Line Positions and Intensities of ¹³C¹²CH₆ in the 12.2 µm Region

<p>High-resolution, high signal-to-noise spectra of mono-substituted ¹³C-ethane (¹³C¹²CH₆) in the 12.2 <em>µ</em>m region have been recorded with a Bruker IFS 125HR Fourier transform spectrometer. Four of these spectra were recorded at three different temperatures between 130 and 208 K using a 99% ¹³C-enriched ethane sample contained in a 20.38-cm long coolable absorption cell¹. A multispectrum nonlinear least squares fitting technique²was used to fit the same intervals in these four spectra simultaneously to determine line positions and intensities. Similar to our previous analyses of ¹²C₂H₆spectra in this same region³, constraints were applied to accurately fit each pair of doublet components arising from torsional Coriolis interaction of the excited <em>ν</em>₁₂= 1 state with the nearby torsional <em>ν</em>₆= 3 state. Line intensities are reported for 1660 <em>ν</em>₁₂absorption lines for which the assignments are known, and integrated intensities are estimated as the summation of the measured values. The measured line positions and intensities are compared with values in recent editions of spectroscopic databases.⁴