Time evolution of vibrational temperatures in a CO₂glow discharge measured with infrared absorption spectroscopy

Abstract

Vibrational temperatures of CO 2 are studied in a pulsed glow discharge by means of time-resolved in situ Fourier transform infrared spectroscopy, with a 10 μs temporal resolution. A method to analyze the infrared transmittance through vibrationally excited CO 2 is presented and validated on a previously published CO 2 spectrum, showing good agreement between fit and data. The discharge under study is pulsed with a typical duty cycle of 5-10 ms on-off, at 50 mA and 6.7 mbar. A rapid increase of the temperature of the asymmetric stretch vibration (T 3 ) is observed at the start of the pulse, reaching 1050 K, which is an elevation of 550 K above the rotational temperature (T rot ) of 500 K. After the plasma pulse, the characteristic relaxation time of T 3 to T rot strongly depends on the rotational temperature. By adjusting the duty cycle, the rotational temperature directly after the discharge is varied from 530 to 860 K, resulting in relaxation times between 0.4 and 0.1 ms. Equivalently, as the gas heats up during the plasma pulse, the elevation of T 3 above T rot decreases strongly.

RADIS: A nonequilibrium line-by-line radiative code for CO2 and HITRAN-like database species

“…Dang et al [34] performed diode-laser transmittance measurements in a continuous-wave laser discharge at 20 mbar with 10% of CO 2 (in mass fractions). Klarenaar et al [7] successfully reproduced these transmittance measurements using a 3-temperature nonequilibrium model, with a T vib 1,2 , T vib 3 Treanor vibrational distribution, and a T rot rotational Boltzmann distribution. The translational temperature is assumed to be equal to the rotational temperature.…”

“…Carbon dioxide. The built-in spectroscopic constants reviewed by Klarenaar et al [7] were implemented for the three main isotopes of CO 2 , and were used to reproduce the validation case of Figure 13 in section 5. The rovibrational energies are then calculated with an uncoupled vibrating rotor model, using a first order anharmonicity correction for each of the three vibration modes considered (ω e x e1 , ω e x e2 , ω e x e3 ), and a second order correction for the centrifugal force (D, H).…”

“…We use this transmittance spectrum as a validation case for multi-temperature nonequilibrium calculations in RADIS, using the same input conditions as Klarenaar et al [7]. The line database is HITEMP-2010 [26], and the Dunham coefficients are the one given in Ref.…”

“…The line database is HITEMP-2010 [26], and the Dunham coefficients are the one given in Ref. [7]. However, we extend the nonequilibrium distribution to a 4-temperature distribution, with a T vib 1 , T vib 2 , T vib 3 Treanor distribution for vibrational levels, and a T rot Boltzmann distribution for rotational levels.…”

“…Klarenaar et al [7] developed a nonequilibrium CO 2 code with Boltzmann rotational distributions (T rot ) and mode-specific Treanor vibrational distributions (T vib1,2,3 ). They used line positions and line intensities from the HITEMP-2010 database, and calculated populations with rovibrational energies based on two-term Dunham expansions for vibration (ω e , ω e x e ) and three-term expansions for rotation (B, D, H), without vibration-rotation coupling terms.…”