The electronic structure of TEMPO, its cation and anion

Abstract

The electronic structure of TEMPO (2,2,6,6-Tetramethylpiperidine-N-oxyl) and its cation and anion were studied experimentally using the electron spectroscopy techniques, dissociative electron attachment (DEA) spectroscopy, electron energy-loss spectroscopy, measurement of elastic and vibrational excitation (VE) cross sections and HeI photoelectron spectroscopy. The experiments were supplemented by quantum-chemical calculations of excitation energies, ionisation potential and the Franck–Condon profile of the first photoelectron band. Electron energy-loss spectra were recorded up to 12 eV and revealed a number of bands that were assigned to two valence and a number of Rydberg transitions. VE cross sections reveal a broad band in the 3–12 eV range, assigned to σ* shape resonances and signals in the 0–1 eV range, assigned to a shape resonance corresponding to a temporary capture of the incident electron in the (already singly occupied) π* orbital. Narrow threshold peaks in the VE cross sections are assigned to dipole-bound resonances. The major DEA fragment was found to be O−, with bands at 5.0 and 6.87 eV, assigned to core excited resonances.