Vibrational spectra of cyclic C6 in solid argon

Vapors from solid and powdered carbon emitted from an oven cycled between 2000 and 3000 K were co-condensed with argon onto a CsI substrate maintained at 10 K. The cycling process produced a matrix “sandwich” with regions of high carbon density alternating with layers of argon. FTIR measurements including extensive 13C isotopic data, supported by ab initio calculations, allow the assignment of a band at 1694.7 cm−1 to the ν4(e′) fundamental of cyclic C6. This represents the first conclusive identification of a small cyclic neutral polycarbon. Additionally, a vibration previously observed at 1710.3 cm−1 has been confirmed as the ν9(σu) mode of linear C8.