Theoretical studies on structures and electronic spectra of linear HCnN+ (n = 2-14)

► Properties of ground- and excited-states for HCnN+ (n = 2-14) are discussed. ► Odd-n clusters are more stable than even-n analogues with the parity alternation. ► The CASPT2 predicted vertical excitation energies agree well with observed values. ► Notably linear λ-n relationships are found in the (2, 3)2Π ← X2Π transitions.