Overtone, 2NH (ν1+ν3) spectroscopy of NH3–Ar and NH3–Kr

Abstract

We have recorded between 6561 and 6671 cm–1 the spectrum of jet-cooled ammonia seeded in Ne, Ar and Kr, using continuous wave cavity ring-down spectroscopy (CW-CRDS). The equivalent absorption pathlength was around 750 m. Three bands are assigned to Π(11)←Σ(00), Π(11)←Π(10) and Δ(?)←Π(10) in the 2NH, ν1+ν3←GS transition of the ortho NH3–Ar dimer. They are rotationally analysed and a simultaneous fitting procedure, together with one far-infrared ground state band from the literature is successfully achieved. A possible Mj-dependent cooling process is reported. Only the first of these bands is observed in the ortho NH3–Kr dimer, and rotationally analysed. Individual line perturbations and anomalous line broadening effects are reported. A J-dependent vibrational predissociation lifetime with a mean value around 0.6 ns is obtained for the Π(11) sub-state in NH3–Ar and NH3–Kr. Two additional bands are assigned to NH3–Ar involving close Π upper sub-states. A group of close bands from the para dimer is identified in NH3–Ar. The energy of all observed ortho and para sub-states is extracted from the analysis. Finally, more bands are reported but their carriers could not be identified.