The potential-energy functions of the 1 B-1(u) and 2 (1)A(g) excited valence states of trans-buradiene have been characterised by the CASPT2 method. Based on these ah initio data, a vibronic-coupling model describing the conical intersection of the 1 B-1(u) and 2 (1)A(g) states has been constructed. UV resonance-Raman and absorption spectra have been calculated, employing the time-dependent approach. The time-dependent wave-packet calculations reproduce the expected ultrafast (approximate to 30 fs) radiationless decay of the optically bright 1 B-1(u) state into the dark 2 (1)A(g) state.