The rotational structure of the X (2)A(1) (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(+)less than or equal to5 and K(a)(+)less than or equal to2 have been used to derive a purely experimental r(0) structure [r(CH)=(1.1049+/-0.0041) Angstrom, alpha(HCH)=(139.77+/-0.27) degrees]. Whereas the positions of the K-a(+)=0 and 1 levels are in good agreement with previous results, the positions of the K-a(+)=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 CH2 (X) over tilde B-3(1) 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. (C) 2003 American Institute of Physics.