A gas cell for high-temperature and high-pressure absorption spectroscopy: Application to CO₂ near 2.7 µm

This paper presents the design, validation, and application of a new optically accessible gas cell capable of supporting high-pressure and high-temperature environments. The new cell enabled spectroscopic studies to be performed at pressures up to 200 atm and temperatures up to 1300 K. The cell was manufactured from a nickel alloy material to allow for high-temperature operation. Long sapphire rods allowed optical access to the high-pressure and high-temperature test region while maintaining all seals at a low temperature outside the heated zone. Validation tests were conducted to demonstrate a highly uniform temperature distribution across the 10-cm optical path length. Subsequently, absorbance measurements were performed for CO₂ in air near 2.7 µm under wide range of conditions (i.e., up to 1110 K and 50 atm), and the obtained results were compared with the Voigt profile simulations obtained using the HITRAN/HITEMP databases. Furthermore, a series of low-pressure absorbance measurements were performed at temperatures ranging from 300 to 1100 K to comprehensively characterize the spectroscopic parameters (i.e., line strength, air-broadening coefficient, and temperature exponent) for two selected CO₂ transitions. The obtained parameters were found to be in excellent agreement with the values reported in the HITRAN database. This new gas cell will be expected to enable future spectroscopic studies of various molecules, particularly at high temperatures and pressures.