A method recently developed for calculating vibrational spectral densities of molecules, previously tested successfully on H2O, is applied here to several larger molecules. The method relies on use of a time averaging procedure in the conventional semiclassical (SC) initial value representation (IVR) expression for the spectral density. The convergence of the SC-IVR average over the phase space of initial conditions (of classical trajectories) is greatly enhanced by time averaging and is generally achieved with as few as 1000 trajectories per degree of freedom. Furthermore, meaningful results can be obtained with only a single trajectory propagated for a long time. (For systems with chaotic dynamics, however, the phase space average converges more slowly.) Results for vibrational energy levels of H2CO, NH3, CH4, and CH2D2 are reported and compared with quantum mechanical calculations available in the literature. The accuracy of the time-averaged SC-IVR is very encouraging, with the vibrational energy levels consistently in agreement with the quantum results to a few parts in a thousand. (C) 2003 American Institute of Physics.