A strongly oscillating beam maser has been used to obtain 2 pi pulse excitation of the molecular beam as a whole. It is shown that when fast molecules in the molecular beam undergo pi pulse excitation, some slow molecules in the velocity distribution of the molecular beam undergo 2 pi pulse excitation, and burn a narrow dip or hole in the wider spectral profile of fast molecules. The phenomenon may be generalized to other molecular beam systems, including a thermal beam.