THE ROTATIONAL SPECTRUM AND STRUCTURE OF $Si_{3}$
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Date
2003
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Ohio State University
Abstract
The rotational spectrum of a pure silicon cluster, the $Si_{3}$ trimer, has been observed for the first time. From the rotational constants of the normal and the $^{29}Si$ and $^{30}Si$ isotopic species, a precise geometrical structure has been derived: the trimer is an isosceles triangle with a bond to the apex Si of length 2.165(7) {\AA} and an apex angle of $78.1(4)^{\circ}$. The substantial inertial defect and fairly large centrifugal distortion suggest that the molecule possesses a shallow bending potential. $Si_{3}$ is a good candidate for astronomical detection because radio lines of comparably massive silicon molecules (e.g., $SiC_{2}, SiC_{4}$, and SiS) are readily observed in at least one astronomical source: the circumstellar shell of $IRC+10216$. In excess of $10_{13}$ silicon trimers are produced per gas pulse in our molecular beam, implying that the rotational spectra of $Si_{6}, Si_{9}$, and even larger polar silicon clusters may be detectable with the present technique, as well as similar germanium clusters.
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Author Institution: Harvard-Smithsonian Center for Astrophysics; Division of Engineering and Applied Sciences, Harvard University