We present a detailed theoretical investigation of the structure and dynamics of the S-3 excited state of CS2. The excited state is treated using equation-of-motion coupled-cluster (EOM-CC) theory, and analytic gradients are used in determining the vibrational frequencies. Information from the structure calculations is used to construct a model potential surface. Time-dependent wave packet methods are used to generate the transition state spectrum corresponding to collinear CS2. The spectrum is comprised of transition state resonances which are assigned via a spectral quantization method. The energies and lifetimes of the spectral features are related to recent experimental measurements. (C) 1997 American Institute of Physics. [S0021-9606(97)02641-X].