Space Saving Calculation of Symbolic Resultants

We describe an approach to the computation of symbolic resultants in which factors are removed during the course of the calculation, so reducing the stack size required for intermediate expressions and the storage space needed. We apply the technique to three well-established methods for calculating resultants. We demonstrate the advantages of our approach when the resultants are large and show that some otherwise intractable problems can be resolved. In certain cases a significant reduction in the cpu time required to calculate the resultant is also evident.      

A computational analysis of the structural features and reactive behavior of some heterocyclic aromatic N-oxides

An ab initio self-consistent-field molecular orbital analysis of the structural features and reactive behavior of pyridine, pyrazine and some of their N-oxide and nitro derivatives has been carried out. Optimized structures have been computed at the 6-31G^* level, yielding geometries in good agreement with experiment. These structures have been used to compute STO-5G electrostatic potentials and average local ionization energies on the respective molecular surfaces. There is considerable conjugation between the N-oxide groups and the aromatic rings, leading to significant para-quinonoid influence, manifested both in terms of structures and reactive properties. The charge-donor role of the N-oxide group allows the aromatic ring in pyridine N-oxide to be susceptible to electrophiles (at the para position) as well as nucleophiles; however, the rings in the pyrazine oxides are only receptive to the latter. The local ionization energies have permitted predictions of pK_a values for pyrazine N-oxide and p-nitropyridine.     

Baxter algebras and Hopf algebras

By applying a recent construction of free Baxter algebras, we obtain a new class of Hopf algebras that generalizes the classical divided power Hopf algebra. We also study conditions under which these Hopf algebras are isomorphic.

     

Infrared spectra of the ethynyl metal hydrides produced in reactions of laser-ablated Mn and Re atoms with acetylene

The ethynyl metal hydride molecules (HM-C≡CH) are identified in the matrix infrared spectra from reactions of laser-ablated Mn and Re atoms with acetylene using D and (13)C isotopic substitution and density functional computed frequencies. The assignment of strong M-H as well as C≡C bond stretching product absorptions suggests oxidative C-H insertion during reagent codeposition and subsequent photolysis. The unique linear structure calculated for HMn-C≡CH is parallel to C(3v) structures found recently for Mn complexes including CH(3)-MnF.     

Infrared spectrum of the CH3OCH2 radical in solid argon

The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 ? shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.     

Matrix infrared spectra and theoretical studies of thorium oxide species: ThOx and Th2Oy

Infrared spectra of three new thorium oxide species have been obtained in argon and neon matrixes. All of the products are experimentally characterized using isotopic oxygen samples with the aid of electronic structure calculations. Ground state thorium atoms react with O(2) to form the ThO(2) molecules, which can dimerize to give Th(2)O(4) products. Th(2)O(4) is predicted to have nonplanar C(2h) symmetry for its closed shell singlet ground state. The rhombus-shaped Th(2)O(2) molecule in the (1)A(g) (D(2h)) ground state is also observed and its formation is proposed via the reaction of Th(2) with O(2). In addition, electron capture of neutral thorium dioxide results in the formation of the ThO(2)(-) anion. It is predicted to have a doublet ground state with a geometry similar to that of the neutral ThO(2) molecule. Electronic structure calculations on the unobserved Th(2)O and Th(2)O(3) molecules are also provided.