Knowledge Bank

The half width of a collision-broadened absorption line can be expressed as $\Delta \nu =apa+bpb$ where $p$ denotes the partial pressure of either the absorbing gas, $pa$, or of a foreign gas, $pb$. The ratio, $b/a$, can be obtained from measurements at the line center using the square root law, or obtained without slit corrections when measurements are made on a wing of a line. The ratios $b/a$ for the HF fundamental lines broadened with $SO2$ have been obtained with both types of measurements. The values are consistent with each other. The ratios, b/a, decrease rapidly with J for the R(0) through R(5) lines. With $N2$ and $O2$ broadening the fractional decrease in b/a with increasing J is somewhat less pronounced, but still appreciable.