Nonlinearity of Beer's law in gas-phase FT-IR spectroscopy

The nonlinear deviation from Beer's law due to a finite instrumental resolu tion has been studied by taking the shape of the spectrum into account. The phenomenon has been studied as a function of resolution theoretically and by simulations. The results show that the nonlinearity is constant in the p art of interferogram between the vibrational structure and rotational struc ture since there is very small signal in that region. The study suggests th at the optimal resolution has to be decided by the width of the vibrational bands rather than by the width of the rotational lines.