Interplay of protection and damage through intermolecular processes in the decay of electronic core holes in microsolvated organic molecules

TL;DR

This study investigates how the environment influences the decay of core holes in microsolvated organic molecules under X-ray irradiation, revealing both protective and damaging effects through experimental and theoretical analysis.

Contribution

It extends understanding of environmental effects on core-hole decay by showing how water molecules can both protect and induce ionization in pyrimidine.

Findings

Environmental protection can be reversed if the core vacancy is in water.

Intermolecular charge transfer can lead to non-dissociative ionization.

Protective effects are complex and depend on the vacancy location.

Abstract

Soft X-ray irradiation of molecules causes electronic core-level vacancies through photoelectronemission. In light elements, such as C, N, or O, which are abundant in the biosphere, these vacancies predominantly decay by Auger emission, leading inevitably to dissociative multiply charged states. It was recently demonstrated that an environment can prevent fragmentation of core-level-ionized small organic molecules through immediate non-local decay of the core hole, dissipating charge and energy to the environment. Here, we present an extended photoelectron-photoion-photoion coincidence (PEPIPICO) study of the biorelevant pyrimidine molecule embedded in a water cluster. It is observed and supported by theoretical calculations that the supposed protective effect of the environment is partially reversed if the vacancy is originally located at a water molecule. In this scenario, intermolecular energy or charge transfer from the core-ionized water environment to the pyrimidine molecule leads to ionization of the latter, however, presumably in non-dissociative cationic states. Our results contribute to a more comprehensive understanding of the complex interplay of protective and harmful effects of an environment in the photochemistry of microsolvated molecules exposed to X-rays.