Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He-*(2 S-3) metastable atoms indicates that interaction potentials between p-benzoquinone and He-*(2 S-3) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the Cdouble bondO groups for in-plane and out-of-plane directions, while repulsive interactions were found around CH bonds and the benzenoid ring. Assignment of the first four ionic states of p-benzoquinone and an analogous methyl-substituted compound was examined with CEDPICS and anisotropic distributions of the corresponding two nonbonding oxygen orbitals (n(O)(+),n(O)(-)) and two pi(CC) orbitals (pi(CC)(+),pi(CC)(-)). An extra band that shows negative CEDPICS was observed at ca. 7.2 eV in Penning ionization electron spectrum. (C) 2004 American Institute of Physics.