This dissertation elucidates the instrumentation and application of a hybrid ambient ionization source, laser electrospray mass spectrometry (LEMS), for the direct analysis and molecular imaging of biological tissue without matrix deposition. In LEMS, laser pulses from a Ti:Sapphire laser amplifier (60 fs, 800 nm, and 1 mJ) interact with surface analytes and transfer them from the condensed phase into the gas phase without the requirement of either exogenous matrix or endogenous water in the sample. The laser vaporized analytes are captured and ionized by an electrospray source, and finally detected by a mass analyzer. It was found that a turn-key, robust femtosecond fiber laser with longer wavelength, longer duration, and lower pulse energy at 1042 nm, 425 fs, and 50 µJ, respectively, provided comparable results with the Ti:Sapphire laser. Vaporization of intact, dried or aqueous cytochrome c and lysozyme samples was demonstrated by the fiber laser. A charge states distribution at lower charge states indicating folded conformation of proteins and the hemoglobin α subunit-heme complex from whole blood was observed. Endogenous anthocyanins, sugars, and other metabolites were detected and revealed the anticipated metabolite profile for the flower petal and leaf samples by the fiber laser. Phospholipids, especially phosphatidylcholine, were identified from a fresh mouse brain section sample. These lipid features were suppressed in both the fiber laser and Ti:Sapphire LEMS measurement in the presence of optimal cutting temperature compounds which are commonly used in animal tissue cryosectioning. This dissertation also details the design of an automated mass spectrometry imaging source based on the Ti:Sapphire LEMS. The laser, translation stage, and mass analyzer are synchronized and controlled using a customized user interface to enable step-by-step scanning of the area of interest on a given tissue sample. The imaging source is coupled with a high resolution accurate mass quadrupole time-of-flight (QTOF) mass analyzer with tandem mass analysis capability. A lateral resolution of 60 µm was demonstrated on a patterned ink film by LEMS imaging. Plant metabolites including sugar and anthocyanins were directly imaged from a leaf sample. Small metabolites, lipids and proteins were simultaneously imaged from a single tissue section of a pig liver sample. Biomarkers of blood-brain barrier damage and traumatic brain injury (TBI) that occurred during the injury were detected and imaged from a TBI mouse brain. The loading values from principal component analysis (PCA) were shown to be useful for identification of features of interest from the large LEMS imaging dataset. / Chemistry

Spaceborne impact ionization mass spectrometers, such as the Cosmic Dust Analyzer on board the past Cassini spacecraft or the SUrface Dust Analyzer being built for NASA's upcoming Europa Clipper mission, are of crucial importance for the exploration of icy moons in the Solar System, such as Saturn's moon Enceladus or Jupiter's moon Europa. For the interpretation of data produced by these instruments, analogue experiments on Earth are essential. To date, thousands of laboratory mass spectra have been recorded with an analogue experiment for impact ionization mass spectrometers. Simulation of mass spectra of ice grains in space is achieved by a Laser Induced Liquid Beam Ion Desorption (LILBID) approach. The desorbed cations or anions are analyzed in a time-of-flight mass spectrometer. The amount of unstructured raw data is increasingly challenging to sort, process, interpret and compare with data from space. Thus far this has been achieved manually for individual mass spectra because no database containing the recorded reference spectra was available. Here we describe the development of a comprehensive, extendable database containing cation and anion mass spectra from the laboratory LILBID facility. The database is based on a Relational Database Management System with a web server interface and enables filtering of the laboratory data using a wide range of parameters. The mass spectra can be compared not only with data from past and future space missions but also mass spectral data generated by other, terrestrial, techniques. The validated and approved subset of the database is available for general public (https://lilbid-db.planet.fu-berlin.de).

No / The use of matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry on intact cell microorganisms, Intact Cell MALDI (ICM), has been shown by numerous workers to yield effective species level identification. Early work highlighted the significant effect that variation in culture media, incubation conditions and length of incubation had on the spectra produced. Therefore, in order to achieve reliable and reproducible species level identification and sub-typing of microorganisms from ICM fingerprints, it has been essential to develop standardised methods. For methicillin-resistant Staphylococcus aureus (MRSA), a major nosocomial pathogen, we have developed such a standardised method. In this paper we present the experimental parameters, namely, the incubation period, the number of passages required from lyophilised or stored isolates, the method of deposition of the bacterial cells, the concentration of matrix solution, the drying time of bacterial cells prior to the addition of the matrix solution, the time between preparation of the bacterial/matrix sample and analysis and the MALDI pulsed extraction setting, which were considered during the development of defined methods.

This thesis describes the design, construction and optimisation of two compact setups to produce ⁸⁷Rb Bose-Einstein condensates and dual ⁷Li-⁸⁷Rb Magneto- Optical Traps (MOTs). The motivation for compact systems is to have simplified systems to cool the atoms. The first experimental setup is based on a single pyrex glass cell without the need for atom chips. Fast evaporation will be achieved in a hybrid trap comprising of a magnetic quadrupole trap and an optical dipole trap created by a Nd:YVO4 laser and with future plans of using a Spatial Light Modulator (SLM). To enhance an efficient and rapid evaporation, we have investigated Light-Induced Atomic Desorption (LIAD) to modulate the Rb partial pressure during the cooling and trapping stage. With this technique, a ⁸⁷Rb MOT of 7 x 10⁷ atoms was loaded by shining violet light from a LED source into the glass cell, whose walls are coated with rubidium atoms. The atoms were then cooled by optical molasses and then loaded into a magnetic trap where lifetime measurements demonstrated that LIAD improves on magnetically-trapped atoms loaded from constant background pressure by a factor of six. This is quite encouraging and opens the possibility to do a rapid evaporation. In a second experiment, we have designed a compact system based on a stainless steel chamber to trap either ⁷Li or ⁶Li atoms in a MOT loaded from alkali-metal dispensers without the need of conventional oven-Zeeman slower. This setup can also load ⁸⁷Rb atoms, allowing future projects to simultaneously produce degenerate quantum gases of bosonic ⁸⁷Rb and fermionic ⁶Li atoms.

This Thesis contains details of the construction and characterisation of a compact apparatus for the cooling of ultracold atoms to quantum degeneracy, and their manipulation in flexible holographic optical traps. We have designed and built two iterations of this apparatus. The first version consists of a stainless steel single-cell vacuum chamber, in which we confine ⁸⁷Rb and ⁶Li or ⁷Li in a Magneto-Optical Trap. We characterise the alternative methods of pulsed atomic dispenser and Light Induced Atomic Desorption (LIAD) to rapidly vary the background pressure in the vacuum chamber with the view to enabling efficient evaporative cooling in the single chamber, loading MOTs of up to 10⁸ atoms using pulsed dispensers. The LIAD is found to be ineffective in loading large MOTs in this setup, while the pulsed dispensers method gradually increases the background pressure in the chamber over time. Based on the results of this first iteration, we designed and built a second single-chamber apparatus for cooling of ⁸⁷Rb to quantum degeneracy. The LIAD technique was used to successfully load MOTs containing 8x10⁷ atoms in this single pyrex cell with a rapidly-varying background pressure. The lifetime of an atomic cloud loaded from the MOT into a magnetic trap increased by a factor of 6 when LIAD was used. The holographic optical traps for cold atoms are generated using a Spatial Light Modulator, and we present our novel method for improving the quality of holographic light patterns to the point where they are suitable for trapping ultracold atoms using a feedback algorithm. As demonstrations of this new capability, we show power-law optical traps which provide an efficient, reversible route to Bose-Einstein Condensation and a dynamic ring trap for the investigation of superfluidity in cold atoms.

Dans ce travail nous avons étudié des réactions chimiques sur la surface de deux métaux : le platine et l'or, en utilisant la microscopie ionique à effet de champ électrique (FIM) et la spectrométrie de masse de désorption par champ pulsé (PFDMS). En complément de ces données expérimentales, nous apportons des résultats obtenus par la théorie de la fonctionnelle de la densité (DFT). La taille et la morphologie de nos échantillons font qu’ils sont de bons modèles de grains de phase active dans un catalyseur réel. Sur le platine nous avons observé l'interaction du monoxyde d'azote. En présence d'un champ électrique, la dissociation du NO est promue, laissant sur la pointe une couche d'oxygène que l'on peut titrer par la suite avec du NO pour former du dioxyde d'azote. L'interaction de l'hydrogène avec une pointe de platine est différente en fonction de la température. A basse température (<200 K), l’hydrogène met en image la pointe avec un assombrissement de petites régions de la pointe. A partir de 200 K, l'hydrogène induit une transformation de la pointe : les faces denses s'élargissent au détriment des faces rugueuses, avec une rangée d'atomes le long des lignes de zone [100] et le pôle central passe d’une forme circulaire à une forme carrée. L'hydrogène est supposé être à l'état atomique sur la surface; sous sa forme moléculaire, il ne contribue qu'à la mise en image. C’est sous sa forme atomique qu’il contribue aux transformations observées. La réaction NO+H2 sur le platine conduit à l'observation d'instabilités cinétiques pour des pressions et températures données. Les régions d'amorçage ont été identifiées comme étant tout ensemble de sites de cran situé le long des lignes de zone [100]. L'observation de phénomènes oscillants n'est pas liée exclusivement à une morphologie de type polyédrique : il est possible d’observer ces instabilités cinétiques sur des pointes de rayon de courbure différent, ces pointes ne subissent pas nécessairement un changement de morphologie. L'analyse chimique au cours de la réaction a révélé la présence d'oxydes de surface ce qui nous a conduit à penser que la surface du catalyseur de platine doit être oxydée plutôt que de rester à l'état métallique. Une étape intermédiaire dans le mécanisme de site vacant a été proposée pour permettre de rendre compte de l'apparition de phénomènes oscillants. L’étape déterminante est la décomposition du monoxyde d’azote adsorbé à la surface. L’apport d’hydrogène atomique nécessaire à la formation d’eau n’est pas une étape lente, au contraire l’hydrogène semble être largement présent sous forme atomique. L’influence du champ électrique reste important, ce qui pourrait expliquer les différences de gammes de température auxquelles d’autres groupes et le nôtre observons des oscillations. L'étude de l'interaction du CO seul sur l'or a été motivée par l'observation de la réaction CO+O2 sur pointe d'or. Sous nos conditions expérimentales, il est possible de former des mono- et dicarbonyles d’or sous forme cationique. En présence d'un champ électrique, la formation de carbonyles d'or est promue au niveau des sites de cran de la surface. Les résultats obtenus par DFT sont concordants avec les résultats expérimentaux. A l'instar du Pt, nous avons étudié l'interaction du monoxyde d'azote sur pointe d'or. Nous avons observé la formation de protoxyde d'azote et d'un dimère de monoxyde d'azote. Le mécanisme de formation de ces espèces reste encore inconnu. Une couche d'oxygène adsorbée à la surface peut être titrée par du NO en formant du dioxyde d'azote. En présence d'oxygène seul sur une pointe d'or sans champ électrique, les spectres de masse ne révèlent que la présence d'oxygène moléculaire. En présence d'un champ électrique, il est possible de détecter de l'oxygène atomique sans toutefois avoir la formation d'un oxyde d'or. Il est possible de former de l'ozone à partir d'une pointe recouverte d'oxygène atomique en présence d'oxygène moléculaire gazeux. Les calculs par DFT nous laissent à penser que la formation du cation O3+ ne se fait pas à la surface mais à proximité. Ils montrent entre autres que le champ électrique déstabilise l'oxygène atomique, ce qui pourrait le pousser vers des régions où l'effet du champ est le moins intense (la tige de la pointe).

<p>During operation of heavy ion accelerators a significant pressure rise has been observed when the intensity of the high energy beam was increased. The cause for this pressure rise is ion induced desorption, which is the result when beam ions collide with residual gas molecules in the accelerator, whereby they undergo charge exchange. Since the change in charge state will affect the bending radius of the particles after they have passed a bending magnet, they will not follow the required trajectory but instead collide with the vacuum chamber wall and gas are released. For the Future GSI project FAIR (Facility for Antiproton and Ion Research) there is a need to upgrade the SIS18 synchrotron in order to meet the requirements of the increased intensity. The aim of this work was to measure the desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, Etched Cu, gold coated Cu, Ta and TiZrV coated stainless steel with argon and uranium beams at the energies 5-100 MeV/u. The measurements were performed at GSI and at The Svedberg Laboratory where a new dedicated teststand was built. It was found that the desorption yield scales with the electronic energy loss to the second power, decreasing for increasing impact energy above the Bragg Maximum. A feasibility study on the possibility to use laser refractometry to improve the accuracy of a specific throughput system was performed. The result was an improvement by up to 3 orders of magnitude, depending on pressure range.</p>

Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.

Des études de sorption/désorption ont été effectuées pour neuf contaminants émergents sélectionnés (caféine, sulfaméthoxazole, déséthylatrazine, carbamazépine, atrazine, estradiol, éthinylestradiol, noréthindrone et diclofénac) dans les boues usées provenant de trois systèmes différents. Les contaminants incluent une variété de classes de composés (pesticides, hormones et pharmaceutiques) qui possèdent des propriétés physicochimiques différentes. L’objectif de ces travaux est de modéliser leur comportement dans une station d’épuration, en présence d’une phase particulaire et d’une phase aqueuse, et du même coup, de mieux comprendre leur devenir lors de leur rejet dans l’environnement. Le coefficient octanol-eau (log Kow) permet de bien interpréter les résultats et nous permet de classer les composés selon deux types de comportements observés : les composés avec un log Kow inférieur à 3 montrent peu ou pas de sorption alors que les composés avec un log Kow supérieur à 3 montrent une sorption variant de 30 à 90 % durant les premières minutes, suivi d’une sorption lente durant les heures suivantes. Une augmentation du contenu organique favorise la sorption des composés hydrophobes alors qu’un changement de pH peut modifier la charge à la surface des particules et également la charge des analytes. Les résultats ont montré que seul le diclofénac était sensible aux variations de pH étudiés. Dans une telle situation, il est nécessaire d’utiliser le facteur d’hydrophobicité corrigé en fonction du pH (log Dow). Le coefficient de distribution solide-eau (log Kd) a été déterminé pour chaque composé à la fin de chaque expérience de sorption et se situe entre -0.3 et 2.6. Avec l’augmentation de l’hydrophobicité, la désorption diminue avec le temps et avec l’étape de rinçage. Pour simuler le relargage dans les systèmes aquatiques, les facteurs de rinçage ont été déterminés pour estimer le nombre de rinçages qui seraient nécessaire pour désorber 50 et 99 % de la concentration initialement sorbée. Les bilans de masse ont été effectués après chaque expérience dans le but de ne pas surestimer les capacités de sorption d’un composé et se situent entre 7 et 25 % pour l’estradiol, la noréthindrone et le sulfaméthoxazole et entre 44 et 103 % pour l’éthinylestradiol, l’atrazine, la déséthylatrazine, la carbamazépine, la caféine et le diclofénac. / Sorption/desorption studies were performed for nine selected emerging contaminants (caffeine, sulfamethoxazole, desethylatrazine, carbamazepine, atrazine, estradiol, ethinylestradiol, norethindrone and diclofenac) in sewage sludge from three different systems. Contaminants include a variety of compound classes (pesticides, hormones and pharmaceuticals) with different physicochemical properties. The objective of this work is to model their behavior in a treatment plant in the presence of a particulate phase and an aqueous phase, and at the same time, understanding their fate upon their release into the environment. The octanol-water partition coefficient (log Kow) allowed a good understanding of the results and allowed us to classify the compounds according to the two types of behavior observed: compounds with log Kow below 3 showed little or no sorption while compounds with log Kow over 3 showed a 30 to 90% sorption within the first few minutes, followed by a slow sorption during the next hours. An increase of the organic content promotes the sorption of hydrophobic compounds while a change in the pH can modify the charge on the surface of the particles and also the charge of the analytes. Only diclofenac was found to be sensitive to the different pH studied. In such a situation, it is necessary to use the pH-corrected hydrophobicity factor (log Dow). The solid-water distribution coefficient (log Kd) were determined for each compound at the end of each sorption experiment and ranged from 0.2 to 2.9. With increasing compounds hydrophobicity, desorption decreased with time and rinsing step. To simulate releases into aquatic systems, rinsing factors were determined to estimate the number of rinsing that would be needed to desorb 50 and 100 % of the sorbed concentration. Mass balances were performed after each experiment in order to not overestimate the sorption capacity of the compound and ranged from 7 to 25 % for estradiol, norethindrone and sulfamethoxazole and from 44 to 103 % for ethinylestradiol, atrazine, desethylatrazine, carbamazepine, caffeine and diclofenac.

Le milieu interstellaire (MIS) est la matière presente dans l'espace au sein des galaxies.Cette matière est composée de gaz et de grains de poussière. Jusqu'à présent, les radioastronomes principalement ont identifié plus de 170 molécules différentes dans le MIS.La présence de la plupart de ces molécules est expliquée à travers des réactions dans la phase gazeuse, mais la synthèse de beaucoup de ces molécules (comme H2, H2O, CO2) nécessite l'intervention d'uncatalyseur, donc des réactions dans la phase solide, sur la surface des grains de poussière. Les objectifs de cette thèse sont de comprendre quels sont les processus physico-chimiques qui ont lieu (par exemple, la diffusion et désorption) sur la surface des grains de poussière interstellaire et comment ils conduisent à la synthèse de molécules de plus en plus complexes.En particulier, l'objet de ma thèse est d'étudier:- le rôle de la diffusion des atomes d'oxygène (noté « O ») et les processus d'oxydation dans la formation des glaces interstellaires;- le couplage thermique et non thermique entre la phase gaz et la phase solide.L'astrochimie ne tendait à considérer que la diffusion des atomes d'hydrogène et les réactions d'hydrogénation, ignorant souvent le rôle de l'oxygénation ainsi que l'importance des processus d'adsorption et de désorption, d'où mes recherches approfondies sur ces thématiques.Évidemment, une meilleure connaissance de ces processus physico-chimiques et des réactions de surface aiderait les astronomes à comprendre la formation des glaces interstellaires, l'augmentation de la complexité moléculaire, et l'équilibre entre le gaz et la phase solide.Pour répondre à ces questions, de nombreuses expériences ont été réalisées avec le dispositif FORMOLISM, situé à l'Université de Cergy-Pontoise dans le cadre du LERMA (Observatoire de Paris). Via deux jets de particules avec un pompage différentiel, les atomes et les molécules sont déposés sur un échantillon froid (> 6,5 K) dans une chambre ultravide. Les produits des réactions sont ensuite sondés en utilisant la spectroscopie de masse et la spectroscopie infrarouge.Pour simuler différents environnements astrophysiques, la physique-chimie de l'état solide a été étudiée dans différentes conditions expérimentales:- La morphologie de substrat (glace d'eau amorphe soit poreuse, soit compacte, glace d'eau cristalline, silicate amorphe ou graphite)- Les espèces déposées et leur rapport relatif- La couverture des espèces déposées, de 0,1 à 2 monocouches- La température du substrat, de 6,5 à 60 K.En ce qui concerne les processus d'oxydation, les résultats montrent que l'O est très réactif avec de nombreuses espèces ; la diffusion des atomes d'O semble être beaucoup plus rapide que prévu et peut se produire par effet tunnel à des températures aussi basses que 6,5 K. Nous avons comparé les valeurs expérimentales des coefficients de diffusion et constaté que les taux de diffusion sur chaque surface, basés sur les résultats de la modélisation, étaient considérablement plus élevés que ceux prévus pour les atomes lourds tels que l'O. Nos résultats montrent que les atomes O peuvent rencontrer tous les partenaires disponibles de réaction à un taux plus rapide que le taux d'accrétion. En particulier, dans les nuages interstellaires très denses, le rapport O/H est tel que O devient l'un des partenaires réactifs dominants avec H. Ceci a un impact sur la formation de certaines espèces et sur l'abondance relative des produits formés.En ce qui concerne les processus de couplage solide-gaz (c'est à dire, l'adsorption, désorption thermique, désorption chimique), les résultats montrent que chaque processus est influencé d'une manière différente par le substrat (glace d'eau, de silicate ou graphite). Enfin, nous fournissons une liste utile des énergies de liaison de plusieurs espèces et de l'efficacité de désorption chimique des différentes réactions sur ces substrats. / The interstellar medium is the matter that exists in the space between the star systems in a galaxy. It is composed of gas and elongated tiny dust grains. To date, plenty of molecules (> 170) are known to exist in the interstellar medium. The presence of most of them can be understood in terms of gas phase reactions but the synthesis of some key species (H2, H2O, CO2) need the intervention of solid-state reactions on dust grains surface. The aims of this thesis are to understand what are the relevant physical-chemical processes (i.e., diffusion and desorption) occurring on the surface of interstellar dust grains and how these processes influence synthesis of more and more complex molecules. In particular, the focus of my thesis is the investigation of:1) the role of O-atom diffusion and the oxidation processes in the formation of interstellar ices;2) the thermal and non-thermal processes coupling gas and solid phase.The reasons of these investigations lie on the realization that, up to now, only hydrogen diffusion and hydrogenation reactions are commonly considered in solid astrochemistry and the role of oxygenation as well as the importance of adsorption and desorption processes are often disregarded.Evidently, a better knowledge of such physical-chemical processes and, in general, of the solid state physical-chemistry could help astronomers to understand the formation of interstellar ices, the increase on molecular complexity, and the equilibrium between gas and solid phase.To answer these questions, many experiments have been performed with the FORMOLISM set-up, i.e., FORmation of MOLecules in the ISM, located in the Universitè de Cergy Pontoise, Observatoire de Paris. Via two triply differentially pumped beams, atoms and molecules were aimed at a cold (>6.5 K) sample held in a Ultra high vacuum chamber. The products were probed using Mass spectroscopy and Reflexion Absorption Infrared Spectroscopy.To simulate different astrophysical environments, the solid state physical-chemistry has been studied in different experimental conditions:-The substrate morphology (Amorphous water ice, porous (p) and compact (np), crystalline (c) ice, amorphous silicate, and graphite)-The species deposited and their relative ratio-The coverage of deposited species, from 0.1 to 2 ML-The substrate temperature, from 6.5 to 60 KConcerning oxidation processes and O-atom reactivity, the results show that oxygen is very reactive with many species (i.e., H, CO, NO, H2CO, HCOOH); O diffusion appears to be much faster than previously expected and can occur via quantum mechanical tunnelling at temperatures as low as 6.5 K. We compared the experimental values of the diffusion coefficients and found that the rates of diffusion on each surface, based on modelling results, were considerably higher than those expected for heavy atoms such as oxygen. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O, OH, CO) at a faster rate than that of accretion. In particular, in very dense interstellar clouds, the O/H ratio is such that O becomes one of the dominant reactive partners together with H. This has an impact on the chemistry occurring at the surface of dust grains as either the formation of some species may be enhanced, or at least the relative abundances of the final products will be affected. An important example of how O-atom mobility can modulate the abundances of key species of ices in the ISM is the case of the H2O/CO2 ratio via the CO+O and H2CO+O pathways.Concerning gas-solid coupling processes (i.e., adsorption, sticking, thermal desorption, chemical desorption), the results show that each processes is influenced in a different way by the substrate (i.e., water ice, silicate or graphite). Moreover, we provide a useful list of binding energies of several species and chemical desorption efficiency for different reactions on different subst