Microwave Spectrum and Barrier to Internal Rotation in CF3SiF3

The microwave spectrum of CF₃SiF₃ has been analyzed. The ground‐state constants are $B_0\text{=1328.464± 0.001\hspace{0.17em}}\mathrm{MHz}$ , and $D_J\text{=0.09± 0.05\hspace{0.17em}}\mathrm{kHz}$ . An extensive series of torsional satellite lines has been studied in some detail. The barrier to internal rotation is found to be $\text{489± 50\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ , corresponding to a torsional frequency of $\text{37.0± 2.0\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . The lowest degenerate rocking mode has been determined as $\text{158± 12\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . Other vibrational fundamentals are discussed.