Strong thermal nonequilibrium in hypersonic CO and CH4 probed by CRDS

Abstract

A new experimental setup coupling a High Enthalpy Source (HES) reaching 2000 K to a cw-cavity ring-down spectrometer has been developed to investigate rotationally cold hot bands of polyatomic molecules in the [1.5, 1.7] μm region. The rotational and vibrational molecular degrees of freedom are strongly decoupled in the hypersonic expansion produced by the HES and probed by cavity ring-down spectroscopy. Carbon monoxide has been used as a first test molecule to validate the experimental approach. Its expansion in argon led to rotational and vibrational temperatures of 6.7 ± 0.8 K and 2006 ± 476 K, respectively. The tetradecad polyad of methane (1.67 μm) was investigated under similar conditions leading to rotational and vibrational temperatures of 13 ± 5 K and 750 ± 100 K, respectively. The rotationally cold structure of the spectra reveals many hot bands involving highly excited vibrational states of methane.

Line shape in a free-jet hypersonic expansion investigated by cavity ring-down spectroscopy and computational fluid dynamics

“…In view of this, spectroscopic measurements are carried out for hypersonic jet of carbon monoxide and argon using cavity ring-down spectroscopy (CRDS). These studies are continuation of the earlier findings of Louviot et al [12] where as well double peak structure of absorption lines had been observed for carbon monoxide in CRDS based measurements. Therefore present investigations specifically deal with analysis of absorption line shapes for line of sight spectroscopic measurements.…”

“…Experiments are carried out in an experimental facility having a High Enthalpy Source (HES) connected to a vacuum chamber [12,13]. In the present studies, carbon monoxide (Air Liquide, 99.998% purity) is used as the seeding gas (5% by mass) and argon (Air Liquide, 99.998% purity) as the carrier gas (95% by mass).…”

“…are expected tohave differential contributions from these regions. Apart from this, since present experiments are conducted for high stagnation temperature conditions, it has led to strong thermal non-equilibrium[12] in the jet. Therefore, clustering of carbon monoxide is disregarded due to freezing of vibrational temperature in the expansion process.…”

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

“…The emergence of new experimental techniques such as the High Enthalpy Source (HES), developed by R. Georges and coworkers, coupled to a high-resolution Fourier transform spectrometer (FTS) allows the recording of high temperature emission spectra of polyatomic molecules (C 2 H 2 and CH 4 ) [33,34,35] up to about 2000 K. Recently, a new experimental setup coupling the HES to a cw-cavity ring-down spectrometer has been developed by the same group to investigate rotationally cold hot bands of polyatomic molecules in the 1.5-1.7 µm region [36]. Hargreaves et al developed an original approach to produce emission-corrected FTIR transmittance spectra of hot gases such as methane [37] and ethane [38].…”

Overtone spectroscopy of molecular complexes containing small polyatomic molecules

“…The latter set-up also uses cw-CRDS and the expansion is produced using a very large roots pumping system [265]. All experimental conditions are reported in [219].…”