ROTATIONAL SPECTRUM OF $Ar_{2}$-HCN, A VERY FLOPPY T
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Date
1990
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Publisher
Ohio State University
Abstract
The rotational spectrum of $Ar_{2}$-HCN has been observed between 2.5 and 11.5 GHz with a pulsed nozzle. Fourier transform, Balle/Flygare microwave spectrometer. The ground-state rotational constants were determined to be 1769.366, 1743.854, and 857.600 MHz, with b-dipole transitions. The centrifugal distortion, fitted by a Watson Hamiltonian, is extremely large with values for $\tau_{1},\tau_{2}, \tau_{aaaa} \tau_{bbbb}$, and $\tau_{cccc}$ of -6.54, -1.199, -0.68, -0.360, and -0.052 MHz and for $H_{j}$ and $H_{jk}$ or 0.077 and -1.7 KHz. Even with the two 6th order terms the fit has a large ras devlation or 160 KHz. The equilibrium geometry is found to be T-shaped with $C_{2v}$ symmetry and ostensibly planar; however, the inertial defect is $13.9 \mu A^{2}$. extremely large for a planar structure. The N hyperfine interaction depends somewhat on j and K and shows that bending vibrations of the large and highly anisotropic, averaging $^{34}N$ in the plane of the cluster $\theta_{ab}$ and $25^{\circ}$ out-of-plane $\theta_{bc}$. The Ar to HCN center of mass distance is significantly shorter than in Ar-HCN dimer, 4.16 versus A. The unusual properties of the trimer are a more extreme version of those found for the Ar-HCN dimer. As in the case of the latter, they are attributed to the shape of the potential function as calculated with a largely cassical electrical model using low-order moments and multipole $polarizabllitles.^{2}$ The potential surface for $Ar_{2}-HCN$, as a function of $\theta_{ab}$ and $\theta_{bc}$, has a broad elliptical minimum while that for $Ar_{2}-HF$ is steep and more circular. There are similar differences in the dependence on the $Ar_{2} c.m$. to HX o.m. distance.
Description
$^{1}$ T. D. Kiots, C. E. Dykstra, and H. S. Gutowaky, J. Chem. Phys. 90. 30 (1989). $^{2}$ C. E. Dykstra, J. Am. Chem. Soc. 111, 6168 (1989).
Author Institution: Noyes Chemical Laboratory, University of Illinois
Author Institution: Noyes Chemical Laboratory, University of Illinois