Effect of Protonation and Deprotonation on Electron Transfer Mediated Decay and Interatomic Coulombic Decay

TL;DR

This study investigates how protonation and deprotonation influence electron transfer decay mechanisms, specifically ICD and ETMD, affecting ionization potentials, decay rates, and relaxation channels in systems like LiH-NH3 and LiH-H2O.

Contribution

It provides new insights into how protonation states modulate non-radiative decay processes and their rates in molecular systems, using advanced computational methods.

Findings

Deprotonation lowers ionization potentials and decay rates.

Protonation increases ionization potentials and can halt decay channels.

Protonation and deprotonation significantly alter decay efficiency.

Abstract

Electronically excited atoms or molecules in an environment are often subject to interatomic/intermolecular Coulombic decay (ICD) and/or electron transfer mediated decay (ETMD) mechanisms. A few of the numerous variables that can impact these non-radiative decay mechanisms include bond distance, the number of nearby atoms or molecules, and the polarisation effect. In this paper, we have studied the effect of protonation and deprotonation on the ionization potential (IP), double ionization potential (DIP), and lifetime (or decay width) of the temporary bound state in these non-radiative decay processes. We have chosen LiH-NH$_3$ and LiH-H$_2$O as test systems. The equation of motion coupled cluster singles and doubles method augmented by complex absorbing potential (CAP-EOM-CCSD) has been used in calculating the energetic position of the decaying state and the system's decay rate. Deprotonation of LiH-NH$_3$/LiH-H$_2$O either from the metal center (LiH) or from ammonia/water lowers the IP and DIP compared to the neutral systems. In contrast, protonation increases these quantities compared to neutral systems. The protonation closes the inner valence state relaxation channels for ICD/ETMD. For example, the decay of the O-2s/N-2s state stops in protonated systems (LiH$_2^+$-H$_2$O, LiH$_2^+$-NH$_3$, and LiH-NH$_4^+$). Our study also shows that the efficiency, i.e., the rate of ICD/ETMD, can be altered by protonation and deprotonation. It is expected to have implications for chemical and biological systems