The A (1)Pi((u)) <- X (1)Sigma(+)((g)) electronic transition of CCN+ and CNC+

The electronic absorption spectra of the A (1)Pi ((0)) <-- (1)Sigma (+)((g) ) transition of CCN+ and CNC+ have been observed in a 5 K Ne matrix after m ass selection of C2N-. CCN- has the origin band at 462.0(2) nm. The vibrati onal structure with frequencies 1223(20) and 1725(20) cm(-1) corresponds to the symmetric and antisymmetric stretching modes in the excited state. The origin band of CNC- is observed at 325.7(2) nm, and the system shows exten sive vibrational excitation. Calculations of the potential energy functions of CCN+ and CNC- in their X 1 Sigma (+)((g)) ground state and the A (1)Pi state of CCN+ followed by variational evaluation of the rovibronic energy l evels allows the assignment of the observed spectra. These spectroscopic da ta open the way to gas-phase studies of the astrophysically important C2Nions.