Knowledge Bank

Using a pulsed jet Fourier transform microwave spectrometer we have recorded the rotational spectrum of the argon-tropolone van der Waals complex between 6 and 17 GHz. Eighty-six transitions were observed (29 $a$-type and 57 $b$-type) with $J\prime \prime$ values ranging from 2 to 8 and maximum $Ka\prime \prime$ and $Kc\prime \prime$ values of 5 and 8, respectively. The transitions were fit with a Watson A-reduction Hamiltonian in a $Ir$ representation using the SPFIT program} \textbf{60}, 883 (1998).}. The fit ground state constants for argon-tropolone are $A=1080.4365(3)$ MHz, $B=883.4943(3)$ MHz, $C=749.0571(2)$ MHz, $\Delta J=2.591(2)$ kHz, $\Delta JK=-3.32(1)$ kHz, $\Delta K=5.232(9)$ kHz, $\delta J=0.944(1)$ kHz, $\delta K=-0.028(8)$ kHz. The rms error for the transition set in the fit is 4 kHz. When included in the Hamiltonian, the tunneling - rotation interaction term, $F(JaJb+JbJa)$, did not improve the quality of the fit: proton tunneling in the complex appears to be quenched. The argon coordinates in the principal axis system of tropolone monomer are $a=0.43$ \AA, $b=0.23$ \AA, and $c=3.48$ \AA.