An adiabatic potential is constructed for uranyl (UO2)(2+) with inclusion of both harmonic and anharmonic types of charge transfer lattice interactions. Such an approach is used for modeling charge transfer vibronic transitions of uranyl in crystals. It is shown that anomalous hot bands observed in Cs2ZrCl6 : UO2Cl42- are due to a double-well potential of harmonic charge transfer vibronic excitons (CTVE-I) and anharmonic charge transfer vibronic excitons (CTVE-II). In order to explain an uncommon doublet in the absorption spectrum previously reported for UO2Cl42- in Cs2UO2Cl4 crystal, an anharmonic CTVE tunnel model is proposed based on the expected tunneling between CTVE-I and CTVE-II (c) 2007 Elsevier B.V. All rights reserved.