Knowledge Bank

All the lines of the far-infrared $SO2$ laser were assigned. These correspond to transitions involving pairs of resonant Levels in the ground electronic state, namely the $\nu 1$ + $\nu 2$, $J13,J-13$ and the $3\nu 2$, $J15,J-15$ levels, for J = 29, 30 and 31. The resonance depends on the anharmonic constant $k122$ and on the difference between the bind origins of $\nu 1$ + $\nu 2$ and $3\nu 2$. The former was deduced from the resonance observed in the microwave spectra of $\nu 1$ and $2\nu 2$ and is equal to $14.73cm-1$. The analysis of the laser spectrum yields the value $(\nu 1+\nu 2)-(3\nu 2)=114.59\pm 0.01cm-1$. Several vibration rotation bands were observed with high resolution in the infrared region. Comparison between an accurate calculated spectrum and the observed one accounts for the structure of the bands and yields the band origins. The origin of $3\nu 3$, for example, is equal to $4054.015cm-1$.