DIODE LASER SPECTRA OF THE TORSIONAL SPLITTINGS IN THE ν9 BAND OF ETHANE: TORSION-VIBRATION-ROTATION INTERACTIONS AND THE BARRIER TO INTERNAL ROTATION

Diode laser spectra of most of the Q branches of the ν9 band of ethane from RQ8–PQ15 have been recorded. The Q branches RQ0–RQ4 were deconvoluted to yield an effective resolution of (0.5–1.0)×10−3 cm−1 FWHM. Torsional splittings were observed for most lines. In contrast to predictions based on first order theory, the splittings which range from (2–53)×10−3 cm−1, have a marked J and K dependence. A second order theory of torsion‐vibration‐rotation interaction between ν9 and 3ν4 is developed, which fits the splittings with an rms error of 0.0006 cm−1, using only three adjustable parameters: the barrier to internal rotation in ν9, the energy difference between ν9 and 3ν4, and an effective coupling constant. The barrier to internal rotation in ν9 is found to be 1123±10 cm−1.