nevertheless, the ZCC model, which is widely used in single photodetachment processes, provided reasonable results in predicting local extrema in the double detachment cross section, presumably at a crossover point where other channels within the inner shells opened up at higher photon energies. The observed double photodetachment may be the result of a Coster-Kronig process, but further investigation is needed for conclusive evidence of this. |
