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

TL;DR

This study explores how water clusters protect or damage organic molecules when exposed to X-rays by transferring energy and charge.

Contribution

The paper reveals that water can both protect and harm organic molecules through intermolecular energy and charge transfer.

Findings

Water clusters can prevent fragmentation of core-ionized organic molecules through non-local decay.

When the core hole is in water, energy and charge transfer to the organic molecule can cause its ionization.

The protective and harmful effects of the environment depend on the location of the core hole.

Abstract

Soft X-ray irradiation of molecules causes electronic core-level vacancies through photoelectron emission. 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-ionised 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-ionised water environment to the pyrimidine molecule leads to ionisation 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.

Intermolecular energy and charge transfer from inner-shell-ionised water towards neighboring organic molecules is investigated.

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