Photoionization-induced dynamics of ammonia: Ab initio potential energy surfaces and time-dependent wave packet calculations for the ammonia cation

Abstract

An analytical anharmonic six-dimensional three-sheeted potential energy surface for the ground and first excited states of the ammonia cation has been developed which is tailored to model the ultrafast photoinduced dynamics. Selected ab initio cuts, obtained by multireference configuration interaction calculations, have been used to determine the parameters of a diabatic representation for this Jahn-Teller and pseudo-Jahn-Teller system. The model includes higher-order coupling terms both for the Jahn-Teller and for the pseudo-Jahn-Teller matrix elements. The relaxation to the ground state is possible via dynamical pseudo-Jahn-Teller couplings involving the asymmetric bending and stretching coordinates. The photoelectron spectrum of NH3 and the internal conversion dynamics of NH3+ have been determined by wave packet propagation calculations employing the multiconfigurational time-dependent Hartree method. Three different time scales are found in the dynamics calculations for the second absorption band. The ultrafast Jahn-Teller dynamics of the two excited states occurs on a 5 fs time scale. The major part of the internal conversion to the ground state takes place within a short time scale of 20 fs. This fast internal conversion is, however, incomplete and the remaining excited state population does not decay completely even within 100 fs.

Global Analytical Potential Energy Surfaces for High‐resolution Molecular Spectroscopy and Reaction Dynamics

“…Nangia and Truhlar (2006) and Li et al (2007) derive a two-sheet analytical representation of the lowest adiabatic electronic states of ammonia from a direct calculation of diabatic states. Viel et al (2006) present a three-sheet analytical representation for the ammonia cation from a different diabatization ansatz. Very little is known, however, about the spectroscopic accuracy of these representations.…”

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

“…26 However, in the 1,2,3-triazolyl radical, the complicated topographical features noted above precluded the construction of a uniformly accurate quadratic H d . These limitations of the fully quadratic model clearly illustrated the benefits that can be obtained from incorporating higher-order terms in the expansion of H d , as has been noted by others [27][28][29] for highly symmetric molecules exhibiting conical intersections.…”

Jahn–Teller and spin–orbit coupling effects in transition-metal trifluorides

“…In principle, a two-mode JT + PJT model Hamiltonian can be derived by an expansion up to sixth or higher-order, which provides an accurate description of the (E ′ + A ′ 1 ) × (e ′ + e ′ ) three-state conical intersection problem. 74,89 The analysis of the PJT effect and its dynamic consequences (radiationless decay of the 4 E ′ excited state to the 4 A ′ 1 ground state) is, however, beyond the scope of the present work. …”