Calibration of far-infrared spectrometers in the 100–200-cm^−1 region with the ν_5–ν_4 band of acetylene

Abstract

The R branch of the nu(5)-nu(4) difference band of acetylene, 12C(2)H(2), is recommended as a calibration standard for the 100-200-cm(-1) region. The lines are split by l-type doubling into pairs with a 3:1 intensity ratio, but this can only be observed under high resolution. The position of the calculated maximum of each blended line contour is displaced by the l-type doubling from the accurately calculated wavenumber of the more intense component of each J pair, but not by more than one-fifteenth of the spectral slit width. It is recommended that values calculated from constants derived from high resolution mid-ir measurements be used for calibration.