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 M_j-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.

Keywords:

• molecular complex
• ammonia
• CW-CRDS
• overtone spectroscopy
• lifetime

Acknowledgements

We are indebted to Dr I. Kleiner (LISA-Créteil) for kindly and expertly introducing us to some of the ammonia subtleties, to Prof. R.J. Saykally (Berkeley) for useful comments and to Dr J. Loreau (ULB) for useful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1072252.

Additional information

Funding

This work was sponsored by the ‘Wiener-Anspach’ foundation (ACME project) and the Brussels-Capital Region within the program Prospective Research for Brussels (Innoviris).