Knowledge Bank

Rotational spectra of the $Ar3-NH3$ and $Ne3-NH3$ van der Waals complexes were measured between 4 and 18 GHz using a pulsed jet Fourier transform microwave spectrometer. The isotopomers studied include those of $NH3$, $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}NH3$, $ND3$, $ND2H$, and $NDH2$ in combination with $Ar3$, $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne3$, $\mathrm{<mrow\; data-mjx-texclass="ORD">22</mrow>}Ne3$, $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne222Ne$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne22Ne2$. The isotopomers containing $Ar3$, $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne3$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">22</mrow>}Ne3$ are symmetric tops for which a-type transitions with $K=3n(n=0,1,2,\dots )$ were observed. The other isotopomers are asymmetric tops and due to the reduced symmetry, all rotational levels are present in these complexes. For $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne222Ne$, both a- and b-type transitions were observed whereas the slightly different mass distribution in $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne222Ne$ led to the detection of a- and c- type transitions. For the deuterium containing isotopomers, each rotational transition is split by the inversion motion of ammonia within the complex. This inverison splitting is not observed in the $NH3$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}NH3$ containing species for spin statistical reasons. The spectroscopic constants, including the $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ nuclear quadrupole coupling constants, were fit for each isotopomer and used to derive structural and dynamical information for the $Ar3-NH3$ and $Ne3-NH3$ van der Waals complexes.