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 ${}_{}{}^{17}{}_{}{}^{}\mathrm{-}_{}^{13}{}_{}{}^{}$C double resonance, they measure the CO bond length to be 1.20±0.03 Å. 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±2 kcal/mole, half that of CO on Pt, is deduced from motional narrowing of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR line.