Direct observation of inversion transitions in the v=5 state of NH3 by millimeter wave‐optical double resonance

A powerful method for detailed studies of the static and dynamic properties of molecules in highly excited vibrational states is presented. NH3 molecule is excited to the v=5 state in the N–H stretching mode by a pulsed dye laser and a subsequent transient change in the millimeter wave absorption due to the inversion transition in the excited state is observed before the distribution returns to thermal equilibrium. The determined inversion transition frequencies are more accurate by more than two digits than those reported in the previous work.