Re-visiting the observation of the vibronic sequence of the C2 Swan system

We re-visit the analysis of the Δ v = - 4 vibronic sequence of the C2 Swan system published recently by Yeung et al. [1] in which the heavily perturbed (4,8) band could not be assigned and analyzed satisfactorily. Here, we outline the assignment of 122 transitions of the band by taking into account a recent deperturbation study of the d 3 Π g , v = 4 level by Bornhauser et al. [2]. Improved molecular constants for the a 3 Π u , v = 8 and d 3 Π g , v = 4 states are presented by performing a least-squares fit to the Hamiltonian with a favorable root-mean square error of 0.012 cm−1.