Signal-to-noise ratio of FT-IR CO gas spectra

The minimum amount of a gaseous compound which can be detected and quantifi ed with Fourier transform infrared (FT-IR) spectrometers depends on the sig nal-to-noise ratio (SNR) of the measured gas spectra. In order to use low-r esolution FT-IR spectrometers to measure combustion gases like CO and CO2 i n emission and transmission spectrometry, an investigation of the SNR in CO gas spectra as a function of spectral resolution has been carried out. We present a method to (1) determine experimentally the SNR at constant throug hput, (2) determine the SNR on the basis of measured noise levels and Hitra n simulated signals, and (3) determine the SNR of CO from high to low spect ral resolutions related to the molecular linewidth and vibrational-rotation al lines spacing. In addition, SNR values representing different spectral r esolutions but scaled to equal measurement times were compared. It was foun d that the SNR was at a local minimum at a spectral resolution of 4 cm(-1). As a result of the investigations, we suggest that the specific spectral r esolution which smears out the vibrational-rotational line structure of the smaller molecules should be considered to be low (4 cm(-1) for CO).