Two and one-half decades ago Schmidt and Quade reported their results of the microwave spectroscopic studies of CH 3 CH 2 SH, CH 3 CH 2 SD, and CH 2 DCH 2 SH, both methyl symmetric and asymmetric conformations for the latter species, and first excited state spectra for both trans-and gauche-CH 3 CH 2 SH and CH 3 CH 2 SD (1). Spectra for both the trans and gauche conformations were identified, assigned, and analyzed. Among the things determined from the analyses were the gauche tunneling energy, a molecular structure that was good for both conformations, components of the electric dipole moment, the x-y and x-z product of inertial coefficients D and E, the V 3 methyl barrier to internal rotation for trans-CH 3 CH 2 SH, the gauche-trans, gauche-gauche, and trans-trans energy differences from relative intensity measurements, and the potential energy coefficients for the hydroxyl internal rotation.
Recently we have used an internal axis method (IAM) (2) for calculation of the torsional-rotational term values for five isotopic species of ethyl alcohol (3). The results were as much negative as positive in the sense that the IAM, with its seven inertial constants plus three potential energy coefficients, did not in any way improve the spectral analyses over the parametric methods of analysis (4) based upon the isolation of the trans and gauche effective rotational blocks within the context of the framework fixed-axis method (FFAM) (5). The positive feature was that the so-called nonrigidity terms could be evaluated and improved values were obtained for the gauche tunneling energy in conjunction with the hydroxyl internal-rotation potential energy coefficients.