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Through solving the time-dependent Schrodinger equation for the nuclear motion, quantum dynamical simulations of the water/TiO2-rutile (110) system were performed. Five-dimensional potential energy surfaces (PES) for the electronic ground and an excited state previously calculated on CASSCF (Complete Active Space Self-Consistent Field) level of theory served as the starting point for our investigations [J. Mitschker, T. Kluner, Phys. Chem. Chem. Phys. 17 (2015) 268–275]. Through investigating the motion of the water molecule by a selected series of three- and four-dimensional simulations, a precise picture of the photodissociation mechanism is obtained. Furthermore, calculations of photodissociation probabilities reveal the most favoured pathway for a complete dissociation of the adsorbate including the excitation and relaxation process as well as temperature effects.

The adsorption of NO on the rutile (TiO 2 (110)) surface has been investigated by restricted open shell Hartree–Fock (ROHF) and Moller–Plesset second order perturbation (ROMP2) theory. To mimic the TiO 2 (110) surface, a Ti 9 O 18 Mg 7 14+ -cluster embedded in a field of point charges has been employed. The preferred orientation of NO on TiO 2 (110) has been discussed in terms of 2D potential energy surfaces (PES) and a molecular orbital perspective. Adsorption energies of NO molecules in different electronic states were calculated by varying the distance coordinate and the polar angle. Our results reveal that a tilted orientation of the NO molecule on the TiO 2 (110) surface is energetically preferred.

We report on first ab initio results concerning the photodesorption of CO from a single C 60 fullerene. The weak interaction makes the use of computationally demanding electron correlation methods mandatory and we present various approaches for reducing the computational effort. The calculated adsorption energy amounts to −8.5 kJ mol −1 for the electronic ground state. The photodesorption is assumed to result from a 5 σ → 2 π ☆ excitation in the adsorbate. The interaction in the excited state is stronger and leads to an Antoniewicz-like desorption mechanism. We treated the desorption process quantum dynamically and calculated desorption probabilities and velocity distributions of the desorbing molecules.

First results concerning laser-induced photodesorption of CO molecules from a TiO 2 (1 1 0) surface are presented. For the laser-driven process an internal 5 σ → 2 π ∗ -excitation within the CO molecule is assumed. In the ground state, electrostatic forces dominate the interaction between the adsorbate and the surface. In contrast, in the excited state, the CO molecule rotates by 180° forming a covalent bond with the oxygen atom pointing downwards to the surface. Subsequent quantum dynamical simulations based on two-dimensional ab initio potential energy surfaces revealed a novel desorption mechanism, which is traced back to unusual interplay of electronic ground and excited state, respectively.

Photodesorption of small molecules from surfaces is one of the most fundamental processes in surface photochemistry. Despite its apparent simplicity, a microscopic understanding beyond a qualitative picture still poses a true challenge for theory. While the dynamics of nuclear motion can be treated on various levels of sophistication, all approaches suffer from the lack of sufficiently accurate potential energy surfaces, in particular for electronically excited states involved in the desorption scenario. In the last decade, a systematic and accurate methodology has been developed which allows a reliable calculation of accurate ground and excited state potential energy surfaces (PES) for different adsorbate–substrate systems. These potential energy surfaces serve as a prerequisite for subsequent quantum dynamical wave packet calculations, which allow for a direct simulation of experimentally observable quantities such as quantum state resolved velocity distributions. In the first part of this review, we will focus on scalar properties of desorbing diatomic molecules from insulating surfaces, where we also present a recently developed strategy of obtaining accurate potential energy surfaces using quantum chemical approaches. In general, diatomic molecules on large band gap materials such as oxide surfaces are studied which allows the use of sufficiently large cluster models and accurate ab initio methods beyond density functional theory (DFT). In the second part, we will focus on the vectorial aspects of the dynamics of nuclear motion and present simulations of experimentally accessible observables such as velocity distributions, Doppler profiles and alignment parameters. For each system, the microscopic mechanism of photodesorption is elucidated. We will demonstrate that the driving force of surface photochemistry is strongly dependent on details of the electronic structure of the adsorbate–substrate systems. This implies that great caution is advisable if experimental results are interpreted using empirical or semi-empirical models.

We established a chemical modification strategy to search for a substitute of platinum toward O2 activation. Achieving this required an understanding of the chemical bonding interactions along the corresponding reaction pathway. Using recently developed chemical bonding analysis schemes, we found that the transition state of O2 dissociation on Pt(111) is stabilized by electrostatic interactions and the bonding interaction between the two oxygen atoms. This paves the way for tuning the O2 activation barrier by replacing a surface atom with a less electronegative transition metal atom. We considered substituted Pd(111), Ag(111), and Au(111) surfaces and suggest some potential candidates for further screening by experimentalists.

The influence of the duration of the stimulating laser pulse in the photodesorption of NO from a NiO(1 0 0)-surface is studied theoretically within a two-dimensional quantum wave packet approach. The complete event including laser-induced excitation and subsequent electronic relaxation is treated consistently from first principles within the surrogate Hamiltonian approach for open quantum systems. We demonstrate that the common assumption of time-scale separation of excitation and relaxation does not hold if ultrashort femtosecond laser pulses are used. We predict a significant effect on rotational distributions of desorbing molecules if the time scales of electronic excitation and relaxation are similar.

Laser-induced desorption of NO molecules from a NiO(1 0 0) surface is studied on an ab initio level. Based on ab initio NiO-cluster calculations a three-dimensional potential energy surface was constructed for the electronic ground and a representative excited state. Quantum wave packet calculations on these surfaces allow the simulation of experimental velocity distributions of the desorbed NO molecules. Analysis of the wave packet dynamics demonstrates that the experimentally observed bimodality of the velocity distributions is caused by a bifurcation of the wave packet on the excited state potential, where the molecular motion parallel to the surface plays a decisive role.

We have studied adsorption of CO on Pd deposited on a thin FeO(1 1 1) film grown on a Pt(1 1 1) substrate using temperature programmed desorption, infrared reflection absorption spectroscopy and molecular beam techniques. At sub-monolayer Pd coverage, where formation of Pd(1 1 1) single layer islands upon heating is suggested on the basis of scanning tunneling microscopy studies, the CO desorption temperature is 70–100 K lower than on a Pd(1 1 1) single crystal, which agrees well with the results of ab initio calculations. However, annealing to 600 K results in strong reduction of the CO adsorption capacity, which is rationalized in terms of significant Pd migration through the film as revealed by angular resolved photoelectron spectroscopy measurements using synchrotron radiation. The results demonstrate the complexity of Pd interaction with the thin FeO(1 1 1) film at elevated temperatures.

The lineshape and intensity of SFG signals of CO adsorbed on supported Pd nanoparticles and Pd(1 1 1) are analyzed. For CO/Pd(1 1 1) nearly symmetric lorentzian lineshapes were observed. Applying two different visible wavelengths for excitation, asymmetric lineshapes observed for the CO/Pd/Al2O3/NiAl(1 1 0) system are explained by a lower resonant and a higher non-resonant SFG signal and a change in the phase between resonant and non-resonant signals, most likely originating from an interband transition in the NiAl substrate. The relative intensity of different CO species (hollow, bridge, on-top) was modeled by DFT calculations of IR transition moments and Raman activities. While the (experimental) sensitivity of SFG towards different CO species strongly varies, the calculated IR and Raman activities are rather similar. The inability to exactly reproduce experimental SFG intensities suggests a strong coverage dependence of Raman activities or that non-linear effects occur that can currently not be properly accounted for. � 2005 Elsevier B.V. All rights reserved.

The Hamiltonian action upon a wavefunction is the basic operation in iterative propagation schemes. Aiming at high-dimensional quantum dynamics, we introduce a parallel algorithm for a Hamiltonian action utilizing pseudospectral schemes on multidimensional grids. This algorithm is exemplified for a six-dimensional (6D) quantum dynamical system described in Fourier coordinates. The performance outcome of our parallel implementation is revealed by an almost linear overall scaled speedup that is only limited by present hardware resources. Our parallelization strategy is realized in ab initio four-dimensional (4D) quantum dynamical studies investigating the lateral dynamics of CO photodesorbing from a Cr2O3(0 0 0 1) surface. 2004 Elsevier B.V. All rights reserved.

Infrared (IR) intensities as determined by a combination of temperature dependent IR spectroscopy and temperature programmed desorption (TPD) were used to identify adsorption sites on Co and Co–Pd nano particles. It is shown that CO adsorption to metal atoms with a low metal coordination exhibits a strong intensity enhancement of the IR absorption as compared to regular surface sites. Density functional theory (DFT) calculations show that this intensity enhancement is due to a decoupling of the low coordinated metal atom bound to CO from those metal atoms embedded in the metal surface.

The influence of rovibrational preexcitation in the CO/Cr2O3(0 0 0 1)-system is studied theoretically using a three-dimensional quantum wave packet approach. We find that selectively excited hindered rotational levels of the adsorbate-substrate system influence the experimentally observed rotational alignment of the desorbing CO-molecule significantly. Pure vibrational preexcitation has less effect on the observables of interest. We predict only low surface temperature dependence of the rotational alignment and of the desorption yield. Our study is based on ab initio potential energy surfaces (PESs) for the electronic states involved and on a stochastic wave packet method.

We present a massively parallel implementation to perform quantum dynamical wave packet calculations of molecules on surfaces. The employed algorithm propagates the wavefunction via the time-dependent Schrodinger equation within a finite basis representation by Split and Chebyshev schemes, respectively. For the parallelization, a problem adapted data decomposition in all dimensions is introduced that ensures an optimal load balancing. In a speedup analysis of the timing and scaling properties, the overall semi-linear scaling of the algorithm is verified. The almost linear speedup up to 512 processing elements indicates our implementation as a powerful tool for high-dimensional calculations. The implementation is applied to laser induced desorption of molecules from surfaces.

A diabatic treatment of laser-induced desorption of small molecules from surfaces is considered to be an essential step of the theoretical quantum mechanical simulation of a DIET process on an ab initio basis. The consequences of this treatment are investigated especially with respect to the resulting velocity distributions of the desorbing species. The distributions of NO desorbing from nickel oxide surfaces are characterised by a bimodal structure. In our calculations the diabatic coupling between several investigated two-state systems is introduced via the off-diagonal elements of the Hamiltonian, which determines the time evolution of the quantum system. This procedure is the basis for a discussion of the experimentally observed features in the velocity distributions in terms of a coherent diabatic picture.

We report on ab initio and wave packet calculations with the intention of simulating the vibrational excitation of NO desorbing from a NiO(100) surface after laser irradiation. The influence of the electrostatic field above the singly positively charged surface on the N–O equilibrium distance of the NO − -like intermediate is investigated by Hartree–Fock calculations. It is shown that the field leads to a considerable shortening of the equilibrium bond length of NO − , whereas the equilibrium distance of the neutral NO molecule is only slightly modified. Taking this field effect into account, we are able to obtain quantitative agreement between experimental and theoretical vibrational state populations.

In a one-dimensional wavepacket study the role of thermal population of molecular vibrations within surface photochemistry is studied using a model potential adopted to the system NO/Cr 2 O 3 (0001). Simulations are made concerning the temperature dependence of the efficiency for UV-laser induced desorption and of velocity distributions. The course of these observables as a function of temperature is strongly dependent on the lifetime of the excited state. The results are compared with experimental results on the temperature dependence of the non-thermal desorption of NO from the Cr 2 O 3 (0001) surface after excitation at 6.4 eV. The experimentally observed increase of desorption cross-sections by about a factor of 2 when changing the surface temperature between 100 and 300 K is simulated when assuming an average resonance lifetime on the order of 10 fs. The experimentally found increase of translational energy with increasing surface temperature by ∼100 m/s is also consistent with theoretical results.

Electron spin resonance and temperature-programmed desorption spectra of thin layers of DTBN (di- tert -butyl nitroxide) adsorbed on Au(111) and NiO(111)/Au(111) surfaces have been measured. The temperature-programmed desorption data show a weak chemisorption of the DTBN molecules in the monolayer on both surfaces. On Au(111) as well as on NiO(111)/Au(111), the ESR signal from monolayer coverages is totally suppressed. This suppression continues into the multilayer regime on both substrates. Disturbances of the substrate/adsorbate interface have a strong influence on the range of the signal suppression. Possible reasons for this behavior are discussed.

In order to interpret experimental results such as velocity flux distributions and rotational/vibrational populations of the state resolved UV-laser induced desorption of NO from NiO(100) ab initio calculations at the configuration interaction (CI) and complete active space self consistent field (CASSCF) levels have been performed for the electronic ground state and those excited states which are important for the desorption process. The NO NiO(100) system was described by a NiO8−5-cluster embedded in a Madelung field of point charges with NO adsorbed in the on-top position on the central Ni2+ ion. Two-dimensional potential energy surfaces for several electronic states have been calculated as a function of the NNi distance and the tilt angle of NO towards the surface normal. The excited states involved in the desorption process are charge transfer states in which one electron is transferred from the oxygen 2p-shell into the NO 2π-orbitals. The dependence of the potential energy surfaces on the NNi distance is dominated by a strong Coulomb attraction between the NO− ion formed as an intermediate and the hole created within the cluster. The angular dependence of the potentials favours an upright adsorption geometry if NO− is approaching the surface. This offers an explanation of the strong coupling between translation and rotation, which has been observed experimentally for the system NO NiO(100) , as well as the absence of such a coupling in the system NO NiO(111) .