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

Abstract

The vaporization of C13-substituted carbon has established the isolation of C3 molecules in the matrix and the assignment of the v3″ frequency observed in the infrared spectrum. A vibrational analysis of the near-ultraviolet spectrum (the well-known 4050-Å gas bands) of C3 trapped in a neon or argon matrix has been carried out. The presence of a large Renner effect (ε=+0.566) in the bending motion in the excited state of this 1Πu↔X1Σg+ transition has been confirmed. Infrared and fluorescence spectra also support the assignment of a low bending frequency (∼70 cm—1) in the ground state as recently proposed by Gausset, Herzberg, Lagerqvist, and Rosen. Then the following vibrational frequencies apply: Πu1 state:ν1′=1125 cm−1,ν2′=305 cm−1,ν3′=?;Σg+1 ground state:ν1′′=1235 cm−1,ν2′′≅70 cm−1(?),ν3′′=2040 cm−1.v2″ is still doubtful because it does not yield thermodynamic functions for C3 which agree with those derived by mass spectrometry. The f number (oscillator strength) of the 0–0 band has been found to be about 7×10—4 in a neon matrix. The properties of a long-lived emission (lifetime=0.02 sec in neon) at 5856 Å indicate that it is the 3Πu→1Σg+ transition of C3. Another, rather unpredictable, system of bands near 4200 Å has also been seen in absorption and emission, but the molecule producing these bands has not been identified. An attempt has been made, via a linear chain model, to assign the stretching frequencies of the larger carbon molecules, C4, ···, C12, which have been observed in the infrared after solid-state diffusion was allowed to occur.