Knowledge Bank

We previously reported on experimental and theoretical studies of the Xe-N$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ complex as a test case to investigate Xe-molecule interaction potentials.} {\bf WH09}, $59th$ $International$ $Symposium$ $on$ $Molecular$ $Spectroscopy$, $Ohio$ $State$ $University$, $Columbus$, $Ohio$, $USA$, $June$ $21-25$, $2004$.} Here, we present our work on the Xe-CH$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ complex, which is another appealing test case because of the high symmetry of methane monomer and its anticipated near free internal rotation. As a starting point, an $ab$ $initio$ potential energy surface was constructed at the CCSD(T) level of theory. The recently developed aug-cc-pVQZ-PP basis set was used for the xenon atom and the aug-cc-pVTZ basis set for the other atoms. The basis sets were supplemented with bond functions. Dipole moments were also calculated at various configurations. The reliability of the $ab$ $initio$ calculations was tested against the experimental rotational transition frequencies. Rotational transitions were measured using a pulsed-nozzle Fourier transform microwave spectrometer. Transitions within three internal rotation states, namely the $j$=0, $K$=0; $j$=1, $K$=0; and $j$=2, $K$=1 states, were measured and assigned. Nuclear quadrupole hyperfine structures due to the presence of $\mathrm{<mrow\; data-mjx-texclass="ORD">131</mrow>}$Xe ($I$=3/2) were detected and analyzed. It was found that the $j$=1, $K$=0 state is perturbed by a Coriolis interaction with a nearby $j$=1, $K$=1 state. For isotopomers containing CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$D and CHD$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$, the $j$=2 states are no longer metastable and could not be observed. The spectroscopic results were used to derive information about the molecular structure and intermolecular dynamics of the Xe-CH$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ complex.