Self-Broadening in the14μBand of HCN

Abstract

The intensity distribution in the positive branch of the ${14}_{\mu }$ HCN band has been measured at pressures of 2.5 cm, 16 cm, 40 cm, and 58 cm. Because of the large permanent dipole moment of this molecule, there is considerable line broadening at these pressures. The overlapping of lines, slit width effects, and finite thickness of the absorbing layer of gas are taken into account in relating the theoretical line widths to the intensity distribution. The two constants giving the effective slit width and the absolute vibration intensity are determined from the low pressure lines, and these constants with the theoretical line widths determine the intensity distribution throughout the band. Reasonably good agreement is found at all pressures, and no systematic disparity of theory and experiment is indicated. The predicted shifts in the lines, which are just within the limits of detection, are in qualitative agreement with the observed values. The absolute value of the dipole strength of this vibration transition is determined.