High Resolution Gas Phase Photoelectron Spectra of CoredLevels Using He II Radiation

Abstract

Using a newly constructed charged particle oscillator He II discharge lamp, we have obtained high resolution (≤0.03 eV instrumental resolution) spectra of the outermost metal core d levels in alkyl compounds of Cd, In, and Pb. The Cd and In 4d spectra of Me₂Cd (Me = CH₃), Et₂Cd (Et = C₂H₅) and Me₃In are split into five peaks due to the combined effects of spin orbit splitting (5/2 λ) and an asymmetric crystal field (the C₂⁰ term which transforms like the electric field gradient). As expected, the spin orbit split Pb 5d levels in the tetrahedral molecule Et₄Pb (C₂⁰ = 0) show no noticeable crystal field splitting. The new photoelectron effect enables electric field gradients to be obtained in the gas phase. Our derived C₂⁰ values are consistent with previously measured nuclear electric field gradients in Cd and In compounds; and the measured C₂⁰ value for Me₂Cd is in qualitative agreement with that calculated by H. Basch from an ab initio self-consistent field (SCF) calculation. Because the measured linewidths are mainly due to the inherent natural linewidths of the d levels, we can readily obtain natural d widths from these spectra. The high resolution spectra of the Cd 4d levels of Et₂Cd enable us to resolve Cd 4d peaks due to Cd atoms and EtCd radicals. The Cd 4d spectra of Me₂Cd and Et₂Cd taken at 21.2 eV, 40.8 eV, and 51.0 eV photon energies show marked changes in the relative intensities of the five 4d peaks.