The Photoelectron Spectrum of Pyrrolide: Nonadiabatic Effects due to Conical Intersections

The negative ion photoelectron spectrum of the pyrrolide-h(4) anion and the completely deuterated analogue, pyrrolide-d(4), are computed employing the multimode vibronic coupling approach, based oil a two-state, fully quadratic, quasi-diabatic Hamiltonian, H-d, which accurately represents the vicinity of the ail initio determined equilibrium geometry of the ground (2)A(2) state as well as the minimum energy crossing point (MECP) oil the symmetry-allowed (2)A(2)-B-2(1) accidental seam of conical intersection. The ab initio data are obtained from multireference configuration interaction wave functions based oil triple-zeta quality atomic orbital bases. The determined photoelectron spectra, which are converged with respect to the vibronic basis, compare favorably with previous spectroscopic results, for pyrrolide-h(4). The principal impact of the seam of conical intersection is a significant perturbation of the portion of the spectrum attributable to the B-2(1) state, in agreement with previous analyses. However. despite the Fact that the MECP is approximately 0.5 eV above the (2)A(2) minimum, its manifestations are shown to be evident in the photoelectron spectrum near threshold. By comparing simulated and measured photoelectron spectrum, it is deduced that the electronic transition moment for the production of the (2)A(2) state of pyrrolyl from pyrrolide is approximately twice that for the production of the B-2(1) state.