Quantifying methane vibrational and rotational temperature with Raman scattering

This work describes the theoretical basis and implementation of the measurement of vibrational (T vib) and rotational (T rot) temperatures in CH4 by fitting spontaneous Raman scattering spectra in the Pentad region. This method could be applied for thermal equilibrium temperature measurements applications, e.g. in combustion, or vibrational-rotational non-equilibrium applications, such as in plasma chemistry. The method of calculating these temperatures is validated against known temperature thermal equilibrium spectra up to 860 K from published data, giving an estimated relative error of 10%. This demonstrates that both the calculated stick spectrum and the algorithm to determine T vib and T rot for CH4 is robust to 860 K, but we expect it is valid to 1500 K. Additionally, a number of non-equilibrium spectra generated with a pulsed microwave plasma are fitted to find T vib and T rot, further demonstrating the applicability of this method in fitting non-equilibrium spectra.</p

STATUS ON THE GLOBAL VIBRATION-ROTATION MODEL IN ACETYLENE

S. Robert, M. Herman, A. Fayt, A. Campargue, S. Kassi, A. Liu, L. Wang, G. Di Lonardo, and L. Fusina, Mol. Phys., \underline{106A. Jolly, Y. Benilan, E. Cane, L. Fusina, F. Tamassia, A. Fayt, S. Robert, and M. Herman, J.Q.S.R.T., \underline{109Author Institution: Service de Chimie quantique et Photophysique CP160/09; Faculte des Sciences, Universite Libre de Bruxelles (U.L.B.), Av. Roosevelt, 50, B-1050; Bruxelles, Belgium; Laboratoire de Spectroscopie Moleculaire, Universite; Catholique de Louvain, Chemin du Cyclotron, 2, B-1348 Louvain-La-Neuve, BelgiumWe have developed a global model to deal with all vibration-rotation levels in acetylene up to high vibrational excitation energy, typically up to 9000 wavenumbers. It has been applied to a number of isotopologues, considering all known vibration-rotation lines published in the literature, for various purposes such as line assignment, 2581 (2008).} and astrophysical applications$^{b}$, 2846 (2008).}. Coriolis interaction is now systematically being introduced in the model. Recent results concerning the analysis of hot emission FTIR spectra recorded around 3 microns by R. Georges et al. at the University of Rennes (France) and of CW-CRDS spectra recorded around 1.5 microns by A. Campargue et al. at the University of Grenoble (France) will help illustrate the role of this vibration-rotation coupling in the global polyad scheme

ROTATIONAL DEPENDENCE OF INTRAMOLECULAR DYNAMICS IN ACETYLENE AT LOW VIBRATIONAL EXCITATION AS DEDUCED FROM HIGH RESOLUTION SPECTROSCOPY

Author Institution: Department of Chemistry, The University of Akron, Akron OH 44325-3601; Laboratoire de Chimie Quantique et Photophysique, Universite libre de; Bruxelles, B-1050 Brussels, BelgiumThe link between energy-resolved spectra and time-resolved dynamics is explored quantitatively for acetylene ($^{12}C_{2}H_{2}$), $\~{X}^{1}\Sigma_{g}^{+}$ with up to 8,600 \wn of vibrational energy. This comparison is based on the extensive knowledge of the vibration-rotation energy levels and on the model Hamiltonian used to fit them to high precision.}, 114301 (2009).} Simulated intensity borrowing features in high resolution absorption spectra and predicted survival probabilities for intramolecular vibrational redistribution (IVR) are first investigated for the $\nu_{4}+\nu_{5}$ and $\nu_{3}$ bright states, for $J =$ 2, 30 and 100. The dependence of the results on the rotational quantum number and on the choice of vibrational bright state reflects the interplay of three kinds of off-diagonal resonances: anharmonic, rotational $l-$type, and Coriolis. The dynamical quantities used to characterize the calculated time-dependent dynamics are the dilution factor $\phi_{d}$, the IVR lifetime $\tau_{IVR}$, and the recurrence time $\tau_{rec}$. For the two bright states $\nu_{3}+2\nu_{4}$ and $7\nu_{4}$, the collisionless dynamics for thermally averaged rotational distributions at $T$= 27, 270 and 500 K were calculated from the available spectroscopic data. For the $7\nu_{4}$ bright state, an apparent irreversible decay of is found. In all cases, the model Hamiltonian allows a detailed calculation of the energy flow among all of the coupled zeroth-order vibration-rotation states

High temperature spectroscopy of ethyne and stellar spectra modelling

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Spectroscopie haute température pour Jupiter chauds

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New investigation of the ν 3 C-H stretching region of 12CH4 through the analysis of high temperature infrared emission spectra

International audienceThe ν3 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-1), 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-1. 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 dRMS obtained are 4.18 × 10-3 cm-1 for the Pentad-GS cold band, 2.48 × 10-3 cm-1 for the Octad-Dyad, and 1.43 × 10-3 cm-1 for the Tetradecad-Pentad hot bands

Vibration-rotation pattern in acetylene. II. Introduction of Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 microns

This paper was selected by the editors of the Journal of Chemical Physics as one of the few of the many notable JCP articles published in 2009 that present ground-breaking researchinfo:eu-repo/semantics/publishe

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

International audienceThe High Enthalpy Source (HES) is a novel high temperature source developed to measure infrared line-by-line integrated absorption cross sections of flowing gases up to 2000 K. The HES relies on a porous graphite furnace designed to uniformly heat a constant flow of gas. The flow compensates thermal dissociation by renewing continuously the gas sample and eliminating dissociation products. The flowing characteristics have been investigated using computational fluid dynamics simulation confirming good temperature uniformity. The HES has been coupled to a high-resolution Fourier transform spectrometer to record emission spectra of methane at temperatures ranging between 700 and 1400 K. A radiative model has been developed to extract absolute line intensities from the recorded spectra. © 2019 Author(s)