Knowledge Bank

Room $(295\circ K)$ and low $(119\circ K)$ temperature spectra of the C-H stretching fundamentals of $C2H6$ have been recorded with Doppler-limited resolution using a tunable difference-frequency laser spectrometer. The low temperature spectrum of the dense $\nu 7$ and $\nu 5$ bands was taken to reduce contributions from torsional ``hot” band lines and to further verify the line assignment. The Doppler line narrowing at low temperature also reveals small unexpected doublet splittings in the $\nu 7$ band which are attributed to torsional tunneling because of the 2:1 intensity ratios for lines with K = 3n and 4:1 for lines with $K=3n\pm 1$. A quantitative explanation of this phenomenon is presently under investigation.