Ion‐pair formation from photoexcited methanes, CH*4 →H− +CH+3 and CD*4 →D− +CD+3, has been studied by measuring the efficiency curves of H− and D− using synchrotron radiation. Ion pairs are produced both by direct dissociation and predissociation of the npt2 (n=3–5) Rydberg state converging to the à 2A1 state of CH+4/ CD+4. The 4pt2 and 5pt2 Rydberg states are observed here for the first time.
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