Reactions of laser-ablated La and Y atoms with CO: Matrix infrared spectra and DFT calculations of the M[(CO).sub.x] and MC[O.sup.+] (M = La, Y; x = 1-4) molecules

Matrix-isolation infrared spectroscopy is used to investigate the reactions of laser-ablated lanthanum and yttrium atoms with carbon monoxide molecules in solid neon. The results have revealed that the C-O stretching vibrational frequencies of MC[O.sup.+] decrease from Sc to La, thus indicating an increase in metal d orbital -> Co [pi]* back-donation in this series.