Double charge transfer spectroscopy of acetylene dication C 2H 22+ at vibrational resolution

Abstract

We have observed a vibrational progression of C 2H 2 2+ with double charge transfer (DCT) spectroscopy. From an exploratory calculation, the progression is assigned to the symmetric C–C stretching mode of the lowest singlet 1Δ g state with linear geometry. The observed structure is well reproduced with the theoretical Franck–Condon (FC) factors obtained from the potential curves of the 1Δ g and first-excited 1Σ g + states along the normal C–C stretching coordinate. Multi-reference CI calculations reveal a predominant contribution of the 1Δ g state. These results suggest that the DCT process can probe dicationic states of polyatomic molecules like acetylene with resort to the FC principle.