Rotational Temperature Estimation of CO at High Temperatures by Graphical Methods Using FT-IR Spectrometry

Abstract

Rotational temperatures are obtained from gas-phase Fourier transformed infrared spectra of CO with the use of graphical methods over the temperature range 302 to 773 K. Peak absorbances of individual rovibrational transitions are corrected for instrumental distortion and are then fit to a Boltzmann distribution to obtain the rotational temperature of the gas. A solution to the convolution integral for FT-IR spectrometry is obtained by numerical integration. The equation relating observed peak absorbance, A_obs, to true peak absorbance, A_pm, ranging from one to five true peak absorbance units for triangularly apodized spectra is:

$A_{pm}\propto A_{obs}^{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}1.818}{\rho }^{1.748}$

where the resolution parameter, ρ, is equal to 1/(2Δγ_m), γ_m is the half-width at half-height (HWHH) of the absorption line in question, and Δ is the maximum optical retardation of the interferometer (here equal to 1 cm). In all cases, temperatures obtained by graphical analysis yielded gas temperatures within 10% of the actual temperatures. Experiments were also conducted to determine the CO rotational temperature in a premixed, low-pressure (64 Torr) CH₄/N₂O flame. CO temperatures for the premixed flame ranged from 1500 to 1700 K, indicating a large transferral of heat from the flame to the burner chamber.