Measuring Charge Distribution of Molecular Cations by an Atomic Coulomb Probe Microscope

Imaging the charge distributions and structures of molecules and clusters will promote the understanding of the dynamics of the quantum system. Here, we report a method by using an Ar atom as a tip to probe the charge distributions of benzene (Bz) cations in gas phase. Remarkably, the measured charge distributions of Bz^+ (\delta__\scriptstyle \rm H=0.204, \delta__\scriptstyle \rm C=-0.037) and Bz ^2+ (\delta__\scriptstyle \rm H=0.248, \delta__\scriptstyle \rm C=0.0853) agree well with the calculated Mulliken distributions, and the structures of Bz_2 is reconstructed by using the measured charge distributions. The structures of two Bz_2 isomers (T-shaped and PD isomers) can be resolved from the measured inter-molecular potential V(R) between two Bz ions, and the structures of Bz dimer agree well with the theoretical predictions.