Marshall G. Cory

AN INTERMEDIATE NEGLECT OF DIFFERENTIAL OVERLAP TECHNIQUE FOR ACTINIDE COMPOUNDS

An intermediate neglect of differential overlap method for examining the electronic structure of actinide complexes is developed. It is characterized by a basis set obtained from relativistic Dirac–Fock atomic calculations, the inclusion of all one‐center two‐electron integrals, and a parameter set based on molecular geometry and ionization spectra. The model is successful in reproducing the geometries of many small test molecules, especially the hexahalides and tetrahalides of the early actinides. We also investigate the bonding in actinocenes and the photoelectron spectra of pentavalent uranium amide/imide complexes as two diverse examples in which this model can be used to help in understanding and prediction.

The transfer Hamiltonian: a tool for large scale simulations with quantum mechanical forces

Abstract We report a method for the inclusion of accurate quantum mechanical forces in large scale molecular dynamics simulations by defining a transfer Hamiltonian containing only one and two-center terms that are modeled by parametric functions. The parameters of the transfer Hamiltonian are fit such that interatomic forces computed ab initio at the CCSD/DZP level of theory for the reactions C2H6→2CH3, Si2H6→2SiH3, and Si2O7H6→Si(OH)3+SiO(OH)3 are accurately modeled. Use of the transfer Hamiltonian, which is electronic state specific, requires several orders of magnitude less time and disk space than do the ab initio calculations, thus they are suitable for treating the quantum region of multi-scale simulations for systems containing ≈103 atoms.

Magneto-infrared spectra of matrix-isolated NiH and NiH2 molecules and theoretical calculations of the lowest electronic states of NiH2

Two vibronic transitions, 2Δ3/2(v=0)←2Δ5/2(v″=0) and 2Π3/2(v=0)←2Δ5/2(v″=0) at 923 and 2560 cm−1, respectively, were observed for NiH in solid argon (and krypton) at 4 K. These Ω=3/2←Ω=5/2 transitions were shifted and broadened by magnetic fields of up to 4 T. Also, its ground state vibrational frequency has been observed in neon, argon, and krypton matrices. Bands in the 600–2000 cm−1 region were assigned as frequencies of the NiH2 (NiD2, NiHD) molecule. Contrary to earlier ab initio calculations, this assignment implies that the molecule is strongly bent in its ground electronic state. This discrepancy was explored theoretically by considering the lowest triplet (linear) and singlet (bent) states of NiH2. The relative energies of the two states have not been satisfactorily resolved, but the calculated structural and vibrational properties of the singlet state are in good agreement with the observations.

Vibrational and electronic spectra of matrix‐isolated para‐dichlorobenzene radical cations

A new pulsed‐glow discharge technique has been used to generate the radical cations of para‐dichlorobenzene (PDCB) and trap them in an argon matrix at 12 K. Three visible absorption bands with origins at 520.5, 490.6, and 322.4 nm are shown to be consistent with gas‐phase photoelectron results and intermediate neglect of differential overlap/spectroscopy calculations. Resonance Raman and fluorescence spectra compare well with previous gas‐phase electron impact excited emission and freon matrix (77 K) studies. The infrared spectrum of the PDCB cation has been measured for the first time and shows bands at 843, 986, 1110, and 1429 cm−1, all of which correlate well, in intensity, with the 520 nm electronic band. Ab initio self‐consistent‐field level calculations on the PDCB neutral and radical cation species reproduce the spectra well, after scaling is performed. It is shown that, upon ionization, the C–Cl bond force constants and the ring central C–C bond force constants increase, while the force constants ...

Implementation of the IPPP–CLOPPA–INDO/S method for the study of indirect nuclear spin coupling constants and its application to molecules containing tin nuclei

Abstract The inner projection of the polarization propagator, using contributions from localized orbitals, IPPP–CLOPPA, and using the intermediate neglect of the differential overlap model parameterized for spectroscopy, INDO/S, was implemented and used to calculate indirect nuclear spin coupling constants. The resulting model was tested on a group of small- and medium-size model compounds by comparing its performance with that of other semi-empirical methods and experiments where available. It is shown that in general the INDO/S approximation with the use of SN2(0) and 〈rN−3〉 atomic parameters taken from the INDO and AM1 approaches is the most suitable scheme to describe coupling constants. The introduction of atomic parameters for SN2(0) and 〈rN−3〉 in the case of heavy nuclei like Sn, is a critical step. The correction of the bonding beta parameter for this nucleus was also necessary within the INDO/S approximation to improve the accuracy and to better account for indirect relativistic effects. The application of this parameterization was accomplished in a series of tetrastannacyclohexanes and different pathways for coupling transmission were analyzed.

The calculation of thermal rate constants for gas phase reactions: A semiclassical flux-flux autocorrelation function (SCFFAF) approach

A semiclassical approach to the calculation of thermal rate constants, based on the flux–flux autocorrelation function method, is presented with its applications. The autocorrelation function is generated along classical trajectories using a classical interpretation of the Boltzmannized flux operator. The activation energies for considered reactions are calculated using the G2/MP2 procedure. The forces are generated using a new parametrization of the PM3 NDDO Hamiltonian optimized for accurate gradients. Thermal rate constants for hydrogen abstraction from ethane and haloethanes by hydroxyl radical serve as a first test of this approach. Calculated results are in good agreement with cumulative rate constants for all systems considered over a range of temperature including room temperature. The approach is able to distinguish between α and β abstraction with a result for fluoroethane at room temperature that is consistent with the available experiment and trends that are in line with those expected.

A Theoretical Study of the [Fe2(μ – S2)(P(o – C6H4S)3)2]2– Electronic Spectrum

ABSTRACT The absorption spectrum of the [Fe 2 ( μ- S 2 )(P( o- C 6 H 4 S) 3 ) 2 ] 2– complex was examined within the Intermediate Neglect of Differential Overlap model parametrized for spectroscopy using a methodology developed earlier for 2-Fe ferredoxins. We demonstrate here that the low energy UV-visible absorption spectrum of this complex can be interpreted as originating from sulfur-to-iron charge-transfer transitions. The results obtained favor the model of antiferromagnetically coupled d 5 – d 5 Fe atoms over other possibilities, for example the formation of a diamagnetic [Fe(d 6 )- S 2 0 -Fe(d 6 )] complex.