Generally, it is expected that larger basis sets will predict shorter bond lengths, and our results are consistent with that expectation (Table ). Our MRCI-optimized bond distances and CCSD(T) values agree within 0.02 Å. In terms of experimental references values, the experimental C-O stretching frequency has been reported with co-deposition of laser-ablated hafnium with 0.1% CO in neon at 4-10K. 12 This value 12 is 1869 cm -1 , which differs by 26 from our CCSD(T) value for ).