Biomedical subjects

Colin J Marsden

Publications and source records attributed to Colin J Marsden.

4 recordsLinked to original sources

PubMed2006

Reactions of Th and U atoms with C2H2: infrared spectra and relativistic calculations of the metallacyclopropene, actinide insertion, and ethynyl products.

Reactions of laser-ablated Th and U atoms with C(2)H(2) during condensation with excess argon at 7 K give several new product species. The metallacyclopropene, inserted hydride, and actinide ethynyl are identified from isotopic frequencies and relativistic DFT calculations. The higher-energy vinylidine isomer was not observed. These actinide metallacyclopropenes exhibit substantially stronger bonding interactions than found recently for the Pd and Pt metals. In the case of Th(C(2)H(2)) the argon matrix interaction is strong enough to reverse the computed order of states (MR-CISD) in favor of a triplet ground state for the (Ar)(n)(Th(C(2)H(2))) complex. The nature of the electronic interactions between various metal atoms and acetylene is compared and the origin of the particularly strong interaction for U and Th is traced to the higher energy of their 6d orbitals. The ThCCH and UCCH actinide ethynyl products are also observed and characterized by C[triple bond]C stretching modes 38+/-2 cm(-1) lower than acetylene itself.

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PubMed2004

Can density functional methods be used for open-shell actinide molecules? Comparison with multiconfigurational spin-orbit studies.

The geometries, electronic structures, and vibrational frequencies of two isoelectronic compounds PuO(2)(2+) and PuN(2) have been studied in detail at the density functional theory (DFT) and multiconfigurational ab initio levels of theory. Dynamic correlation was taken into account using second-order perturbation theory (CASPT2) and the variational difference-dedicated configuration interaction method for comparison with the results of the DFT study. Spin-orbit effects were included within the framework of an effective uncontracted spin-orbit configuration-interaction method which considers electron correlation effects and spin-orbit coupling on equal footing. The twelve lowest f-f electronic transitions are reported. The electronic ground state of both systems is found to be the Omega=4 component of (3)H(g). We thus disagree with an earlier assignment of the ground state of PuN(2) [E. F. Archibong and A. K. Ray, J. Mol. Struct: THEOCHEM 530, 165 (2000)]. Spin-orbit effects are small on both the geometry and vibrational frequencies of the ground states of PuO(2)(2+) and PuN(2), but they completely change the distribution of electronically excited states. A comparison of results obtained with the two classes of methods allows us to demonstrate that an unambiguous assignment of the electronic ground state and electronic spectra requires the use of multireference methods including spin-orbit coupling. Single-reference methods such as DFT provide a reasonable description of the electronic properties of ground states of these open-shell systems, and therefore also of their structural and vibrational properties. The experimental antisymmetric stretching frequency of matrix-isolated PuN(2) is reproduced well by both CASPT2 and DFT calculations; generalized gradient approximation formulations of DFT are more successful than hybrid versions in this respect. Ground-state properties of UO(2) (2+), UN(2), UO(2), PuO(2) (2+), and PuN(2) are compared and discussed.

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PubMed2004

On the electronic structure of molecular UO2 in the presence of Ar atoms: evidence for direct U-Ar bonding.

Calculations via scalar-relativistic density functional theory (DFT) and ab initio CCSD(T) methodologies are used to explore the possibility of direct interactions between molecular UO2 and Ar atoms. The 3Hg electronic state of UO2, which is an excited state of the isolated molecule, exhibits significant bonding to Ar in the model complexes UO2(Ar) and UO2(Ar)5. The calculated vibrational frequencies of ground-state 3Phiu UO2 and UO2(Ar)5 with an (fphi)1(fdelta)1 electron configuration agree well with the observed frequencies of UO2 in solid neon and solid argon, respectively. The results strongly suggest that the ground electron configuration of UO2 changes from 5f17s1 to 5f2 when the matrix host is changed from neon to argon.

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PubMed2002

The First infrared spectra and quasirelativistic DFT studies of the US, US(2), and US(3) molecules.

Laser-ablated U atoms react with discharged sulfur vapor in excess argon to form the US, US(2), and US(3) molecules, which are identified from matrix infrared spectra using sulfur isotopic substitution. Vibrational frequencies from quasirelativistic DFT calculations support these assignments and provide an insight into the bonding and structure. Unlike linear UO(2), US(2) is bent because of more favorable U(6d)-S(3p) overlap, and US(2) has a 118 +/- 5 degrees (experimental based on isotopic shift) or 121 degrees (calculated (3)B(2) ground state, B3LYP) S-U-S bond angle.

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