Knowledge Bank

Microwave and infrared spectra of Ar-HCN have been obtained using an electric-resonance optothermal spectrometer. The microwave measurements extend to higher J the previous results of Leopold $etal.1$ and Klots $etal.2$, allowing the determination of higher-order centrifugal distortion constants for this quasilinear, highly non-rigid complex. A Pad'{e} approximate fit to the microwave data indicates a centrifugal alignment of the HCN subunit with the Ar-HCN axis due to angular-radial coupling. Infrared spectra are reported for the C-H stretching fundamental, $\nu 1$, and the combination band $\nu 1+\nu 5\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$, where $\nu 5$ is the van der Waals bending vibration. The band-origin difference between these two bands gives $\nu 5=-7.8cm-1$, in rough agreement with the $10cm-1$ harmonic value predicted from the microwave-determined nuclear quadrupole coupling constant. The complexation-induced shift of the C-H stretching vibration is $2.69cm-1$ and the vibrational predissociation linewidths. $\Gamma$. are . The vibrationally excited complex predissociates before striking the bolometer detector, implying that the predissociation lifetime, .