Knowledge Bank

The shifts due to the presence of a foreign non-interacting gas of the spectral lines $P(4)-R(6)$ of the fundamental vibration-rotation band of hydrogen fluoride were measured. A constant HF pressure of 2.15 cm. of mercury was used, and to this was added $25,50,75,$ and 100 psi of $CO2$. For each line the shift was found to be proportional to the $CO2$ pressure. In the R branch of the band, the lines with $|m|$ equal to one or two were shifted to higher frequencies and the lines with $|m|$ greater than two were shifted to lower frequencies. In the P branch, for corresponding values of $|m|$, the lines were shifted in the opposite directions. However, the effect with $|m|$ greater than four in the P branch was not ascertained, due to the presence of a strong $CO2$ absorption band.