On the simulation of photoelectron spectra complicated by conical intersections: Higher-order effects and hot bands in the photoelectron spectrum of triazolide (CH)2N3-

We report simulated photoelectron spectra for 1,2,3-triazolide (CH)(2)N-3(-), which reveal the vibronic energy levels of the neutral radical 1,2,3-triazolyl, (CH)(2)N-3. The spectral simulation using a quasidiabatic Hamiltonian H-d comprised of polynomials through 4th order (thereby extending conventional quadratic expansions), is compared to both the experimental spectrum and a standard Franck-Condon (adiabatic) simulation. The quartic H-d is far superior to the quadratic H-d, reproducing the main features of the experimental spectrum and allowing for their subsequent assignment. The contributions from excited anion states successfully reproduce the observed vibronic transitions to the red of the assigned band origin of the neutral species. The algorithmic extensions required for the determination of these hot band contributions to the total spectrum are discussed. Convergence of the spectral envelope with respect to the vibronic basis, including both the principal and hot bands, required more than 109 terms. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3587094]