A new method for the direct measurement of spectral line strengths and widths

Abstract

The most important sources of error incurred in the measurements of spectral-line parameters arise from uncertainty in the determination of the 100 per cent transmittance and in the distortion of the line profile by the spectrometer. These errors have been investigated numerically by passing an idealized spectrometer slit function over several assumed line profiles. In this way, families of correction curves have been constructed, from which spectral-line strengths, widths, and peak absorption coefficients may be determined from apparent values measured directly from the chart recorder. The effect of the form of the slit function has been investigated by using triangular, Gauss, Cauchy and combination Gauss-Cauchy slit functions. The effect of uncertainties in the line shape has been investigated by using Doppler, Lorentz, and Voigt line shapes. The correction procedure has been applied to the self- and nitrogen-broadened R(0) and P(1) lines in the first overtone band of hydrogen fluoride. The measurements were performed on collision-broadened lines near the linear region of growth; within experimental error, the line parameters were found to obey the Lorentz relation k P = S/Γπ. The measured self-broadened line widths indicate a non-Lorentz behavior because they do not vary linearly with pressure. When broadened by nitrogen, the line widths follow the expected linear dependence on pressure, well within experimental error.