The photoelectron spectrum of the ethoxide anion: Conical intersections, the spin-orbit interaction, and sequence bands

Abstract

The negative ion photoelectron spectrum of the ethoxide anion (ethoxide-h(5)) and that of its fully deuterated analog, ethoxide-d(5), are calculated using the multimode vibronic coupling approach. A two state quasidiabatic Hamiltonian H(d) is constructed which includes all terms through second order in the full 18 dimensional internal coordinate space. H(d) is centered at the ab initio determined minimum energy crossing (MEX) point on the symmetry-allowed (2)A(")-(2)A(') accidental seam of conical intersection and determined from ab initio energy gradients and derivative couplings. It reproduces the local topography of the (2)A(")-(2)A(') MEX, in addition to accurately representing the geometries, energetics, and harmonic frequencies of equilibrium and saddle point structures located on the ground electronic state potential energy surface in the vicinity of the MEX. Spin-orbit effects are included. The results for ethoxy-h(5) are compared to photoelectron and slow electron velocity-map imaging (SEVI) spectra. By comparing the measured and predicted photoelectron spectrum, the accuracy of the electronic structure treatment is inferred. The existence of sequence bands in the SEVI spectrum is established.