Knowledge Bank

The technique of high power four-level microwave double resonance has been applied to the study of rotational transitions of $NH3$ induced by collisions with the polar molecules $H2O$, $D2O$, NO, CO, $CH3X$, $CX3H$ (X = F, Cl, Br, I) and $CH2CN$. An extremely large collision-induced effect was observed in the $NH3$ --- $H2O$ collision experiment (an order of magnitude larger than that observed in pure $NH3$), and is explained as due to rotational resonance between $NH3\Delta J=\pm 1$ transitions and the far infrared transitions of water. $D2O$ also gave a large effect. The results of the measurements for other collision partners, which are not well understood at the present time, will be discussed. Reciprocity experiments, in which the pumping and signal transitions are reversed, have been carried out for $NH3$ --- rare gas collisions. The selection rules obtained in previous $work1$ have been confirmed but a more extensive mapping of collision-induced transitions has been obtained. Although the signs of corresponding signals are consistent, some of the magnitudes are observed to be quite different. This is explained partly by the principle of detailed balancing and partly by differences in some of the transition probabilities. An attempt is being made to determine the probabilities of individual transitions by combining the results of steady measurements with the direct observation of the recovery time of saturation.