Knowledge Bank

“The spectrum of the $C3$ molecule trapped in neon and argon matrices at $4\circ K$ and $20\circ K$ has been studied in absorption in the infrared and near-ultravoilet regions and in fluorescence in the visible region. Many features of the well-known cometary emission spectrum beginning at 4050\AA and strikingly reproduced in the neon absorption spectrum. $C$ substitution has also been used to prove that $C3$ is isolated is isolated under the extreme conditions prevailing during the preparation of the matrices. Analysis of the near-ultraviolet bands yields the excited-state frequencies: $\nu 1=1100cm-1,\nu 2\prime =420cm-1,\nu 3\prime =?$. Fluorescence and infrared measurements give the ground-state frequencies: $\nu 1″=1235cm-1\nu 3″=2042cm-1$. Our ultraviolet spectra are in accord with the low bending frequency, $\nu 2″\cong 70cm-1$, recently proposed by Gausset, Herzberg, Lagerquist, and $Rosen.1$ Other complexities in the spectrum indicate that the observed transition may be $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi u⟷X3\Sigma g-$- rather than the expected $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u⟷\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$. A similar study has been made of the $SiC2$ molecule which has been observed in stellar spectra and produced in the laboratory by $Kleman2$. The matrices have been prepared by trapping the vapour effused from hot silicon carbide. The absorption spectrum in a neon matrix begins at 4963{\AA} (as compared to 4977{\AA} in the gas) and contains some weak bands not observed by Kleman. The matrix may also exhibit the spectra of the $Si2,Si2C$, and $Si2C3$ molecules, depending upon the conditions of vaporization. “