The Rotationally Resolved, Near Infrared Spectrum of the Argon-Methylactylene van der Waals Complex

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Ohio State University

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A molecular beam/optothermal detection technique and F-center laser system have been used to obtain the rotationally resolved, near infrared spectrum of the argon-methylacetylene van der Waals complex in the vicinity of the $v = 1$, C - H stretch of the methylacetylene monomer at 3335 $cm^{-1}$. Of the ca. 140 transitions observed (linewidths 15 - 20 MHz fwhm), 59 have been assigned to an A internal rotor state, b-type spectrum of the complex. These transitions have been fit using a Watson A reduction Hamiltonian in a $I^{1}$ representation. The fit constants for the A state are: $A^{\prime}$ = 0.2910(2) $cm^{-1}$, $B^{\prime} = 0.06109(7)$, $C^{\prime} = 0.05000(4)$, $A^{\prime\prime} = 0.2939(4)$, $B^{\prime\prime} = 0.06127(8)$, $C^{\prime\prime} = 0.04991(6)$, $v_{0} = 3334.5220(5)$ $cm^{-1}$. The A state hand center is red shifted from the monomer band center by 0.5374(8) $cm^{-1}$. A preliminary estimate of the complex’s structure (estimate based on (B + C) / 2 and B - C values of trial structures) has the angle between the symmetry axis of the methylacetylene and a line connecting the triple bond center to the argon at $90^{0}$ and the length of this line as 3.60A.


Author Institution: Department of Chemistry, University of Washington