1. T. Shimizu and C. C. Costain, “Observation of Saturation Dip in the Microwave Spectral Line”, to be submitted.
2. C. C. Costain, Can. J. Phys. 47, 2431 (1969).
3. T. Amano and T. Shimizu, “Observation of Transient Nutation Effect in Microwave Transitions of Ammonia Molecules”, to be published in J. Phys. Soc. Japan.
4. R. G. Brewer and R. L. Shoemaker, Phys. Rev. Letters 27, 631 (1971), Phys. Rev. A6 2001 (1972).
5. J. M. Levy, J. H.-S. Wang, S. G. Kukolich and J. I. Steinfeld, Phys. Rev. Letters 29, 395 (1972).