High resolution spectroscopy and the first global analysis of the Tetradecad region of methane 12CH4

Abstract

We present the first detailed analysis of the infrared spectrum of methane (12)CH4 in the so-called Tetradecad region from 2.1 to 1.6 μm (4760-6250 cm(-1)). New experimental high resolution FTIR spectra at 78 K and at room temperature combined with improved theoretical modeling have allowed quantum assignments to be greatly extended in this region. A global fit of all assigned lines of (12)CH4 in the 0-6200 cm(-1) region has been performed. In the end, 3012 line positions and 1387 intensities of 45 individual subbands of the Tetradecad were modeled up to J = 14. The root mean square deviations were 0.023 cm(-1) for line positions and 13.86% for line intensities in the Tetradecad region itself. Although this analysis is still preliminary, it is already sufficient to characterize the stronger bands throughout the whole of the Tetradecad. The calculated integrated intensity of the polyad is 1.399 × 10(-19) cm(-1)/(molecule cm(-2)) at 296 K. A "definitive" theoretical modeling of this spectral region of methane requires further work, but the present success substantially improves our understanding of methane spectroscopy as needed to interpret planetary atmospheres. Lines pertaining to three-fourths of the 60 sub-vibrational bands in this polyad have been assigned.

Titan’s atmosphere as observed by Cassini/VIMS solar occultations: CH4, CO and evidence for C2H6 absorption

“…CH 4 lines with m < 5853 cm À1 (k > 1.708 lm) were extracted from the VAMDC database (http://vamdc.icb.cnrs.fr/PHP/methane.php) and are based on a global analysis of the methane spectrum as described in Albert et al (2009) and Boudon et al (2006). (k > 3.11 lm), a linelist provided by A. Nikitin (private communication) between 3212 and 5000 cm À1 (2 lm < k < 3.11 lm), based on the works by Nikitin et al (2002Nikitin et al ( , 2006Nikitin et al ( , 2013, and finally Campargue et al (2013) above 5853 cm À1 (k < 1.71 lm).…”

Self- and air-broadened line shapes in the 2ν3 P and R branches of 12CH4

“…Complete and reliable line shape parameters of air-broadened methane measured as a function of temperature are critical not only for the correct interpretation of the observed atmospheric spectrum but also for the development of a reliable and robust quantum mechanical model for pressure broadening. The methane spectrum between 1.6 and 2.1 µm is characterized as the Tetradecad polyad which consists of 14 vibrational states involving 60 sub-vibrational levels with transitions spanning the 4750−6300 cm −1 interval [16,17]. The 2v 3 band near 6000 cm −1 is the strongest, but its line positions and intensities cannot be accurately predicted without considering interactions with the nearby states.…”

“…[18] and the references therein), the quantum assignments of many observed features remain unidentified. Efforts to interpret and calculate the positions and intensities for this polyad are ongoing, using both Hamiltonian [16,17] and ab initio formalisms [19,20].…”

Synchrotron-based highest resolution FTIR spectroscopy of chlorobenzene

“…Further important questions can be addressed by the study of molecules important for the spectroscopy of the Earth's atmosphere [16][17][18][19][20][21][22][23][24]. In the past, much high resolution spectroscopic work has concentrated on relatively simple atmospheric trace gases such as ozone [18], methane [20][21][22][23][24] or some of the simpler fluoro-chloro-hydrocarbons [25], to name just a few selected examples from a very large body of work usually based on FTIR spectroscopy with conventional light sources.…”