Why do the second row transition metal atoms prefer 5s14dm+1 to 5s24dm?

Numerical Hartree-Fock (NHF) calculations have been performed for 332 ground and low-lying excited states of the fifth period atoms Rb through Xe, with our special interest in the states arising from the 5s ²4d ^m , 5s ¹4d ^m +1, and 5s ⁰ 4d ^m +2 configurations of the second row transition metal atoms. Among various properties, orbital energies and mean values ofr of the outermost orbitals of each symmetry are presented as well as total energies. It is discussed in some detail why the second row transition metal atoms have a tendency to prefers ¹ d ^m +1 as the ground configuration in contrast to the preferreds ² d ^m configuration in the first row transition metal atoms. Our systematic NHF computations reported in this and the previous papers conclude that the Hartree-Fock method correctly predicts the experimental ground state of the atoms He through Xe with the sole exception for Zr.     

Fine-structure analysis of the (5d+6s)5 levels of Ta I

The fine structure of the prominent even levels of the neutral tantalum atom has been analyzed by simultaneous parametrization of one- and two-body interactions for the model space (5d+6s)⁵. The analysis was stimulated by the current discovery of several energy levels. It was possible to clear the configurations and designations of the energy levels given in commonly used tables. Magnetic-dipole hyperfine interaction constants A and electric-quadrupole hyperfine interaction constants B were calculated using the calculated eigenfunctions and adjusting radial integrals in a least-squares procedure which compares the calculated Aand B-constants with the experimental values. The rms error of this fitting procedure confirms the quality of the fine structure analysis. Moreover, wavenumbers and hyperfine constants of 52 further levels, up to now unidentified, are predicted.     

Stereocontrolled synthesis of (5+5), (5+6) and (6+6) 3-spiropseudonucleosides

3-Spiropseudonucleosides, in which the heterocyclic base is a five-membered (oxazolidine, imidazolidine, thiohydantoin) or six-membered (perhydrooxazine) heterocycle, have been prepared starting from a hexofuranos-3-ulose. The method leads to good yields and is completely stereoselective. The key intermediate is a sugar iso(thio)cyanate.     

Hyperfinestructure-investigations in the mangan I configurations 3d 5 4s 4p and 4s 5s

Nine transitions (ranging from 475 till 733 nm) between the excited configuration 3d ⁵ 4s 5s and 3d ⁵ 4s 4p of⁵⁵Mn were investigated with computer supported interference spectroscopy. Thus the hyperfine structure (hfs) of the four 4s 5s and the twelve 4s 4p levels is now completely known from experiment. The hfs results are discussed with the effective operator technique and for 4s 4p the accuracy of the one-electron parametersa ^ik could be improved:a _3d ¹⁰ =?6.28(24),a _4s ¹⁰ =154.0(1.4),a _4p ⁰¹ =9.3(8),a _4p ¹² =7.7(2.5) in mK. For the configuration 4s 5s — for which fine structure calculations are not yet available — the experimental hfs data prove a practically pureS-character. Besides the one-electron splitting parameters deduced:a _3d ¹⁰ =?6.5(5),a _4s ¹⁰ =182(3),a _5s ¹⁰ =24(3) in mK, permit to determine the degree of mixing between the twoe ⁶ S _5/2 andf ⁶ S _5/2 levels which amounts to about 3%.     

Importance of the methyl group at C10 of squalene for hopene biosynthesis and novel carbocyclic skeletons with 6/5 + 5/5 + (6) ring system(s)

[reaction: see text] Incubation of (6E,10E,14E,18E)-2,6,10,19,23-pentamethyl-tetracosa-2,6,10,14,18,22-hexaene with Alicyclobacillus acidocaldarius hopene cyclase afforded four products having two types of carbocyclic skeletons, i.e., two hopane products and two products having an unprecedented carbocyclic skeleton of 6/5 + 5/5 +6 pentacyclic and 6/5 + 5/5 tetracyclic ring systems. The former two hopane skeletons were formed from the bioconversion of C15-desmethylsqualene and the latter two skeletons from that of C10-desmethylsqualene.     

L-shell ionization in Au by O5+-and Ni5+-ion impact

TheL X-ray production cross sections in gold by 60 to 72 MeV O⁵⁺ ions and 58 to 87 MeV Ni⁵⁺-ions have been measured. TheL-subshell ionization cross sections derived from these experimental results have been compared with the direct ionization theories viz. plane wave Born approximation (PWBA) theory and modified perturbed-stationary-state theory with energy loss, Coulomb deflection and relativistic effects (MECPSSR). A new procedure has been described to account for the change in the yield ratioLβ₁/Lβ_{2, 15} with energy, for Ni⁵⁺-ion impact on gold. TheL sub-shell ionization cross sections have been derived fromLβ₁,Lβ₄ andLβ_{2, 15} lines of theLβ group in addition to those calculated by the conventional Datz TRY3 technique usingLα,Lγ₁ andLγ_{2, 3} X-ray lines. From the shift in the energies of variousL X-ray lines and changes in their intensities, 3 and 5 spectator vacancies in theM- andN-shells in gold have been estimated with O⁵⁺-ion impact while 7, 20 and 4 to 6 spectator vacancies have been inferred in theM-,N-andO-shells respectively with Ni⁵⁺-ion impact in the energy range of the projectiles undertaken in the present studies.     

The diatropic sigma ring currents of [pi2s + pi2s + pi2s] pericyclic transition states

Ab initio current-density maps for the (4n + 2)-electron transition states of two thermally allowed [pi2s + pi2s + pi2s] trimerisations, of ethyne to benzene (1), and of ethene to cyclohexane (2), show that both support sigma diatropic ring currents, dominated by four-electron sigma --> sigma* virtual excitation of HOMO electrons.     

Electric conductivity of RbFeO2 modified with Nb5+ and Ta5+ cations

Solid solutions based on RbFeO₂ in Rb_{2 ? 2x} Fe_{2 ? x} Nb(Ta) _x O₄ (0 ?? x ?? 0.2) systems were synthesized. Their crystal structure and the temperature and concentration dependences of the total and ion conductivities were studied. The ranges of composition and temperature with dominant rubidium-cation conductivity were determined. For the Rb_1.9Fe_1.95Ta_0.05O₄ solid solution, the rubidium-cation conductivity was found to be 2.3 × 10^?2 S/cm at 200°C, which exceeds the electric conductivity of other known polycrystalline rubidium-cation solid electrolytes.     

The 5s5p 3 levels of Sn I

We report a re-examination of the fine structure analysis of the levels of the 5s5p ³ configuration of Sn I taking into account the perturbing effects of twenty-two configurations of the type 5s ²5pmd and 5s ²5pns and utilizing recent experimental data. New identifications of levels of 5s5p ³ are proposed and reasons for their assignment are presented.     

Vibrational predissociation of H5 +

The full nine-dimensional vibrational Hamiltonian for H5 + described in the literature [Kraemer et al., J. Mol. Spectrosc. 164, 500 (1994)] is adopted here for an approximate evaluation of the spectral linewidths of the observed H-H stretching modes of the H5 + ion and the corresponding modes of its D5 + isotopomer. In this approximation the high dimensionality of the original Hamiltonian is reduced to a three-dimensional model Hamiltonian which takes only the H-H stretching modes and the molecular dissociation mode into consideration assuming that they are adiabatically separable from the remaining modes. To make the calculations numerically feasible, the molecular degenerate ("skeletal") vibrations are assumed to take place in harmonic potentials, and the effect of the internal propeller rotation is completely disregarded. The linewidths calculated in this approximation are too small to explain the broad shapes of the observed spectral transitions. It can thus be argued that the failure to resolve rotational structure in the observed bands is mainly due to spectral congestion and only partly due to predissociation of the H5 + cluster.     

Transition metal-catalyzed intermolecular [5+2] and [5+2+1] cycloadditions of allenes and vinylcyclopropanes

Initial examples of the intermolecular Rh(I)-catalyzed [5+2] cycloaddition reaction of bifunctional allenes and vinylcyclopropanes are described. The reactions proceed with facility and in yields of up to 99% with a variety of alkyne-, ester-, styrene-, or cyano-substituents on the allene to afford the corresponding cycloadducts. In the presence of CO, the reaction proceeds to an eight-membered ring cycloadduct and its transannularly closed product, providing the first example of a three-component [5+2+1] cycloaddition with allenes.     

Precision energies and hyperfine structures of the 5s5p 3 P 0,1,2 0 and 5s6s 3 S 1 levels in In II

Absolute frequencies of hyperfine components of the 230.6 nm (5s ^{2 1} S ₀?5s5p ³ P ₁ ⁰ ), 193.6 nm (5s5p ³ P ₀ ⁰ ?5s6s ³ S ₁), 197.7 nm (5s5p ³ P ₁ ⁰ ?5s6s ³ S ₁) and 207.9 nm (5s5p ³ P ₂ ⁰ ?5s6s ³ S ₁) transitions in In II emitted from a hollow-cathode source have been measured using a high-resolution, scanning échelle monochromator. The measured frequencies of these four transitions have been used to determine the energies and hyperfine interaction constants of the 5s5p ³ P ₀ ⁰ ,³ P ₁ ⁰ ,³ P ₂ ⁰ and 5s6s ³ S ₁ levels in In II. The hyperfine interaction constants for the dominant isotope¹¹⁵In are found to be: 5s5p ³ P ₁ ⁰ A=0.2322(2) cm^?1,B=?0.0159(9) cm^?1 5s5p ³ P ₂ ⁰ A=0.1699(4) cm^?1,B= 0.021 (6) cm^?1 5s6s ³ S ₁ A=0.4022(4) cm^?1,B= 0.002 (2) cm^?1. The absolute frequency of the very narrow, strongly forbidden In II 236.5 nm (5s ^{2 1} S ₀?5s5p ³ P ₀ ⁰ ) transition, which has been proposed as a candidate for a new optical frequency standard, is found to be 42275.986(7) cm^?1.     

Fine structure of the 1s5f and 1s5g levels of He I

The fine structure of the 1s5f and 1s5g levels of He I was measured using microwave spectroscopy. The helium atoms were excited by ion impact, and the eleven allowed 1s5f ^2S+1 F _J –1s5g ^2S′+1 G _J , transitions near ν≈15 GHz were induced and detected by measuring the 1s4d–1s2p or 1s3d–1s2p spectral-line intensities of the impact radiation as a function of the microwave frequency. The measured transition frequencies are in accord with theoretical values and, except for one transition frequency, with earlier experimental data. The existing discrepancy between these earlier data and theory could be solved.     

Preparation of polarized excited rare gas atom statesR(np 5(n+1)s) andR(np 5(n+1)p) by laser optical pumping

On the basis of rate equations we have theoretically analyzed all optical pumping schemes, which arise from the rare gas transitionsR(np ⁵(n+1)s,J _i =0, 2) toR(np ⁵(n+1)p,J _f =1, 2, 3) for linearly, circularly and unpolarized light propagating in one direction. Analytical formulae are given for the time-averaged or steady state populations of the magnetic substates and their state multipoles, as a function of the partial decay rateA _fi , the natural lifetime τ of the upper level, and the laser induced pumping rateb. Numerical values of these quantities are presented for the case of actual interestR=Ne.