Femtosecond transient-grating spectroscopy with heterodyne detection was employed to characterize the nonradiative decay pathway in beta-carotene from the S2 (1(1)B(u)(+)) state to the S1 (2(1)A(g)(-)) state in benzonitrile solution. The results indicate definitively that the S-2 state populates an intermediate state, S-infinity, on an ultrafast time scale prior to nonradiative decay to the S-1 state. Numerical simulations using the response function formalism and the multimode Brownian oscillator model were used to fit the absorption and dispersion components of the transient-grating signal with a common set of parameters for all of the relevant Feynman pathways, including double-quantum coherences. The requirement for inclusion of the S-x state in the nonradiative decay pathway is the observed fast rise time of the dispersion component, which is predominantly controlled by the decay of the stimulated emission signal from the optically prepared S-2 state. The finding that the excited-state absorption spectrum from the S-x state is significantly red-shifted from that of S-2 and S-1 leads to a new assignment for the spectroscopic origin of the S-x state. Rather than assigning S-x to a discrete electronic state, such as the B-1(u)- state suggested in previous work, it is proposed that the Sx state corresponds to a transition-state-like structure on the S-2 potential surface. In this hypothesis, the 12 fs time constant for the decay of the S-2 state corresponds to a vibrational displacement of the C-C and C-C bond-length alternation coordinates of the conjugated polyene backbone from the optically prepared Franck-Condon structure to a potential energy barrier on the S-2 surface that divides planar and torsionally displaced structures. The lifetime of the S-x state would be associated with a subsequent relaxation along torsional coordinates over a steep potential energy gradient toward a conical intersection with the S-1 state. This hypothesis leads to the idea that twisted structures with intramolecular charge-transfer character along the S-2 torsional gradient are active in excitation energy-transfer mechanisms to (bacterio)chlorophyll acceptors.