Structure and Photoelectron Spectrum of Tetramethyldiarsane

Abstract

A systematic theoretical investigation of tetramethyldiarsane is presented to help understand its structure and photoelectron spectrum. Full potential energy curve along the C−As−As−C torsion was calculated at the Hartree−Fock (HF) level, and complete geometry optimizations were performed at HF, second-order Many-Body Perturbation Theory (MBPT(2)), and Coupled-Cluster Singles and Doubles (CCSD) levels of theory. Two conformers, anti and gauche, have been found in accordance with the experimental observations. The calculated geometries are in good agreement with the electron diffraction results. Ionization energies were computed by the Equation-of-Motion Coupled-Cluster (EOM-CC) method. The calculations predict a substantial lone-pair splitting for both conformers which contradicts the original assignment of the photoelectron spectrum by Cowley et al. According to the new assignment, the first and third bands belong to the lone pairs of the anti rotamer, the second band is attributed to the n+ lone-pair co...