Theoretical Study of the Luminescent States and Electronic Spectra of UO2Cl2 in an Argon Matrix

The electronic absorption and emission spectra of free UO2Cl2 and its Ar-coordinated complexes below 27 000 cm(-1) are investigated at the levels of ab initio complete active space second-order perturbation theory (CASPT2) and coupled-cluster singles and doubles and perturbative triples [CCSD(T)] using valence 3 zeta-polarized basis sets. The influence of the argon matrix in the I2K experiment on the electronic spectra is explored by investigating the excited states of argon complexes ArnUO2Cl2. The calculated two most stable complexes with n = 2, 3 can explain the observed two matrix sites corresponding to the experimental two-component luminescence decay. In these uranyl complexes, Ar-coordination is found to have little influence on the (3)Phi (Omega = 2(g)) character of the luminescent state and on the electronic spectral shape. The calculations yield a coherent assignment of the experimental excitation spectra that improves on previous assignments. The simulated luminescence spectral curves based on the calculated spectral parameters of UO2Cl2 from both CASPT2 and CCSD(T) agree well with experiment.