Spectra of Some Symmetric-Top Molecules in the One- to Four-Millimeter Wave Region

Rotational transitions of several symmetric-top molecules have been measured in the 1 to 4 mm wave region. The molecular rotational constants for the most abundant isotopic species are: B0=8545.877 Mc/sec, DJ=2.960 kc/sec, DJK=162.9 kc/sec, for CH3CCH; B0=10 348.862 Mc/sec, DJ=11.3 kc/sec, DJK=—18.06 kc/sec, for CF3H; B0=4 594.262 Mc/sec, DJ=1.020 kc/sec, DJK=1.284 kc/sec, for OPF3; B0=7208.049 Mc/sec, DJ=7.556 kc/sec, DJK=—12.45 kc/sec, for Si28F3H; B0=2945.528 Mc/sec, DJ=0.3065 kc/sec, DJK=5.814 kc/sec, for CF3CN. These constants were found to predict all observed lines within the accuracy of measurement ∼±0.2 Mc/sec. Higher-order stretching terms are too small to measure in the present experiments.