Laser evaporation of carbon rich uraniumcarbon alloy targets into condensing argon or neon matrix samples gives weak infrared absorptions that increase on annealing, which can be assigned to new uranium carbon bearing species. New bands at 827.6 cm-1 in solid argon or 871.7 cm -1 in neon become doublets with mixed carbon 12 and 13 isotopes and exhibit the 1.0381 carbon isotopic frequency ratio for the UC diatomic molecule. Another new band at 891.4 cm-1 in argon gives a three-band mixed isotopic spectrum with the 1.0366 carbon isotopic frequency ratio, which is characteristic of the anti-symmetric stretching vibration of a linear CUC molecule. No evidence was found for the lower energy cyclic U(CC) isomer. Other bands at 798.6 and 544.0 cm-1 are identified as UCH, which has a uranium-carbon triple bond similar to that in UC. Evidence is found for bicyclic U(CC)2 and tricyclic U(CC)3. This work shows that U and C atoms react spontaneously to form the uranium carbide UC and CUC molecules with uranium-carbon triple bonds.
Bibliographical noteFunding Information:
We gratefully acknowledge financial support from (U.S.) Department of Energy (DOE) Grants Nos. DE-SC0001034 and DE-SC002183, NCSA computing Grant No. CHE07-0004N, and the Fundação para a Ciência e a Tecnologia through the Ciência 2007 Program. D.M. thanks the UMN MRSEC for financial support.