Nuclear magnetic resonance study of the bonding and diffusion of CO chemisorbed on Pd

Abstract

The authors report use of $^{17}\mathrm{O}$ and $^{13}\mathrm{C}$ NMR to study the bonding of CO on Pd particles. By $^{17}\mathrm{\ensuremath{-}}^{13}$C double resonance, they measure the CO bond length to be 1.20\ifmmode\pm\else\textpm\fi{}0.03 A\r{}. The $^{13}\mathrm{C}$ resonance frequency is exceptionally high, 310 ppm above values typical for metal carbonyls. Evidence that the shift arises from electron-spin polarization is given from studies of the magnitude and the dependence on temperature and frequency of the $^{13}\mathrm{C}$ spin-lattice relaxation time. A diffusion enegy of 6\ifmmode\pm\else\textpm\fi{}2 kcal/mole, half that of CO on Pt, is deduced from motional narrowing of the $^{13}\mathrm{C}$ NMR line.