Singlet-triplet excitation spectrum of the CO-He complex. II. Photodissociation and bound-free CO(a (3)Pi <- X-1 Sigma(+)) transitions

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Diabatic intermolecular potentials and bound states of open-shell atom-molecule dimers: Application to the F(P-2)-H-2 complex

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Singlet-triplet excitation spectrum of the CO-He complex. I. Potential surfaces and bound-bound CO(a (3)Pi <- X-1 Sigma(+)) transitions

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A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

First-principles extrapolation method for accurate CO adsorption energies on metal surfaces

We show that a simple first-principles correction based on the difference between the singlet-triplet CO excitation energy values obtained by DFT and high-level quantum chemistry methods yields accurate CO adsorption properties on a variety of metal surfaces. We demonstrate a linear relationship between the CO adsorption energy and the CO singlet-triplet splitting, similar to the linear dependence of CO adsorption energy on the energy of the CO 2$\pi$* orbital found recently {[Kresse {\em et al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations underestimate the CO singlet-triplet excitation energy $\Delta E_{\rm S-T}$, whereas coupled-cluster and CI calculations reproduce the experimental $\Delta E_{\rm S-T}$. The dependence of $E_{\rm chem}$ on $\Delta E_{\rm S-T}$ is used to extrapolate $E_{\rm chem}$ for the top, bridge and hollow sites for the (100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to the coupled-cluster and CI $\Delta E_{\rm S-T}$ value. The correction reproduces experimental adsorption site preference for all cases and obtains $E_{\rm chem}$ in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure

Entrance Channel X-HF (X=Cl, Br, and I) Complexes studied by High-Resolution Infrared Laser Spectroscopy in Helium Nanodroplets

Rotationally resolved infrared spectra are reported for halogen atom - HF free radical complexes formed in helium nanodroplets. An effusive pyrolysis source is used to dope helium droplets with Cl, Br and I atoms, formed by thermal dissociation of Cl$_2$, Br$_2$ and I$_2$. A single hydrogen fluoride molecule is then added to the droplets, resulting in the formation of the X-HF complexes of interest. Analysis of the resulting spectra confirms that the observed species have $^2\Pi_{3/2}$ ground electronic states, consistent with the linear hydrogen bound structures predicted from theory. Stark spectra are also reported for these species, from which the permanent electric dipole moments are determined.Comment: 41 pages, 16 figures, 5 table

Dynamics of open-shell van der Waals complexes

Contains fulltext : 60679.pdf (publisher's version ) (Open Access)This thesis deals with open-shell atom-diatom complexes which are of interest because they can be considered as model systems for complexes of larger open-shell molecules. Intermolecular potential surfaces were computed by means of ab initio electronic structure calculations or taken from the literature. The bound levels of the complex were obtained by solving the Schrödinger equation for the nuclear motion problem. The standard harmonic oscillator approach to solve this problem is not applicable here, because of the large amplitude internal motions in these weakly bound complexes. Instead, the bound levels were obtained by solving a coupled-channel problem in Jacobi coordinates. Photodissociation of complexes, a half-collision, was studied with the aid of full coupled-channel scattering calculations. The two-step procedure to treat the electronic and nuclear motion problems is similar to the Born-Oppenheimer model, but it should be emphasized that the standard Born-Oppenheimer or adiabatic approximation is not valid for these open-shell complexes. The electronic states of the complex become degenerate, i.e., the corresponding adiabatic potential energy surfaces coincide, at linear geometries and for a large distance between the interacting molecules. Non-adiabatic coupling between different electronic states that originates from the nuclear kinetic energy operator becomes important in these regions. A generalized Born-Oppenheimer model was applied that involves the multiple asymptotically degenerate electronic states simultaneously and takes into account the non-adiabatic coupling between these states. This coupling was not explicitly considered, however, but the adiabatic states were transformed into diabatic states that are no longer coupled by the nuclear kinetic energy operator. This approach is briefly explained in Chapter 2 of the thesis. It was applied to several atom-diatom complexes with either the atom or the diatom being an open-shell system in Chapters 3 to 7RU Radboud Universiteit Nijmegen, 17 maart 2004Promotor : Avoird, A. van der Co-promotor : Groenenboom, G.C.161 p

Theoretical study of the He-HF+ complex. II. Rovibronic states from coupled diabatic potential energy surfaces

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Bound states of the Cl(P-2)-HCl van der waals complex from coupled ab initio potential energy surfaces

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