Spectroscopy of Silicon Carbide and Silicon Vapors Trapped in Neon and Argon Matrices at 4° and 20°K

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Abstract
The numerous molecules vaporizing from silicon carbide at 2600°K and from silicon at 2300°K have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near‐ultraviolet regions. The Si2 and SiC2 molecules have been observed, and less definitely, also Si2C, Si2C3, Si3, and Si4. In the case of silicon carbide vaporization, the absorption spectrum of SiC2 appears strongly at 4963 Å in neon and 4993 Å in argon as compared with 4977 Å in the gas. The spectrum agrees with the gaseous observations of McKellar and Kleman, but with the addition of three weak but distinct bands. It is interpreted as a 1Πu←X1Σ+ transition where the vibrational assignments in these states are now as follows: 1Σ+, ν1″=853, ν2″=300, ν3″=1742 cm—1; 1Π, ν1′=1015, ν2′=230, ν3′=1461 cm—1. The vibrational structure in the upper state is anomalous in that it requires a large positive value for x13′. The spectrum of symmetrical Si2C is believed to occur at 5300 Å in argon with ν1′=500 cm—1. An extensive absorption spectrum between 6500 Å and 5300 Å is attributed to Si2C3 and has been partially analyzed. The infrared spectra of these matrices confirm the ground state frequencies of SiC2 and lead to a tentative assignment of the Si2C3 frequencies. In the case of silicon vaporization, 17 vibrational levels in the upper state of the 3Σu—←X3Σg— transition of Si2 at 4000 Å, formerly seen in the gas by Douglas and by Verma and Warsop, have been observed. Two other weak systems of bands at 4660 and 5700 Å have been tentatively attributed to Si3 and Si4, respectively. Other regularities in the carbon, silicon, and silicon—carbon molecular series are discussed.