Ammonia dimer: extremely fluxional but still hydrogen bonded

Author(s)Aling, Jing
Author(s)Szalewicz, Krzysztof
Author(s)van der Avoird, Ad
Date Accessioned2022-04-20T19:57:22Z
Date Available2022-04-20T19:57:22Z
Publication Date2022-03-18
DescriptionThis article was originally published in Nature Communications. The version of record is available at:
AbstractIn the 1980s, Nelson, Fraser, and Klemperer (NFK) published an experimentally derived structure of the ammonia dimer dramatically different from the structure determined computationally, which led these authors to the question “Does ammonia hydrogen bond?". This question has not yet been answered satisfactorily. To answer it, we have developed an ab initio potential energy surface (PES) for this dimer at the limits of the current computational capabilities and performed essentially exact six-dimensional calculations of the vibration-rotation-tunneling (VRT) spectra of NH3-NH3 and ND3-ND3, obtaining an unprecedented agreement with experimental spectra. In agreement with other recent electronic structure calculations, the global minimum on the PES is in a substantially bent hydrogen-bonded configuration. Since the bottom of the PES is exceptionally flat, the dimer is extremely fluxional and the probability of finding it in configurations that are not hydrogen bonded is high. Nevertheless, the probability of hydrogen-bonded configurations is large enough to consider the ammonia dimer to be hydrogen bonded. We also show that NFK’s inference that the ammonia dimer is nearly rigid actually results from unusual cancellations between quantum effects that generate differences in spectra of different isotopologues.en_US
SponsorThis research was supported by NSF grant CHE-1900551 (K.S.). We thank Claude Leforestier for making his computer program available to us.en_US
CitationJing, A., Szalewicz, K. & van der Avoird, A. Ammonia dimer: extremely fluxional but still hydrogen bonded. Nat Commun 13, 1470 (2022).
PublisherNature Communicationsen_US
TitleAmmonia dimer: extremely fluxional but still hydrogen bondeden_US
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