By performing nb inito calculations for the TCNE-HMB complex, we obtain the optimized geometry and the vibrational modes of the ground state. We find that symmetry is broken due to a formation of hydrogen bond between one of the hydrogen atoms of HMB and one of the nitrogen atoms of TCNE. We also find that all the donor-acceptor intermolecular modes are found in the frequency region less than 100 cm(-1). We identify donor-acceptor stretching mode at 59 cm(-1) and two TCNE vibrations at 167 and 170 cm(-1), which two modes are highly associated with the experimentally observed mode. Deuteriation effects are also investigated for this complex. We set up a new model for optical transitions, which consists of the two CT states and one ground state including 33 vibrational modes. On the basis of this new model, we analyze the steady state absorption and fluorescence spectra to tentatively obtain potential parameters. We find that the ratio of the transition moment of the CT2 state to that of the CT1 is about 0.3.