Knowledge Bank

The high-resolution infrared spectrum of the antisymmetric HCl stretching $\nu 5$ vibrational band in the $(H35Cl)3$ isotopomer of trimer has been measured with a tunable infrared diode-laser supersonic-jet spectrometer. This spectrum of $(H35Cl)3$ was analyzed as the perpendicular band of an oblate symmetric rovibrator. By fitting 527 rovibrational transitions with root-mean-square error of $\pm 0.00054cm-1$ the following molecular parameters were obtained for the trimer: \begin{eqnarray*} &&\nu_{0} C^{\prime} \zeta =2809.77698(6) cm^{-1}, B^{\prime\prime}=6.80414(55)\times 10^{-2} cm^{-1}, B^{\prime}=6.85943(55) \times 10^{-2} cm^{-1},\ &&C^{\prime} - C^{\prime\prime} = 2.737(78) \times 10^{-4} cm^{-1}, D_{JK}{^{\prime\prime}}=-8.40(38) \times 10^{-7} cm^{-1}, D_{JK}{^{\prime}} =-8.14(38) \times 10^{-7} cm^{-1},\ &&D_{J}{^{\prime\prime}} =4.26(16) \times 10^{-7} cm^{-1}, D_{J}{^{\prime}} =4.16(16) \times 10^{-7} cm^{-1}. \ &&D_{K}{^{\prime\prime}}=4.16(22) \times 10^{-7} cm^{-1}.D_{k}^{\prime\prime}=4.32(22)\times10^{-7} cm^{-1}.\end{eqnarray*} A relationship among the centrifugal distortion constants establisher that the geometry of $(H35Cl)3$ is consistent with a dynamically averaged planar ground vibrational state. The centers of mass of the HCl components are separated by 3.693(1) {\AA} in this structure. {Ab initio} methods were also used to estimate the splitting due to the tunneling and experimental evidence indicate that the $(H35Cl)3$ complex has a planar equilibrium structure with no observable tunneling probability between the cw and ccw forms, thus the molecular symmetry of the complex is proposed to be $C3h$(M).