Second Derivative Tunable Diode Laser Spectrometry for Line Profile Determination I. Theory

A technique of using second derivative spectra has been developed by which accurate infrared line widths and shapes may be measured using a single-beam tunable diode laser spectrometer both for a flat background and in the presence of a sloping background. It is shown that there exist easily measured parameters of the second derivative line profile which are independent of a small linearly sloping background. A procedure was developed which uses sets of precomputed model line profiles to allow an estimate of the true linewidth of a line to be derived from the second derivative spectrum. The accuracy of this technique is limited by the accuracy with which the second derivative line profile can be measured.