On the molecular structure of uranium dicarbide

ZALAZAR, M. FERNANDA; RAYON, VICTOR M.; LARGO, ANTONIO

Riviera Maya, México

Congreso; XXXVII Congreso de Químicos Teóricos de Expresión Latina -QUITEL 2011; 2011

Solid uranium carbides have received much attention due to their role as appropriate fuels for new generations of nuclear reactors. In particular their thermodynamic properties and crystal structures have been investigated. On the other hand, little is known about uranium carbides in the gas phase, despite vaporization of uranium carbides can occur during their use as nuclear fuels. High-temperature mass spectrometric studies conducted several years ago identified a variety of uranium carbides ranging from UC to UC6. Subsequent experimental work on uranium carbides in the gas phase identified UC2 and UC2+ as some of the most abundant molecular species. In a very recent experimental study Wang et al.1,2 produced uranium-carbon compounds through laser evaporation of uranium-carbon alloys followed by atom reaction in an argon matrix. The analysis of the infrared spectra of the reaction products, together with theoretical calculations, led to the characterization of UC and UC2. According to this combined experimental-theoretical study, UC has a quintet ground state, whereas a linear CUC structure (3Su+ electronic state) with uranium-carbon triple bonds was found for uranium dicarbide1, despite theoretical calculations point to a triangular structure as the most stable species for UC2. The finding of a linear structure for UC2 is in contrast with previous results for second-row3, third-row4 and d-block5 dicarbides, since in these works it was shown that electropositive elements tend to favor triangular ground-state structures. Given the low ionization energy of uranium (6.1941 eV) it should be expected to have a similar behavior. In the present work we report the main results of our theoretical study of the molecular structure of uranium dicarbide, taking into account both linear and non-linear structures as well as different spin multiplicities. Different theoretical methods (DFT, CCSD, CASPT2) have been applied in order to provide information that could be helpful in the interpretation of the experiments. In addition, an analysis of the bonding in the most relevant isomers of uranium dicarbide is also carried out. 1.-           Wang, X.; Andrews, L.; Malmqvist, P.A.; Roos, B.O.; Gonçalves, A.P.; Pereira, C.C.L.; Marçalo, J.; Godart, C.; Villeroy, B. J. Am. Chem. Soc. 2010, 132, 8484. 2.-           Wang, X.; Andrews, L.; D. Ma; Gagliardi, L.; Gonçalves, A.P.; Pereira, C.C.L.; Marçalo, J.; Godart, C.; Villeroy, B. J. Chem. Phys. 2011, 134, 244313. 3.-           Largo, A.; Redondo, P; Barrientos, C. J. Am. Chem. Soc. 2004, 126, 14611. 4.-           Rayon, V.M.; Redondo, P.; Barrientos, C.; Largo, A. J. Chem. Phys. 2010, 133, 124306. 5.-           Rayon, V.M.; Redondo, P.; Barrientos, C.; Largo, A. Chem. Eur. J. 2006, 12, 6963.