The ammonia dimer: new infrared-far infrared double resonance results Original Research Article

From the results of an infrared-far infrared double resonance experiment on (NH3)2 complexes in a supersonic slit nozzle expansion, it was possible to characterize the tunneling dynamics, occurring within the ammonia dimer (Havenith et al., Chem. Phys. Letters 193 (1992) 261). In the current paper we present additional infrared-far infrared double resonance spectra. These confirm the former analysis and give a state specific explanation of the overall infrared spectrum of (NH3)2 as measured by Snels et al. (Chem. Phys. 115 (1987) 79). The interchange motion is shown to be quenched from 20 cm−1 in the ground state to less than 1 cm−1 in the infrared excited state. This confirms the assumption of Olthof et al. (J. Mol. Struct. THEOCHEM 307 (1994) 201) that the barrier for interchange tunneling is very small in (NH3)2.