Valence and core electron energies in alkyl cadmium compounds from ab initio calculations and photoelectron spectra: Electric field gradients in gas phase Cd compounds

The Hei and x-ray photoelectron spectra of the valence levels, Cd 4d levels, and other core levels in Me₂Cd and Et₂Cd have been recorded. The resolved splitting of the Cd 4d levels is attributed to a ligand field (rather than a bonding) effect, and the major part of the splitting is due to the asymmetric C°₂ crystal field term which transforms like the electric field gradient. The derived C°₂ and C°₄ Ad terms are as follows: Me₂Cd, -0.0225±0.0008 eV and -0.0008±0.0001 eV; Et₂Cd, - 0.023±0.002 eV and -0.0012±0.0004 eV. The photoelectron results are compared with ab initio self-consistent field (SCF) calculations (employing a large Gaussian orbital basis set) for the Cd atom and Me₂Cd complex. The calculation confirms the electrostatic nature of the 4d splitting. In addition, the Cd 4d and C 2s levels both show chemical shifts which are electrostatic in nature, and the Cd 4d: C 2s intensity ratio is in reasonable agreement with that expected if the 4d and 2s orbitals are atomic in nature. Owing to neglect of electronic relaxation, the ground state calculation overestimates both the orbital ionization potentials and the 4d splitting. The calculated value (+20.5 kcal/mole) for the heat of reaction Cd+C ₂H₆→(CH₃)₂Cd is in good agreement with the thermochemical value (+17.7 kcal/mole).