Pressure Effect in the HCN Bands in the Near Infrared

Contrary to the observations of Herzberg and Spinks it is found that all the lines of the HCN absorption band at 1.04μ are broadened equally by increase in HCN gas pressure. The half-widths increase linearly with pressure at the rate of 0.56 ${\mathrm{cm}}^{-1\mathrm{}}$ per atmosphere. This value is slightly less than that found by H. Becker for the first harmonic band of HCl, as is to be expected from the relative polarizabilities of the two molecules. The results indicate dispersion forces to be the predominant broadening influence.