Interactions and collisions of cold molecules: lithium + lithium dimer

There is at present great interest in the properties of ultracold molecules. Molecules are created in traps in excited rovibrational states and any vibrational relaxation results in the trap loss. This thesis provides a theoretical study of interactions and collisions in the spin-polarized lithium -b lithium dimer system at ultralow energies. Potential energy surface of the electronic quartet ground state of lithium trimer is generated ab initio using the CCSD(T) method and represented by an IMLS/Shepard fit. Long-range nonadditive interactions are modelled using a symmetric global form with coefficients taken from a fit to the atom-molecule dispersion coefficients. The surface allows barrierless atom-exchange reactions. It has a global minimum of ≈ 4000 cm(^-1) at equilateral geometries with r(_e) = 3.1 Å. The nonadditive interactions are very strong near equilibrium. They increase the well depth by a factor of 4 and reduce the interatomic distance by ≈ 1 Å. Another surface of À symmetry in C(_s) meets the ground state surface at linear geometries at short range. Part of the seam, near D(_ooh) geometries, is in an energetically accessible region for cold collisions. Inside the seam, the lowest À surface correlates with (^4)II rather than (^4)Σ state. Inelastic and reactive collisions are investigated using a quantum mechanical coupled channel method in hyperspherical coordinates. Bosonic and fermionic systems in the spin-stretched states are considered. The inelastic rate coefficients from the rovibrationally excited states of dimer at ultralow collision energies are large, often above 10-(^-10) cm(^3)s(^-1) The elastic cross sections are ≈ 3 orders of magnitude lower at 1 nK. Atom-molecule mixtures, at the densities found in Bose-Einstein condensates of alkali metal atoms that were recently produced, would last only a fraction of a second. Classical Langevin model describes semi-quantitatively the energy dependence of inelastic cross sections above ≈ 50 mK. No systematic differences between the bosonic and fermionic systems were found. Sensitivity of the results on potential was investigated. Reactions in isotopic mixtures of lithium may be exothermic even from the molecular ground state. The reactive rate coefficients are 1 - 2 orders of magnitude smaller than those in systems involving an initially vibrationally excited dimer

Long range intermolecular forces in triatomic systems: connecting the atom-diatom and atom-atom-atom representations

The long-range forces that act between three atoms are analysed in both atom-diatom and atom-atom-atom representations. Expressions for atom-diatom dispersion coefficients are obtained in terms of 3-body nonadditive coefficients. The anisotropy of atom-diatom C_6 dispersion coefficients arises primarily from nonadditive triple-dipole and quadruple-dipole forces, while pairwise-additive forces and nonadditive triple-dipole and dipole-dipole-quadrupole forces contribute significantly to atom-diatom C_8 coefficients. The resulting expressions are applied to dispersion coefficients for Li + Li_2 (triplet) and recommendations are made for the best way to obtain global triatomic potentials that dissociate correctly both to three separated atoms and to an atom and a diatomic molecule.Comment: To be published in a special issue of Molecular Physics in honour of Mark Chil

Ozon u graničnom sloju u Osijeku, istočna Hrvatska

Results of the first ozone monitoring in ambient air in eastern Slavonia are reported for the growth season in 2002 (April through September). The monitoring site at the northern boundary of the city was chosen to distinguish two types of air masses: one from the rural and marshy region to the north and the other urban and suburban from the south. The measured hourly average ozone volume fractions varied between 0 and 80 ppb, the average being 35 ppb. The low value indicated that the air is well mixed. No significant differences were found between air masses from the north and from the south. Thus, no significant photochemical pollution problems are expected for the city Osijek.Prikazani su rezultati prvih mjerenja volumnog udjela ozona u Istočnoj Slavoniji tijekom sezone rasta (1. travnja do 30. rujna) 2002. godine. Mjerno mjesto na sjevernoj strani grada Osijeka uz rijeku Dravu na visini od oko 50 m iznad tla odabrano je da se mogu razlikovati dva tipa zračnih masa: ruralno-močvarne sa sjevera i gradsko-predgradske s juga. Izmjereni satni proscjeci udjela ozona u zraku varirali su od 0 do 80 dijelova u milijardu, a srednja je vrijednost iznosila 35 ppb. Niske vrijednosti ukazuju na dobru izmješanost zraka. Usporedbom vrijednosti uz vjetar iz sjevernog odnosno južnog sektora nisu nađene bitne razlike pa se tako ne očekuju problemi fotokemijskog onečišćenja zraka u gradu Osijeku

Tunneling splittings of vibrationally excited states using general instanton paths

A multidimensional semiclassical method for calculating tunneling splittings in vibrationally excited states of molecules using Cartesian coordinates is developed. It is an extension of the theory by Mil'nikov and Nakamura [$\textit{ J. Chem. Phys.}$ $\textbf{122}$, $124311$ $(2005)$] to asymmetric paths that are necessary for calculating tunneling splitting patterns in multi-well systems, such as water clusters. Additionally, new terms are introduced in the description of the semiclassical wavefunction that drastically improve the splitting estimates for certain systems. The method is based on the instanton theory and builds the semiclassical wavefunction of the vibrationally excited states from the ground-state instanton wavefunction along the minimum action path and its harmonic neighborhood. The splittings of excited states are thus obtained at a negligible added numerical effort. The cost is concentrated, as for the ground-state splittings, in the instanton path optimization and the hessian evaluation along the path. The method can thus be applied without modification to many mid-sized molecules in full dimensionality and in combination with on-the-fly evaluation of electronic potentials. The tests were performed on several model potentials and on the water dimer.Comment: The following article has been submitted to Journal of Chemical Physics. After it is published, it will be found at https://aip.scitation.org/journal/jc

PROBLEMS OF AN ORTHOGRAPHIC DICTIONARY

Pravopisni rječnik može se vidjeti kao skup pravopisno signiftkantnih riječi. Takav rječnik dio je svega jezičnoga sustava. Korištenje elektronskih medija potiče raspravu o normiranu modelu rječnickih podataka. Jedan hipotetički podatkovni model testiran je na Babić-Finka-Moguševu pravopisnom rječniku.The orthographic dictionary is seen as a set of orthographically significant word-forms. Such a dictionary should be treated only as a part of integral language system. The usage of electronic media induced discussion about normalized lexical data model. The latent lexical structure is described by general data classes and joined working headings. That gives the opportunity to the researcher of forming different subsystems according to his own interpretation of general model. The hypothetical data model was tested with Babić-Finka-Moguš orthographic dictionary. The manual was analyzed and transformed to structured data by semiautomatic procedures and SGML mark-up system as a tool. The orthographic manual was interpreted as an element of scientific text sub-corpora. Development and adjustment of relevant corpora linguistic methods provided suitable processing tools in automatized production of dictionary normalized data base

Long-range three-body atom-diatom potential for doublet Li3{}_3

An accurate long-range {\em ab initio} potential energy surface has been calculated for the ground state ${}^2A'$ lithium trimer in the frozen diatom approximation using all electron RCCSD(T). The {\em ab initio} energies are corrected for basis set superposition error and extrapolated to the complete basis limit. Molecular van der Waals dispersion coefficients and three-body dispersion damping terms for the atom-diatomic dissociation limit are presented from a linear least squares fit and shown to be an essentially exact representation of the {\em ab initio} surface at large range