CO Axis Research Articles

Shape effect of Co nanoparticles on the electric and magnetic properties of Co–SiO2 nanogranular films

Controlling the magnetic anisotropy of nanoparticles is a crucial but challenging step for developing new magnetic functions. Here, we demonstrate a simple approach to controlling the shape of Co nanoparticles in a Co-SiO2 nanogranular film from oblate to prolate spheroid by varying the substrate rotation speed during the tandem fabrication process without changing the film composition (Co:SiO2 = 3:7). Changing the nanoparticles from oblate to prolate, increasing perpendicular length of ellipsoidal nanoparticles, changes the magnetic anisotropy axis of Co–SiO2 nanogranular films from in-plane to out-of-plane, which indicates that the shape anisotropy profoundly affects the magnetic properties. Despite the small tunneling current of a few tens of nanoamperes, a maximum tunneling magnetoresistance effect of up to 2.8 % was realized under an applied magnetic field of 12 kOe in the film plane. Achieving both in-plane and perpendicular spin-dependent tunneling, the anisotropic nanogranular films imply direction controllable tunneling materials as future topological nanoarchitecture. Such high-resistivity nanogranular films with a controllable magnetic nanoparticle shape facilitate the design of new magneto-optical devices with high withstand voltages.

Atomic Force Extrema Induced by the Bending of a CO-Functionalized Probe.

The control and observation of reactants forming a chemical bond at the single-molecule level is a long-standing challenge in quantum physics and chemistry. Using a single CO molecule adsorbed at the apex of an atomic force microscope tip together with a Cu(111) surface, bending of the molecular probe is induced by torques due to van der Waals attraction and Pauli repulsion. As a result, the vertical force between CO and Cu(111) exhibits a characteristic dip-hump evolution with the molecule-surface separation, which depends sensitively on the initial tilt angle the CO axis encloses with the surface normal. The experimental force data are reproduced by model calculations that consider the CO deflection in a harmonic potential and the molecular orientation in the Pauli repulsion term of the Lennard-Jones potential. The presented findings shed new light on vertical-force extrema that can occur in scanning probe experiments with functionalized tips.

The Physical Properties of S0 Galaxy PGC 26218: The Origin of Starburst and Star Formation

We present 2D-spectroscopic observations from Centro Astron\'omico Hispano Alem\'an (CAHA) 3.5 m telescope and the millimetre observation from NOrthern Extended Millimeter Array (NOEMA) of the nearby S0 galaxy PGC 26218, which shows central star-formation activity and post-starburst outside in the disk. We estimate the star formation rate (SFR = $0.28\pm0.01$ $M_{\odot} \rm yr^{-1}$) and molecular gas mass ($\rm log\ $$M_{\rm H_{2}}=7.60\pm0.15\ M_{\odot}$) of PGC 26218 based on the extinction-corrected H$\alpha$ emission line and the CO-$\rm H_{2}$ conversion factor ($\alpha_{\rm CO}$) of the Milky Way, respectively. We find that PGC 26218 follows the star forming main sequence (SFMS) and the Kennicutt-Schmidt law. Comparing the kinematics of CO($J$=1-0), stars and H$\alpha$, we find that the rotational axis of CO($J$=1-0) is 45$^{\circ}$ different from that of H$\alpha$. In addition, the profile of the CO($J$=1-0) emission line shows asymmetry and has an inflow component of $\sim$ 46 $\rm km\ s^{-1}$. With the decomposition of the optical image, we confirm that PGC 26218 shows multiple nuclear structures. The projected offset between the most luminous optical center and the center of CO($J$=1-0) is $5.2\arcsec$ ($\sim$ 0.6 kpc) and the latter overlaps with one of the optical cores. These results support that PGC 26218 may have experienced a gas-rich minor merger, extending its star formation and locating it in the SFMS.

Experimental and kinetic modelling investigation on NO, CO and NH3 emissions from NH3/CH4/air premixed flames

Ammonia (NH3) is regarded as one of the most viable alternatives to produce carbon-free energy. However, its low flammability and high NOx emissions associated with its combustion inhibit the implementation of pure NH3 as a fuel. Dual-fuel approaches with NH3 and more reactive fuels have been proposed; however, information on pollutant emissions is still scarce. The present work focuses on quantifying the gaseous pollutant emissions from the combustion of mixtures of NH3 and CH4 as a function of the equivalence ratio and amount of NH3 in the fuel mixture. A premixed laminar burner was fired with various mixtures of NH3/CH4 in air with equivalence ratios of 0.8, 0.9 and 1, and a fixed thermal input of 300 W. The NH3 molar fraction in the fuel mixture was varied from 0 (pure CH4) up to 0.7. Gas temperatures along the burner axis and emissions of NOx, CO and NH3 were measured for all conditions. The results were compared with kinetic simulations using recent chemical kinetic mechanism models. The experimental results showed that the NOx concentration initially increases as the fraction of NH3 in the fuel mixture rises up to 0.5, decreasing afterwards. Furthermore, NOx emissions decrease as the equivalence ratio is reduced towards fuel-lean conditions. CO and NH3 emissions are fairly low indicating complete combustion of CH4 and NH3. The chemical kinetic mechanisms considered showed fair agreement with the experimental trends, with the NOx and CO emissions being over-predicted for most conditions.

The HH30 edge-on T Tauri star

Context. The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming protostar. HH30 is a rare and beautiful example of a pre-main sequence star exhibiting a flared edge-on disk, an optical jet, and a CO molecular outflow, making this object a case study for the disk-jet-outflow paradigm. Aims. We aim to clarify the origin of the small-scale molecular outflow of HH30 and its link and impact on the accretion disk. Methods. We present ALMA 0.25″ angular resolution observations of the circumstellar disk and outflow around the T Tauri star HH30 in the dust continuum at 1.33 mm and of the molecular line transitions of 12CO(2–1) and 13CO(2–1). We performed a disk subtraction from the 12CO emission, from which we analysed the outflow properties in detail in the altitudes z ≲ 250 au. We fit the transverse position-velocity diagrams across the 12CO outflow to derive the ring positions and projected velocity components (including rotation). We use the results of these fits to discuss the origin of the CO outflow. Results. The 1.3 mm continuum emission shows a remarkable elongated morphology along PA = 31.2∘ ± 0.1∘ that has a constant brightness out to a radius of r = 75 au. The emission is marginally resolved in the transverse direction, implying an intrinsic vertical width ≤24 au and an inclination to the line-of-sight i ≥ 84.8∘. The 13CO emission is compatible with emission from a disk in Keplerian rotation, in agreement with the previous findings. The monopolar outflow, detected in 12CO, arises from the north-eastern face of the disk from a disk radius r ≤ 22 au and extends up to 5″ (or 700 au) above the disk plane. We derive a lower limit to the total mass of the CO cavity/outflow of 1.7 × 10−5 M⊙. The CO cavity morphology is that of a hollow cone with semi-opening angle ∼35∘. The derived kinematics are consistent with gas flowing along the conical surface with constant velocity of 9.3 ± 0.7 km s−1. We detect small rotation signatures (Vϕ sin i ∈ [0.1; 0.5] km s−1) in the same sense as the underlying circumstellar disk. From these rotation signatures we infer an average specific angular momentum of the outflow of 38 ± 15 au km s−1 at altitudes z ≤ 250 au. We also report the detection of small amplitude wiggling (1.2∘) of the CO axis around an average inclination to the line of sight of i = 91∘. Conclusions. The derived morphology and kinematics of the CO cavity are compatible with expectations from a slow disk wind, originating either through photo-evaporation or magneto-centrifugal processes. Under the steady assumption, we derive launching radii in the range 0.5–7 au. In that scenario, we confirm the large minimum mass flux of 9 × 10−8 M⊙ yr−1 for the CO wind. The wind would therefore extract a significant amount of the accreted mass flux through the disk and would likely play a crucial role in the disk evolution. If the CO flow originates from a steady-state disk wind, our ALMA observations rule out the 18 au binary orbital scenario previously proposed to account for the wiggling of the optical jet and favour instead a precession scenario in which the CO flow originates from a circumbinary disk around a close (separation ≤ 3.5 au) binary. Alternatively, the CO outflow could also trace the walls of a stationary cavity created by the propagation of multiple bow shocks. Detailed numerical simulations are under way to fully test the entrainment hypothesis.

Heme oxygenase-1/carbon monoxide axis suppresses transforming growth factor-β1-induced growth inhibition by increasing ERK1/2-mediated phosphorylation of Smad3 at Thr-179 in human hepatocellular carcinoma cell lines

Heme oxygenase-1 (HO-1) has been implicated in tumor progression, but the underlying molecular mechanisms remain largely unknown. Transforming growth factor-β1 (TGF-β1) exhibits cytostatic and apoptotic effects in hepatocytes and several types of hepatocellular carcinoma (HCC) cell lines, and deregulation of its signaling pathway is linked to hepatic tumorigenesis. In the present study, we observed that HO-1 is expressed at higher levels in HCC tissues than in paired normal tissues. Moreover, TGF-β1-induced cell cycle arrest and up-regulation of cyclin-dependent kinase inhibitors in HCC cell lines were significantly attenuated by overexpression of HO-1 or treatment with tricarbonyldichlororuthenium(II) dimer ([Ru(CO)3Cl2]2, suggesting an inhibitory role of the HO-1/CO axis in TGF-β signaling to growth inhibition in HCC cell lines. Interestingly, we observed that [Ru(CO)3Cl2]2 inhibits TGF-β1-induced Smad3-dependent reporter activity without affecting its C-terminus phosphorylation, complex formation with Smad4, and nuclear translocation. Additional experiments revealed that HO-1/CO axis selectively induces phosphorylation of Smad3 at Thr-179 residue in the linker region through activation of extracellular signal-activated kinase (ERK) 1/2. Transfection with a phospho-deficient Smad3 (T179A) mutant or treatment with FR180204, a specific inhibitor for ERK1/2, significantly reversed the inhibitory effects of HO-1 and [Ru(CO)3Cl2]2 on cell cycle arrest induced by TGF-β1. These findings for the first time demonstrate that HO-1/CO axis confer resistance of HCC cells to TGF-β growth inhibitory signal by increasing Smad3 phosphorylation at Thr-179 via ERK1/2 pathway.

Pure Even Harmonic Generation from Oriented CO in Linearly Polarized Laser Fields.

The first high harmonic spectrum containing only the odd orders was observed in experiments 30 years ago. However, a spectrum containing pure even harmonics has never been observed. We investigate the generation of pure even harmonics from oriented CO molecules in linearly polarized laser fields employing the time-dependent density-functional theory. We find that the even harmonics, with no odd orders, are generated with the polarization perpendicular to the laser polarization when the molecular axis of CO is perpendicular to the laser polarization. The generation of pure even harmonics reveals a type of dipole acceleration originating from the permanent dipole moment. This phenomenon exists in all systems with permanent dipole moments, including bulk crystal and polyatomic molecules.

Coexistence of perpendicular and in-plane exchange bias using a single ferromagnetic layer in Pt/Co/Cr/CoO thin film

We studied the temperature dependence of magnetization and exchange bias in a Pt/Co/Cr/CoO multilayer thin film. These magnetic multilayers are of particular interest since the easy axis of ultra-thin Co is strongly affected by the interfacial anisotropies of neighbouring Pt and Cr layers. The room temperature measurements show that the sample has a magnetic easy axis only in the film plane. However, upon cooling the sample, the easy axis of the magnetization departs from its initial orientation and typical easy-axis hysteresis loops are obtained for both in-plane and perpendicular directions. In accordance with this change in the magnetization direction at lower temperatures, the sample shows an unexpected coexistence of perpendicular and in-plane exchange bias below the antiferromagnetic transition of CoO. The temperature dependence of the exchange bias field for both directions is also significantly different. Along the film plane, the exchange bias field monotonically decreases and disappears at 220 K with increasing temperature. For the perpendicular direction, however, the exchange bias field increases and reaches a maximum value at 80 K. Then it decreases and disappears at 150 K with further increasing temperature. The mechanisms behind this anomalous temperature dependence of the exchange bias as well as the step-like behaviour in the hysteresis curves are discussed.

Roaming Under the Microscope: Trajectory Study of Formaldehyde Dissociation.

The photodissociation of formaldehyde was studied using quasi-classical trajectories to investigate "roaming," or events involving trajectories that proceed far from the minimum energy pathway. Statistical analysis of trajectories performed over a range of nine excitation energies from 34 500 to 41 010 cm(-1) (including zero-point energy) provides characterization of the roaming phenomenon and insight into the mechanism. The trajectories are described as projections onto three coordinates: the distance from the CO center of mass to the furthest H atom and the azimuthal and polar coordinates of that H atom with respect to the CO axis. The trajectories are used to construct a "minimum energy" potential energy surface showing the potential for any binary combination of these three coordinates that is at a minimum energy with respect to values of the other coordinates encountered during the trajectories. We also construct flux diagrams for roaming, transition-state, and radical pathways, as well as "reaction configuration" plots that show the distribution of reaction geometries for roaming and transition-state pathways. These constructs allow characterization of roaming in formaldehyde as, principally, internal rotation of the roaming H atom around the CO axis at a slowly varying and elongated distance from the CO center of mass. The rotation is nearly uniform, and is sometimes accompanied by rotation in the polar coordinate. The roaming state of formaldehyde can be treated as a separate kinetic entity, much as one might treat an isomer. Rate constants for the formation of and reaction from this roaming state are derived from the trajectory data as a function of excitation energy.

NMR Studies on Solution Structures of Methanol and Ethanol Saturated with CO2

2H and 17O NMR relaxation times, T 1(2H) and T 1(17O), and 2H NMR chemical shifts, δ(2H), in CO2-saturated CD3OD and C2D5OD solutions were measured at 313.2 K over the pressure range up to ~6 MPa. The rotational correlation times, τ r, of the CD and OD axes within CD3OD and C2D5OD molecules and the CO axis within the CO2 molecule were determined from T 1(2H) and T 1(17O), and the magnetic susceptibility-corrected chemical shifts, δ corr, were derived from δ(2H). The differences in τ r and δ corr observed between the two alcohol systems: τ r and δ corr of OD in C2D5OD, decreased rapidly with increasing CO2 concentration, while those of OD in CD3OD remained almost unchanged at mole fractions of CO2, $$ x_{\text CO_{2}} $$ , lower than ~0.25 and then slightly decreased at higher $$ x_{\text CO_{2}} $$ . The hydrogen bonding structure in C2D5OD was found to be gradually broken down by CO2 dissolution. On the other hand, in CD3OD, it has been revealed that the hydrogen bonding structure can persist at $$ x_{\text CO_{2}} $$ < ~0.25 but then collapses at higher $$ x_{\text CO_{2}} $$ .

Electrochemical nucleation behaviours and properties of electrodeposited Co–Ni alloy thin films

The electrocrystallisation of Co, Ni and Co–Ni alloys on ruthenium surface from chloride baths has been studied by cyclic voltammetry and chronoamperometry measurements. The structural and magnetic properties were studied by X-ray diffraction and alternating gradient force magnetometer techniques respectively. The Co–Ni alloys were deposited from solution with molar ratios (Co/Ni) of 5∶1, 1∶1 and 1∶5. From cyclic voltammetry measurements, for all molar ratios for electrodeposited Co–Ni, preferential deposition of Co occurs and anomalous codeposition takes place. Therefore, variation in the composition of thin films alloy is possible depending on the deposition potential. The Scharifker and Hills model was employed to analyse the current transients. For both Co and Co–Ni alloys, the nucleation was a good agreement with the instantaneous model followed by three-dimensional diffusion limited growth. However, for Ni after tmax, the nucleation process changes from progressive to instantaneous model. It is evident that the compositions of the electrolyte do not have influence on the type of nucleation for Co–Ni alloys. X-ray diffraction measurements indicate a small crystallite size with the presence of a mixture of hcp and fcc Co–Ni structures. The hysteresis loops with a magnetic field in the parallel and perpendicular directions showed that the easy magnetisation axis of Co–Ni thin film is in the film plane.

Magnetization Reversal Mechanism in FeCoNiB Nanowire Arrays

The structural and magnetic properties of Fe13Co15.5Ni51.5B20 nanowire arrays have been investigated. The easy axis would be expected to lie along the nanowire axis, due to the contribution of the shape anisotropy. However, the c axis of Co in the alloy results in an orientation perpendicular to the nanowires as it has been observed from the hysteresis loops. Changing the current values results in changes of the deposition potential, allowing a percentage increase or decrease in the deposition of Ni, Co and Fe. This leads to a change of the easy axis from the axial to transverse direction. Coercivity values obtained from the magnetic hysteresis loops allowed the study of the magnetization reversal processes. It has been shown that the reversal process occurs as a result of the nucleation of a single domain with a volume 200 times smaller than the volume of the nanowire. The switching field for the investigated nanowires is explained based on the 'curling' mode given by the model for infinite cylinders. The calculated values of the reduced coercivity h c show that 'curling' alone cannot explain the magnetization reversal. This allowed us to state that it must be a multi-domain structure with domains aligned along the transverse direction. Thus, the magnetization reversal would consist not of a single wall displacement but a series of them.

Theoretical and Experimental Study of the Rovibrational Spectrum of He2−CO

We report calculated microwave and infrared ro-vibrational transitions of the van der Waals complex He(2)-CO. The calculations were done using a product basis and a Lanczos eigensolver, together with He-CO and He-He potential functions taken from the literature. The results are found to be in good agreement with previously reported experimental results, and they enable the experimental assignments to be clarified, augmented, and (in one case) corrected. Unlike some other van der Waals complexes with two He atoms such as He(2)-N(2)O, it is not possible to associate a set of energy levels with the "torsional" motion of the two He atoms on a ring encircling the dopant (in this case CO). Although we assume that the dipole moment is along the CO axis we find nonetheless that many transitions have appreciable intensity due to ro-vibrational coupling.

Thermal decomposition of allantoin as probed by matrix isolation FTIR spectroscopy

The optimized geometries, energies of the possible conformers of allantoin (2,5-dioxo-4-imidazolidinyl urea, the diureide of glyoxylic acid) as well as the barriers for conformational interconversion have been calculated using the density functional theory [DFT(B3LYP)/6-311++G(d,p)] method. The calculations predicted the existence of four conformers ( gC, tT, g′C, and g′T; where the first and second symbols in the name of the conformers designate the conformation around the exocyclic NHC–NHCO and CNH–CO axes, respectively), with the gC form contributing to more than 98% of the population in gas phase at room temperature. This conformer is different from that corresponding to the monomeric unit found in crystalline RS-allantoin ( g′C; Mootz, D. Acta Crystallogr. 1965, 19, 726), stressing the importance of intermolecular H-bonding in determining the structure of the crystal. Upon sublimation under vacuum (10 −6 mbar), the compound was found to undergo extensive decomposition to urea, isocyanic acid, NH 3, and carbon. The identification of the decomposition products was made by using matrix isolation infrared spectroscopy. In consonance with the theoretical predictions, the allantoin molecules surviving thermal decomposition were found to undergo conformational isomerization and be present in the cryogenic argon matrix in both the gC and g′C conformations. The solid state room temperature infrared spectrum of allantoin was also investigated and assigned.

How Do Hydrogen Bonds Break in Small Alcohol Oligomers?

Recent infrared pump-probe studies on alcohol oligomers in CCl(4) solution reveal that, following OH stretch excitation, ultrafast hydrogen bond (H-bond) breaking takes place on a time scale of 1 ps. To shed light on the mechanism of the H-bond breaking, we consider vibrational predissociation of the H-bonded methanol dimer. We construct a four-dimensional model for the dimer including the H-bond stretch, the donor OH stretch, the donor COH bend, and the OH rotation about the CO axis of the donor. Predissociation rates are calculated with Fermi's golden rule and close coupling approaches. Our results indicate that the predissociation leads to products with highly excited OH rotations. The predissociation rates strongly depend on the hydrogen bond strength. From our results, a simple nonadiabatic curve crossing picture for the predissociation process emerges, which provides a framework for future studies of solvent-assisted vibrational predissociation.

Hydrogen production by thermal partial oxidation of hydrocarbon fuels in porous media based reformer

The thermal partial oxidation process of methane was investigated numerically and experimentally. Thermodynamic calculations and kinetic simulation were performed using CHEMKIN tools to determine the practical operating conditions. Experimentally, a porous material-based reactor was built to perform the partial oxidation process. Temperature profiles along the reactor central axis and concentration profiles of CO, H 2, CO 2, C 2H 2 and CH 4 were measured. Two different porous structures were installed in the reaction zone: Al 2O 3 fiber static mixer structures and SiC foams. The effects of air preheating temperature, thermal load and air ratio on the reforming process were investigated for both structures. The numerical calculation showed that an air ratio down to 0.4 is a practical limit to perform the partial oxidation process. Experimentally, it was found that the air preheating temperature has no significant influence on the syngas composition; however, it does affect the soot point ( λ c). Higher heat recuperation was detected in the case of SiC foam based reformer than in the case of the Al 2O 3 mixer one. The SiC foam based reactor showed also a better performance than the Al 2O 3 regarding the soot point. For air preheating temperature of 700 °C, the current soot point for the SiC foam based reformer was 0.42, while it was 0.45 for the Al 2O 3 mixer one.

Investigation of the enhanced solubility of fluorinated methanes in CO 2 by Monte Carlo simulation: Absolute free energy of solvation and structural properties of solution

The absolute free energy of solvation of methane (CH 4) and its fluorinated forms (CH 3F, CH 2F 2, CHF 3 and CF 4) have been computed via statistical perturbation theory (SPT) in the NPT ensemble at four thermodynamical states (whitin liquid and supercritical regions), in the context of Monte Carlo Simulations. Thermodynamical interpretation of the observed trend in the absolute free energy of solvation in different states reveals an exothermic solvation with Δ S slv < 0 (entropically unfavorable solvation) that the intermolecular interactions play an important role in the solvation process. The fluorinated methanes are confirmed to control the mutual arrangement of neighboring CO 2 molecules and the axis of CO 2 molecules near F atom of fluorinated solutes make a right angle with F(solute)–C(CO 2) axis. Moreover, the energetic distribution along with structural and orientational distributions confirm the existence of a direct interaction between CO 2 and F atom, although the extent of this interaction is not very large.

The growth of thin fluorescein films on Ag (1 1 0)

The thin fluorescein films grown on Ag (110) have been studied by the ultraviolet photoemission spectroscopy (UPS). Four emission features are located at 2.7, 3.8, 7.4 and 9.8eV below the Fermi level, respectively. The angle-resolved ultraviolet photoemission spectroscopy (ARUPS) measurements show that the Triring plane of fluorescein is nearly parallel to the substrate and the axis of CO is close to the [1 1¯ 0] azimuth.

Low-Thrust Spacecraft Formation Keeping

Replacing large and costly satellites with formations of smaller satellites, flying in close proximity, is a current subject of interest. One of the keys to successful formation flying is the control system that maintains the formation geometry and provides proper positioning of each member of the formation. This study compares two active control system designs that can be used to maintain a formation composed of microsatellites with limited on-off thrusting capabilities in low Earth orbit. The two evaluated designs are based on a linear approach using optimal control theory and on a nonlinear approach based on Lyapunov stability concepts. In assessing the effectiveness of each controller, the performance criteria were the accuracy with which the formation is maintained and the propellant consumption. The final selection is a tradeoff between fuel consumption and controller robustness based on model uncertainties. Nomenclature amrs = semimajor axis of leader orbit Co = controllability matrix e3 = unit vector fixed in the Earth along the direction of the north pole axis Fx , Fy, Fz = components of the control force along the rotating x, y, and z axes, respectively f = control force vector (force applied by the onboard propulsion system) J = cost function associated with the optimal control J2 = Earth oblateness harmonic coefficient Kglobal, = positive gains associated with the nonlinear

Activation of C–H, C–C and C–I bonds by Pd and cis-Pd(CO) 2I 2. Catalyst–substrate adaptation

We have studied the oxidative addition reactions of methane and ethane C–H, ethane C–C and iodomethane C–I bonds to Pd and cis-Pd(CO) 2I 2 at the ZORA-BP86/TZ(2)P level of relativistic density functional theory (DFT). Our purpose, besides exploring these particular model reactions, is to understand how the mechanism of bond activation changes as the catalytically active species changes from a simple, uncoordinated metal atom to a metal–ligand coordination complex. For both Pd and cis-Pd(CO) 2I 2, direct oxidative insertion (OxIn) is the lowest-barrier pathway whereas nucleophilic substitution (S N2) is highly endothermic, and therefore not competitive. Introducing the ligands, i.e., going from Pd to cis-Pd(CO) 2I 2, causes a significant increase of the activation and reaction enthalpies for oxidative insertion and takes away the intrinsic preference of Pd for C–I over C–H activation. Obviously, cis-Pd(CO) 2I 2 is a poor catalyst in terms of activity as well as selectivity for one of the three bonds studied. However, its exploration sheds light on features in the process of catalytic bond activation associated with the increased structural and mechanistic complexity that arises if one goes from a monoatomic model catalysts to a more realistic transition-metal complex. First, in the transition state (TS) for oxidative insertion, the C–X bond to be activated can have, in principle, various different orientations with respect to the square-planar cis-Pd(CO) 2I 2 complex, e.g., C–X or X–C along an I–Pd–CO axis, or in between two I–Pd–CO axes. Second, at variance to the uncoordinated metal atom, the metal complex may be deformed due to the interaction with the substrate. This leads to a process of mutual adjustment of catalyst and substrate that we designate catalyst–substrate adaptation. The latter can be monitored by the Activation Strain model in which activation energies Δ E ≠ are decomposed into the activation strain Δ E strain ≠ of and the stabilizing TS interaction Δ E int ≠ between the reactants in the activated complex: Δ E ≠ = Δ E strain ≠ + Δ E int ≠ .