Knowledge Bank

Weak transitions of the type $ \Delta K_{a} =\pm 2$ in $D2CO$ have been observed by the microwave double resonance method. In this three level system, the effect of pumping on the weak transition is registered by the change in intensity of the monitored line. Several transitions in $D_{2}CO $ are sufficiently strong to be seen by direct absorption using Stark modulation. Lines with change in $ K_{a} = (0 {\rightarrow} 2)$, $(1\to 3)$ and $(3\to 1)$ have been measured and assigned. Refined values of the molecular constants and some interesting features of such transitions will be discussed. Extension of this work to $H2CO$ is underway.