DECONVLVING INFRARED SPECTRA BEYOND THE DOPPLER LIMIT

Abstract

Author Institution:In high-resolution molecular spectroscopy, the Doppler line width often poses a limitation on the resolution and thereby on the amount of information one can extract form the spectra. to enhance the effective resolution and attain effective line width smaller than the Doppler width, we have applied the deconvolution technique to the infrared spectra of medium size molecules (e.g., $C_{6}H_{6}$) measured with a difference frequency laser system, as well as to spectra of light molecules (e.g., $CH_{4}$) measured on a grating spectrometer. Using a Gaussian line shape function, we were able to enhance the resolution by a factor of 3 to 3.5 obtaining a linewidth of better than $1.5 \times 10^{-3} cm^{-1}$ in the deconvolved difference frequency laser spectrum. To test the reliability of the deconvolution routine, a synthetic many-line spectrum was generated and convolved with Gaussians of widths $4.3 \times 10^{-3} cm^{-1} (= 15$ points) and $1.4 \times 10^{-3} cm^{-1} (=5$ points) to match the linewidths of the measured and deconvolved spectra respectively. Deconvolution of the 15-point curve yielded a result almost indistinguishable from the 5-point curve. The effect of random noise and of slight background variations on the deconvolved curve was also studied. We conclude that, with proper care, quite reliable results can obtained by deconvolution of reasonably noise-free spectra