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</p

Self- and Air-Broadened Line Shape Parameters of ¹²CH₄ : 4500-4620 cm⁻¹

<p>Accurate knowledge of spectral line shape parameters is important for infrared transmission and radiance calculations in the terrestrial atmosphere. We report the self and air-broadened Lorentz widths, shifts and line mixing coefficients along with their temperature dependencies for methane absorption lines in the 2.2 <em>µ</em>m spectral region. For this, we obtained a series of high-resolution, high S/N spectra of 99.99% ¹²C-enriched samples of pure methane and its dilute mixtures in dry air at cold temperatures down to 150 K using the Bruker IFS 125HR Fourier transform spectrometer at JPL. The coolable absorption cell had an optical path of 20.38 cm and was specially built to reside inside the sample compartment of the Bruker FTS¹. The 13 spectra used in the analysis consisted of seven pure ¹²CH₄spectra at pressures from 4.5 to 169 Torr and six air-broadened spectra with total sample pressures of 113-300 Torr and methane volume mixing ratios between 4 and 9.7%. These 13 spectra were fit simultaneously using the multispectrum least-squares fitting technique². The results will be compared to existing values reported in the literature³.</p