Emission spectrum of mass-selected C4−:C2Πu → X2Πg in a neon matrix

The laser excited emission spectrum of the C2Πu → X2Πg electronic transition of mass-selected C4− embedded in a 5 K neon matrix has been observed. This is an extension of the technique coupling mass spectrometry and matrix isolation and allows information on the vibrational frequencies of the species in the ground state to be obtained. In the case of C4−, three vibrational frequencies (ν1(σg+) = 2047(20), ν2(σg+) = 936(20) and ν4(πg) = 396(20) cm−1) have been inferred for the X2Πg state.