The first mass-analyzed threshold ionization (MATI) spectra from molecular excited triplet states have been collected for benzene and perdeuteriobenzene from the 3 B 1u , lowest triplet state. From these spectra, the C 6 H 6 3 B 1u state energy is found to be 29 627 ( 12 cm -1 and the C 6 D 6 3 B 1u state energy is found to be 29 828 ( 12 cm -1 . The MATI spectrum for each species was collected from 1000 cm -1 below the ionization threshold to ∼2000 cm -1 above the threshold. Hot band structure allowed for the first higher-resolution gas phase vibrational measurement of the ν 1 , ν 8 , and ν 6 frequencies in the 3 B 1u state. They were found at 927, 229, and 575 cm -1 for the protonated molecule and at 832, 200, and 528 cm -1 for the deuterated molecule, respectively. New vibrational structure has also been observed in the cation ground state of both molecules.