New investigation of the ν3 C–H stretching region of 12CH4 through the analysis of high temperature infrared emission spectra

Abstract

The ν C-H stretching region of methane was reinvestigated in this work using high temperature (620-1715 K) emission spectra recorded in Rennes at Doppler limited resolution. This work follows our recent global analysis of the Dyad system Δn = ±1 (1000-1500 cm), with n being the polyad number [B. Amyay et al., J. Chem. Phys. 144, 24312 (2016)]. Thanks to the high temperature, new assignments of vibration-rotation methane line positions have been achieved successfully in the Pentad system and some associated hot bands (Δn = ±2) observed in the spectral region 2600-3300 cm. In particular, rotational assignments in the cold band [Pentad-ground state (GS)] and in the first related hot band (Octad-Dyad) were extended up to J = 30 and 27, respectively. In addition, 1525 new transitions belonging to the Tetradecad-Pentad hot band system were assigned for the first time, up to J = 20. The effective global model used to deal with the new assignments was developed to the 6th order for the first three polyads (Monad, Dyad, and Pentad), and to the 5th order for both the Octad and the Tetradecad. 1306 effective parameters were fitted with a dimensionless standard deviation σ = 2.64. The root mean square deviations d obtained are 4.18 × 10 cm for the Pentad-GS cold band, 2.48 × 10 cm for the Octad-Dyad, and 1.43 × 10 cm for the Tetradecad-Pentad hot bands.

Atlas of Experimental and Theoretical High-temperature Methane Cross Sections from T = 295 to 1000 K in the Near-infrared

“…The Astrophysical Journal Supplement Series, 240:4 (11pp), 2019 January Wong et al Much effort has recently been devoted to the calculation of high-temperature methane data such as the UCL ExoMol list (Yurchenko et al 2014(Yurchenko et al , 2017 using ab initio intensities, and the Dijon MeCaSDa list accessible via the VAMDC web portal (Ba et al 2013;Dubernet et al 2016) based on extrapolation of experimental analyses (Amyay et al 2018), and the TheoReTS list using RNT-2017 ab initio intensities. Quite significant discrepancies exist among these calculations, as discussed by .…”

Calculated spectroscopic databases for the VAMDC portal: New molecules and improvements

“…groups of interacting vibrational levels. A polyad can either be a single vibrational level (for instance an isolated fundamental level) or a more complex set of interacting levels like in the methane case [17]. Depending on the molecule and on the level of analysis that has been reached, different polyad schemes are used.…”

High enthalpy source dedicated to quantitative infrared emission spectroscopy of gas flows at elevated temperatures

“…scitation.org/journal/rsi high-temperature spectroscopic studies performed using our high enthalpy source. 50,51 Then, in the first step, the most intense lines [≥1 × 10 −22 cm −1 /(molecule cm −2 )] were selected and their absorption cross sections σ k (ν, T hot ) were fixed [initially to their calculated value using Eq. (4)] in order to determine the gas density and the graphite emissivity.…”