The rotational structure of the X̃ 2A1 (0,0,0) ground vibronic state of CH2+ has been observed by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy. Rotational levels with asymmetric top rotational quantum numbers N+⩽5 and Ka+⩽2 have been used to derive a purely experimental r0 structure [rCH=(1.1049±0.0041) Å,αHCH=(139.77±0.27) degrees]. Whereas the positions of the Ka+=0 and 1 levels are in good agreement with previous results, the positions of the Ka+=2 levels, which are observed for the first time, suggest that the theoretical description of the bending potential and of the Renner–Teller effect in CH2+ could still be refined. The single photon photoionization dynamics of the CH2X̃ 3B1 ground state is also consistent with a bent geometry for the ground state of CH2+. First PFI-ZEKE photoelectron spectra of CD2 are also presented.

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