J. Kłos

Ab initio potential energy surface for the Ar(1S)+OH(X2Π) interaction and bound rovibrational states

Adiabatic potential energy surfaces for the 2A′ and 2A″ states of the Ar(1S)–OH(X2Π) complex were calculated using supermolecular unrestricted fourth-order Moller–Plesset perturbation theory and a large correlation consistent basis set supplemented with bond functions. The potential energy surface (PES) of the A′ state has two minima. The global minimum from the unrestricted coupled-cluster calculations with single, double, and noniterative triple excitations occurs for the collinear geometry Ar–H–O at R=7.08a0 with a well depth of De=141.2 cm−1. There is also a local minimum for the skewed T-shaped form, whereas the Ar–O–H arrangement corresponds to a saddle point. The PES of the A″ state also has two minima, which occur for the two collinear isomers. A variational calculation of the bound rovibrational states was performed. The calculated binding energy, D0=93.8 cm−1, and the energies of the bound vibrational states are in good agreement with experiment [see Berry et al., Chem. Phys. Lett. 178, 301 (199...

Ab initio potential energy and dipole moment surfaces, infrared spectra, and vibrational predissociation dynamics of the 35Cl−⋯H2/D2 complexes

Three-dimensional potential energy and dipole moment surfaces of the Cl−–H2 system are calculated ab initio by means of a coupled cluster method with single and double excitations and noniterative correction to triple excitations with augmented correlation consistent quadruple-zeta basis set supplemented with bond functions, and represented in analytical forms. Variational calculations of the energy levels up to the total angular momentum J=25 provide accurate estimations of the measured rotational spectroscopic constants of the ground van der Waals levels n=0 of the Cl−⋯H2/D2 complexes although they underestimate the red shifts of the mid-infrared spectra with v=0→v=1 vibrational excitation of the monomer. They also attest to the accuracy of effective radial interaction potentials extracted previously from experimental data using the rotational RKR procedure. Vibrational predissociation of the Cl−⋯H2/D2(v=1) complexes is shown to follow near-resonant vibrational-to-rotational energy transfer mechanism so...

Ab initio potentials for the S(3Pj)-rare gas dimers: Implementation for elastic and inelastic collisions and comparison with scattering potentials

The interaction potentials between the ground state S(3P) atom and rare gas atoms Rg (He, Ne, Ar, Kr, and Xe) in 3Π and 3Σ− states are calculated ab initio using an unrestricted CCSD(T) level of theory and extended correlation consistent basis sets augmented by bond functions. For NeS, the effects of extending the basis set, of a more accurate treatment of triple excitations within the coupled cluster method, and of the frozen core approximation are analyzed. The spin–orbit interaction is taken into account by the commonly used atomic model, whose validity is verified by the direct ab initio calculations of spin–orbit coupling matrix elements. The ab initio potentials are tested in the calculations of the absolute total scattering cross sections measured in molecular beams and compared with the potentials derived from the same data. This comparison, along with an analysis in terms of correlation formulas, proves the high accuracy of ab initio potentials and characterizes the sensitivity of scattering cros...

Nonadditive interactions in ns2 and spin-polarized ns metal atom trimers

The origins of nonadditivity in the following groups of metal trimers are examined: alkali earth metals of the IIA group (Be, Mg, and Ca), Zn as a transition metal analog of this group, spin-polarized alkali metals from IA group (Li, Na, K), and the spin-polarized Cu as its transition metal analog. The nonadditive interactions in these trimers are analyzed using the following hierarchy of approximations: the Heitler-London, self-consistent field (SCF), and correlated levels of theory. The exchange nonadditivity, which is included at the Heitler-London level, constitutes a bulk of nonadditive interactions in these systems in their equilibrium structures. The SCF treatment reveals some unphysical characteristics. At the post-SCF levels of theory the multireference character of the wave function increases from atom to dimer to trimer. The role of configurations involving excitations ns-np increases in this sequence and it is the genuine nonadditive effect. There is also a dramatic change in the characteristics of the excited states upon formation of clusters. We use the parameters of these excited states to predict which complexes are bound by the unusually strong nonadditive interactions and which are not.

Dynamics of O(3Pj)+Rg collisions on ab initio and scattering potentials

Interaction potentials of the 3Π and 3Σ− electronic states of the Rg–O(3P) systems (Rg=He–Kr) are computed at the coupled cluster single, double (triple) level of ab initio theory using extended basis sets augmented by bond functions. The ab initio potentials agree well with the scattering potentials determined from experiments in molecular beams [Aquilanti et al., J. Chem. Phys. 89, 6157 (1988)]. Both sets of the interaction potentials are employed for accurate close-coupling calculations of cross sections and rate constants for intramultiplet transitions in collisions of O(3Pj) with Rg atoms and analytical approximations for temperature dependencies of rate constants over temperature interval 50–3500 K are proposed. The sensitivity of the dynamical results to the nature of Rg atoms and interaction potentials is analyzed and the dynamics of intramultiplet mixing in O(3Pj) is investigated in both high- and low-energy limits.

Potential energy surface and rovibrational calculations for the Mg +–H2 and Mg +–D2 complexes

A three-dimensional potential energy surface is developed to describe the structure and dynamical behavior of the Mg(+)-H(2) and Mg(+)-D(2) complexes. Ab initio points calculated using the RCCSD(T) method and aug-cc-pVQZ basis set (augmented by bond functions) are fitted using a reproducing kernel Hilbert space method [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] to generate an analytical representation of the potential energy surface. The calculations confirm that Mg(+)-H(2) and Mg(+)-D(2) essentially consist of a Mg(+) atomic cation attached, respectively, to a moderately perturbed H(2) or D(2) molecule in a T-shaped configuration with an intermolecular separation of 2.62 Å and a well depth of D(e) = 842  cm(-1). The barrier for internal rotation through the linear configuration is 689  cm(-1). Interaction with the Mg(+) ion is predicted to increase the H(2) molecules bond-length by 0.008 Å. Variational rovibrational energy level calculations using the new potential energy surface predict a dissociation energy of 614  cm(-1) for Mg(+)-H(2) and 716  cm(-1) for Mg(+)-D(2). The H-H and D-D stretch band centers are predicted to occur at 4059.4 and 2929.2  cm(-1), respectively, overestimating measured values by 3.9 and 2.6  cm(-1). For Mg(+)-H(2) and Mg(+)-D(2), the experimental B and C rotational constants exceed the calculated values by ∼1.3%, suggesting that the calculated potential energy surface slightly overestimates the intermolecular separation. An ab initio dipole moment function is used to simulate the infrared spectra of both complexes.

Properties of the B+-H2 and B+-D2 complexes: a theoretical and spectroscopic study

The rotationally resolved infrared spectrum of the B(+)-D(2) ion-neutral complex is recorded in the D-D stretch vibration region (2805-2875  cm(-1)) by detecting B(+) photofragments. Analysis of the spectrum confirms a T-shaped equilibrium geometry for the B(+)-D(2) complex with a vibrationally averaged intermolecular bond length of 2.247 Å, around 0.02 Å shorter than for the previously characterised B(+)-H(2) complex [V. Dryza, B. L. J. Poad, and E. J. Bieske, J. Am. Chem. Soc. 130, 12986 (2008)]. The D-D stretch band centre occurs at 2839.76 ± 0.10 cm(-1), representing a -153.8  cm(-1) shift from the Q(1)(0) transition of the free D(2) molecule. A new three dimensional ab initio potential energy surface for the B(+)+H(2) interaction is calculated using the coupled cluster RCCSD(T) method and is used in variational calculations for the rovibrational energies of B(+)-H(2) and B(+)-D(2). The calculations predict dissociation energies of 1254  cm(-1) for B(+)-H(2) with respect to the B(+)+H(2) (j = 0) limit, and 1313  cm(-1) for B(+)-D(2) with respect to the B(+)+D(2) (j = 0) limit. The theoretical approach reproduces the rotational and centrifugal constants of the B(+)-H(2) and B(+)-D(2) complexes to within 3%, and the magnitude of the contraction of the intermolecular bond accompanying excitation of the H(2) or D(2) sub-unit, but underestimates the H-H and D-D vibrational band shifts by 7%-8%. Combining the theoretical and experimental results allows a new, more accurate estimation for the B(+)-H(2) band origin (3939.64 ± 0.10  cm(-1)).