Impact of nonadiabatic coupling between the conically intersecting X̃²A<inf>1</inf> and òB<inf>2</inf> states of NO<inf>2</inf> on the negative ion photoelectron spectra of NO^-<inf>2</inf>

Abstract

Negative ion photoelectron spectra of NO-2 at 266 nm (4.660 eV) and 351 nm (3.532 eV) are theoretically calculated and compared with earlier experimental findings. A diabatic model Hamiltonian with linear vibronic coupling between the conically intersecting X̃2A1 and Ã2B2 states of NO2 is employed for this purpose. While the linear vibronic coupling model successfully reproduces the low resolution experimental photoelectron spectrum at 266 nm, second order coupling terms are necessary for the high resolution spectrum at 351 nm. The vibronic structure of the X̃2A1 state of NO2 in the photoelectron spectrum is found to be almost unaffected by the nonadiabatic coupling, whereas, the latter has a strong impact on the vibronic structure of the Ã2B2 state. The magnitude of the vibronic coupling constant, which has otherwise been overestimated by earlier theoretical studies, is calculated ab initio and its limits of validity are confirmed by the results from different ab initio calculations. © 1999 American Institute of Physics.