We present a model for Desorption Induce by (Multiple) Electronic Transitions (DIET/DIMET) based on potential energy surfaces calculated with the Delta Self-Consistent Field extension of Density Functional Theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on various transition metal surfaces, and show that classical nuclear dynamics does not suffice for propagation in the excited state. We present a simple Hamiltonian describing the system, with parameters obtained from the excited state potential energy surface, and show that this model can describe desorption dynamics in both the DIET and DIMET regime, and reproduce the power law behavior observed experimentally. We observe that the internal stretch degree of freedom in the molecules is crucial for the energy transfer between the hot electrons and the molecule when the coupling to the surface is strong.
Core-excitation of water ice releases many different molecules and ions in the gas phase. Studying these desorbed species and the underlying mechanisms can provide useful information on the effects of X-ray irradiation in ice. We report a detailed study of the X-ray induced desorption of a number of neutral, cationic and anionic species from amorphous solid water. We discuss the desorption mechanisms, and the relative contributions of Auger and secondary electrons (X-ray induced Electron Stimulated Desorption) and initial excitation (\rev{direct desorption}) as well as the role of photochemist…
This work proposes a new photophysical phenomenon whereby UV/vis excitation of a molecule involving a Franck-Condon (FC) active vibration yields infrared (IR) emission by strong coupling to an optical cavity. The resulting UV/vis-to-IR photonic down conversion process is mediated by vibrational polaritons in the electronic excited state potential. It is shown that the formation of such excited state vibrational polaritons (ESVP) via UV/vis excitation only occurs with molecules having vibrational modes with both a non-zero FC activity and IR activity in the excited state. Density functional the…
It is found out that there are physical effects, typical of small metal clusters deposited on a non-adsorbing support, that cause a difference between the adsorption properties of sites at the metal cluster surface and those of sites at the boundary of metal-support. This difference gives rise to an extra band in the IR spectra of the adsorbate whose major property is that its intensity changes with cluster size. The migration of chemisorbed molecules (atoms, ions) and molecules (atoms, ions) in any excited state over adsorption sites of different type results in changes in the state of the mo…
Context. Methane is among the main components of the ice mantles of insterstellar dust grains, where it is at the start of a rich solid-phase chemical network. Quantification of the photon-induced desorption yield of these frozen molecules and understanding of the underlying processes is necessary to accurately model the observations and the chemical evolution of various regions of the interstellar medium. Aims. This study aims at experimentally determining absolute photodesorption yields for the CH4 molecule as a function of photon energy. The influence of the ice composition is also investig…
The distinctive set of infrared (IR) emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3μm are ubiquitously seen in a wide variety of astrophysical environments. They are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. However, not a single PAH species has yet been identified in space, as the mid-IR vibrational bands are mostly representative of functional groups and thus do not allow one to fingerprint individual PAH molecules. In contrast, the far-IR (FIR) bands are sensitive to the skeletal characteristics of a molecule, hence they are important for chemical identificati…
Aqueous proton transport at interfaces is ubiquitous and crucial for a number of fields, ranging from cellular transport and signaling, to catalysis and membrane science. However, due to their light mass, small size and high chemical reactivity, uncovering single proton surface transport at room temperature and in aqueous environment has so far remained out-of-reach of conventional atomic-scale surface science techniques, such as STM. Here, we use single-molecule localization microscopy techniques to resolve optically the transport of individual excess protons at the interface of hexagonal bor…
The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of -NH- to -N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C-H bon…
An explanation is provided for the ultrafast photo-excited electron dynamics in low-spin Ruthenium (II) organic complexes. The experimentally-observed singlet to triplet decay in the metal-to-ligand charge-transfer (MLCT) states contradicts the expectation that the system should oscillate between the singlet and triplet states in the presence of a large spin-orbit coupling and the absence of a significance change in metal-ligand bond length. This dilemma is solved with a novel quantum decay mechanism that causes a singlet to triplet decay in about 300 femtoseconds. The decay is mediated by the…
In order to study electron-transfer mediated chemical processes on a metal surface, one requires not one but two potential energy surfaces (one ground state and one excited state) as in Marcus theory. In this letter, we report that a novel, dynamically-weighted, state-averaged constrained CASSCF(2,2) (DW-SA-cCASSCF(2,2)) can produce such surfaces for the Anderson Impurity model. Both ground and excited state potentials are smooth, they incorporate states with a charge transfer character, and the accuracy of the ground state surface can be verified for some model problems by renormalization gro…
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 p…
Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented for the first time and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained earlier for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorpho…
