Nonadiabatic nuclear dynamics of the ammonia cation studied by surface hopping classical trajectory calculations

TL;DR

This study applies a surface-hopping classical-trajectory algorithm to model the nonadiabatic nuclear dynamics of ammonia cation, revealing multiple distinct time scales and explaining its nonfluorescent nature.

Contribution

It introduces a Landau--Zener based surface-hopping method for simulating ammonia cation dynamics, aligning well with quantum results and elucidating complex time-dependent behaviors.

Findings

Identified four distinct nuclear dynamic time scales.

Achieved good agreement with quantum simulations for initial 100 fs.

Provided a possible explanation for ammonia cation's nonfluorescence.

Abstract

The Landau--Zener (LZ) type classical-trajectory surface-hopping algorithm is applied to the nonadiabatic nuclear dynamics of the ammonia cation after photoionization of the ground-state neutral molecule to the excited states of the cation. The algorithm employs the recently proposed formula for nonadiabatic LZ transition probabilities derived from the adiabatic potential energy surfaces. The evolution of the populations of the ground state and the two lowest excited adiabatic states is calculated up to 200 fs. The results agree well with quantum simulations available for the first 100 fs based on the same potential energy surfaces. Four different time scales are detected for the nuclear dynamics: Ultrafast Jahn--Teller dynamics between the excited states on a 5 fs time scale; fast transitions between the excited state and the ground state within a time scale of 20 fs; relatively slow partial conversion of a first-excited-state population to the ground state within a time scale of 100 fs; and nearly constant populations after roughly 120 fs due to a dynamical equilibrium between all three states. The latter provides a possible explanation of the experimental evidence that ammonia cation is nonfluorescent.