A new transient absorption spectrum, attributed to the CCN free radical, has been discovered in the flash photolysis of diazoacetonitrile, HC(CN)N2; three electronic transitions, between 3 500 Å and 4 700 Å, have been photographed for both CC14N and CC15N. The ground state of the radical is a 2Πr electronic state, and the three excited states observed are A2Δ, B2Σ−, and C2Σ+. The 2Π and 2Δ states show evidence of Renner–Teller interaction between the vibrational and electronic angular momenta, an effect not observed previously for 2Δ states. Theoretical expressions for the vibrational energy levels of linear triatomic molecules in 2Δ electronic states have been derived, in terms of a parameter η associated with the quartic terms in the potential energy. They are compared with the observed pattern in the ν2 = 1 level of the A2Δ state. The principal molecular constants for CC14N (in cm−1) are as follows:[Formula: see text]
Attosecond transient absorption spectrum of argon at the
L2,3
edge