The structures of C2H+ and C2H+2 as measured by Coulomb explosion imaging

The structures of ethynyl and acetylene cations were investigated utilizing the Coulomb explosion imaging method. The geometrical probability density functions for the bending modes were obtained for the protonated and deuterated forms of each species. Detailed analyses of the data reveal that both the measured linear equilibrium geometries and the observed extent of the correlated bending vibrations agree with ab initio calculations for C2H+2 and C2D+2. C2H+ and C2D+ are found to be linear, but the extent of the bending amplitudes are by far larger than the corresponding theoretical predictions.