The longitudinal relaxation timeT1 and the transverse relaxation timeT3 for the inversion levels of the NH3 molecule have been calculated for NH3 — NH3, NH3 — N2 and NH3 — H2 collisions. The ratioT2/T1 lies between 1 and 2 which agrees well with the experiment. The phase shift effect onT2 and on the collisioninduced line shift δω under the framework of the Mehrotra-Boggs theory have also been evaluated. The change in the line intensity ΔI/I, in four-level double resonance experiments was also calculated, and the significance of higher order interaction terms has been pointed out.
