Ultrafast energy transfer between water molecules

Abstract

At the transition from the gas to the liquid phase of water, a wealth of new phenomena emerge, which are absent for isolated H 2 O molecules. Many of those are important for the existence of life, for astrophysics and atmospheric science. In particular, the response to electronic excitation changes completely as more degrees of freedom become available. Here we report the direct observation of an ultrafast transfer of energy across the hydrogen bridge in (H 2 O) 2 (a so-called water dimer). This intermolecular coulombic decay leads to an ejection of a low-energy electron from the molecular neighbour of the initially excited molecule. We observe that this decay is faster than the proton transfer that is usually a prominent pathway in the case of electronic excitation of small water clusters and leads to dissociation of the water dimer into two H 2 O , the observed decay channel might contribute as a source of electrons that can cause radiation damage in biological matter.The water molecule is, as a triatomic molecule, rather simple in structure and its geometry is well known. In contrast to that, the interplay of compounds of water molecules or other atoms and molecules with water, for example in a solution, is very rich and far from being fully understood. At the very onset of condensation when two water molecules are combined to form a water dimer a new dimension of complexity arises: electronic excitation of this complex spawns nuclear dynamics leading to fragmentation into a protonated fragment (that is, H 3 O + ) and an OH group 3,4 . For this fragmentation, first a proton migrates from one of the molecules to its neighbour, usually along a distance that is larger than the bond lengths found in the water molecule itself. Such fragmentation dynamics are characteristic for larger clusters, as well 5 . Typical mass spectra of fragments of water droplets show a break-up into protonated cluster fragments (H 2 O) n H + of different sizes and into OH groups. A reason for this is the absence of direct transitions within the Franck-Condon region to break-up channels that do not involve proton migration [6][7][8] . Furthermore, the migration itself is highly efficient and occurs on a timescale of <60 fs (ref. 9).The response of condensed water to electronic excitation has far-reaching consequences for biological systems. Radiation damage to cells naturally depends sensitively on the routes by which energy deposited into the cells is finally distributed and which fragmentation and de-excitation pathways are favoured. Experiments have shown that the constituents of DNA are highly vulnerable to low-energy electrons 1 . These studies revealed that not only does primary ionization by high-energy particles or photons cause damage, but also that low-energy electrons in particular break-up biomolecules efficiently 2 . ). The red oval shows an internuclear distance of 2.9 Å with a corresponding KER of 4.9 eV after the photo reaction. b,c, The process observed in this experiment: an electron from the inner valence shell of one...

On the nature and origin of dicationic, charge-separated species formed in liquid water on X-ray irradiation

“…For inner-valence ionization of the water dimer, the ICD channel is open but sequential double ionization by PTM autoionization has not been identified. 56 We argue that simulations of radiation chemistry processes at the molecular level need to include the mechanisms identified here. Furthermore, we expect that the PTM-Auger and PTM-ICD processes represent a generic feature for hydrogen bonded systems.…”

Site- and energy-selective slow-electron production through intermolecular Coulombic decay

“…We note that only for electrons with energies below 15 eV the microscopic mechanisms for strand breakage have been investigated [10,11,[37][38][39] (for brief discussion on higher energy electrons, see Supplementary Materials). In all the ICD processes during the cascade two or more neighboring ions are produced directly leading to damaging Coulomb explosion [3,40]. The damage to DNA through the ICD electrons and the Coulomb explosion following RA-ICD cascades will happen in the immediate vicinity of the site where the energy was initially deposited.…”

“…It usually proceeds on a femtosecond timescale and becomes faster the more neighbors are present, dominating most of the competing relaxation processes. Experimental investigation of ICD in water dimers [3] found the rate of this process to be so large as to completely suppress the proton transfer in the inner-valence ionized water molecules.As a result of ICD, two intact water cations are produced by the consecutive Coulomb 1 …”

Strong field control of the interatomic Coulombic decay process in quantum dots

“…[1] -this slogan summarizes the nearly twenty years of success history of the ultrafast interatomic (intermolecular) Coulombic decay (ICD) process from its first theoretical prediction by Cederbaum, Zobeley, and Tarantelli [2] to its widespread theoretical and experimental observation [3,4] in various atomic and molecular systems including clusters of noble gas atoms [5,6,7,8], endohedral fullerenes [9,10,11], aqueous solutions [12,13,14,15,16,17], biological systems [18,19,20,21,22,23], and nanomaterials [24,25,26] just to name a few.…”