A theoretical study on the electronic absorption spectrum of nitryl chloride, ClNO2, has been carried out using multi-reference configuration interaction, MRD-CI, methods with cc-pVDZ + sp and cc-pVTZ + sp basis sets. The electronic spectrum is characterized by two very strong transitions (f from 0.30 to 0.67) at 7.04 eV (3(1)A(1) <-- X(1)A(1)) and 7.25 eV (3(1)B(2) <-- X(1)A(1)). Further, the transition at 5.77 eV (2(1)A(1) <-- X(1)A(1)) is predicted to be somewhat less intense (f = 0.02). In addition, the potential energy curves for the ground and low-lying singlet excited states are examined along the Cl-N bond cleavage. Also, triplet excited states of ClNO2 are discussed. (C) 2003 Elsevier B.V. All rights reserved.