Spectroscopy of Carbon Vapor Condensed in Rare-Gas Matrices at 4° and 20°K. I

Abstract

The molecules vaporizing from graphite at 2300° to 2600°K have been trapped in neon, argon, and xenon matrices at 4° and 20°K. The near-ultraviolet bands of C3, beginning at 4050 Å in the gas, have been observed in the absorption spectra of these matrices but shifted to 4057 Å in neon, 4102 Å in argon, and 4226 Å in xenon. The neon spectrum is strikingly similar to low-temperature gaseous spectra, including cometary spectra, but the matrix bands occur in groups about 100 cm—1 wide. The infrared spectrum yields a strong band at 2038 cm—1 in argon (2042 cm—1 in neon) which is assigned to v3″, the asymmetric stretching frequency of C3 in the ground electronic state. When the argon matrix is allowed to warm up, diffusion occurs, and larger carbon molecules, C4, C5, C6, etc., are formed, causing the appearance of many new bands in the infrared. The Swan bands of C2 are observed in neon and argon matrices, but only after some annealing of the matrix has occurred by warming. The vibrational frequency of C2 in the excited 3Πu state in a neon matrix is 2094 cm—1, exceeding the value found in any other matrix or in the gas (1750 cm—1). The possible appearance of C2 in its 1Σg+ ground state in neon and argon matrices is briefly discussed.