ROTATIONAL PARAMETERS OF THE 1ST TORSIONAL STATE OF ETHANE FROM LOWER STATE COMBINATION DIFFERENCES IN V9+V4-V4

Using interferometric spectra obtained on the McMath Solar Telescope FTS spectrometer in double pass configuration (0.0025 cm-1 resolution), the ν9 + ν4 - ν4 hot band of ethane has been assigned. The torsional splittings, on the order of 0.1 cm-1, are clearly resolved. A total of 556 lower state combination differences yield the B4σ values 0.6605099(73), 0.6605005(44), 0.6604929(76), and 0.6604846(54) cm-1 for σ = 0, 1, 2, 3, respectively. D4σJ is determined to be 1.0261(68), 1.0214(37), 1.0158(49), and 1.0147(74) × 10-6 cm-1, respectively. D4σJK yields 2.741(15), 2.724(18), 2.725(13), and 2.677(18) × 10-6 cm-1. Analysis of the individual σ-state results is presented. An expression is presented which characterizes the torsional dependence of the rotational constants; coefficients in the expression are determined by least-squares analysis of the rotational constants determined from analysis of the ν9 + ν4 - ν4 band and the rotational parameters of the ground state. The B-value for 3ν4, σ = 0, is predicted to be 0.656007 cm-1 compared to a value of 0.656090(24) cm-1 in the literature. Predictions of higher excited torsional state rotational parameters are presented. © 1990.