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

Abstract

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, D_J=2.96₀ kc/sec, D_JK=162.9 kc/sec, for CH₃CCH; B₀=10 348.86₂ Mc/sec, D_J=11.3 kc/sec, D_JK=—18.0₆ kc/sec, for CF₃H; B₀=4 594.26₂ Mc/sec, D_J=1.02₀ kc/sec, D_JK=1.28₄ kc/sec, for OPF₃; B₀=7208.04₉ Mc/sec, D_J=7.55₆ kc/sec, D_JK=—12.4₅ kc/sec, for Si²⁸F₃H; B₀=2945.52₈ Mc/sec, D_J=0.306₅ kc/sec, D_JK=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.