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Photodissociation of $CH_{3}I^{+}$ to $CH_{3}^{+}$ is observed using the SRI laser-ion coaxial beams photo-fragment spectrometer. $^{1}$ The $CH_{3}I^{+}$ ions are produced by electron impact on $CH_{3}I$, accelerated to 4 keV, mass selected, and merged with a laser beam. The appearance of $CH_{3}^{+}$ photofragment ions is detected as a function of both laser wavelength and product ion kinetic energy. Predissociation of $CH_{3}I^{+}$ in eight vibronic bands of the $\tilde{A}^{2}A_{1} \leftarrow; \tilde{X}^{2}E_{1/2}$ system is observed at moderate resolution ($0.5 cm^{-1}$) over the wavelength range of 6100 – 5700 {\AA}. Kinetic energy analysis of the photofragments suggests the bands correspond to progressions in the C – I stretching frequency of the $\tilde{A}$ state and that two or more vibrational levels of this state lie below the $CH_{3}^{+} + I(^{2}P_{3/2})$ dissociation limit. Measurements in portions of these bands at high resolution ($0.003 cm^{-1}$) reveal a high density of transitions $(> 10$ transitions/$cm^{-1}$) and a pre-dissociation lifetime of $>$ 5ns. The rotational fine structure of the bands is fully resolved in the spectra. Photofragment kinetic energy measurements for individual rotational lines show the release of discrete amounts of kinetic energy and suggest a nonstatistical distribution of rotational energy in the dissociations.


$^{1}$ B.A. Huber, T. M. Miller, P.C. Cosby, H. D. Zeman, R. L. Leon, J. T. Moseley, and J. R. Peterson, Rev. Sci. Instrum. 48, 1306 (1977). Research supported by AFOSR.
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