The 351-nm photoelectron spectrum of the negative ion of 1,3-benzoquinodimethane (m-xylylene) is reported. Features are observed in the photoelectron spectrum corresponding to formation of the B-3(2), (1)A(1), and B-1(2) states of m-xylylene. The electron affinity of the triplet ground state is found to be 0.919 +/- 0.008 eV, and vibrational frequencies of 290, 540, and 1500 cm(-1) are obtained. The active modes are assigned to alpha-carbon bending, ring deformation, and methylene bending, respectively. The (1)A(1) state is found to lie 9.6 +/- 0.2 kcal/mol higher in energy than the ground state, in good agreement with theoretical predictions. Vibrational frequencies of 265, 1000, and 1265 cm(-1) are found for this state. The B-1(2) is estimated to be <21.5 kcal/mol higher in energy than the ground state. Density functional calculations have been carried out on the negative ion, indicating that the B-2(1) ion is a minimum on the potential energy surface, lying 2.9 kcal/mol lower in energy than the (2)A(2) ion, which is a transition state.