Biomedical subjects

Justin M Turney

Publications and source records attributed to Justin M Turney.

3 recordsLinked to original sources

PubMed2006

Characterization of singlet ground and low-lying electronic excited states of phosphaethyne and isophosphaethyne.

The singlet ground ((approximate)X(1)Sigma1+) and excited (1Sigma-,1Delta) states of HCP and HPC have been systematically investigated using ab initio molecular electronic structure theory. For the ground state, geometries of the two linear stationary points have been optimized and physical properties have been predicted utilizing restricted self-consistent field theory, coupled cluster theory with single and double excitations (CCSD), CCSD with perturbative triple corrections [CCSD(T)], and CCSD with partial iterative triple excitations (CCSDT-3 and CC3). Physical properties computed for the global minimum ((approximate)X(1)Sigma+HCP) include harmonic vibrational frequencies with the cc-pV5Z CCSD(T) method of omega1=3344 cm(-1), omega2=689 cm(-1), and omega3=1298 cm(-1). Linear HPC, a stationary point of Hessian index 2, is predicted to lie 75.2 kcal mol(-1) above the global minimum HCP. The dissociation energy D0[HCP((approximate)X(1)Sigma+)-->H(2S)+CP(X2Sigma+)] of HCP is predicted to be 119.0 kcal mol(-1), which is very close to the experimental lower limit of 119.1 kcal mol(-1). Eight singlet excited states were examined and their physical properties were determined employing three equation-of-motion coupled cluster methods (EOM-CCSD, EOM-CCSDT-3, and EOM-CC3). Four stationary points were located on the lowest-lying excited state potential energy surface, 1Sigma- -->1A", with excitation energies Te of 101.4 kcal mol(-1) (1A"HCP), 104.6 kcal mol(-1)(1Sigma-HCP), 122.3 kcal mol(-1)(1A" HPC), and 171.6 kcal mol(-1)(1Sigma-HPC) at the cc-pVQZ EOM-CCSDT-3 level of theory. The physical properties of the 1A" state with a predicted bond angle of 129.5 degrees compare well with the experimentally reported first singlet state ((approximate)A1A"). The excitation energy predicted for this excitation is T0=99.4 kcal mol(-1) (34 800 cm(-1),4.31 eV), in essentially perfect agreement with the experimental value of T0=99.3 kcal mol(-1)(34 746 cm(-1),4.308 eV). For the second lowest-lying excited singlet surface, 1Delta-->1A', four stationary points were found with Te values of 111.2 kcal mol(-1) (2(1)A' HCP), 112.4 kcal mol(-1) (1Delta HPC), 125.6 kcal mol(-1)(2(1)A' HCP), and 177.8 kcal mol(-1)(1Delta HPC). The predicted CP bond length and frequencies of the 2(1)A' state with a bond angle of 89.8 degrees (1.707 A, 666 and 979 cm(-1)) compare reasonably well with those for the experimentally reported (approximate)C(1)A' state (1.69 A, 615 and 969 cm(-1)). However, the excitation energy and bond angle do not agree well: theoretical values of 108.7 kcal mol(-1) and 89.8 degrees versus experimental values of 115.1 kcal mol(-1) and 113 degrees. of 115.1 kcal mol(-1) and 113 degrees.

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PubMed2005

Does GaH5 exist?

The existence or nonexistence of GaH(5) has been widely discussed [N. M. Mitzel, Angew. Chem. Int. Ed. 42, 3856 (2003)]. Seven possible structures for gallium pentahydride have been systematically investigated using ab initio electronic structure theory. Structures and vibrational frequencies have been determined employing self-consistent field, coupled cluster including all single and double excitations (CCSD), and CCSD with perturbative triples levels of theory, with at least three correlation-consistent polarized-valence-(cc-pVXZ and aug-cc-pVXZ) type basis sets. The X (1)A(') state for GaH(5) is predicted to be weakly bound complex 1 between gallane and molecular hydrogen, with C(s) symmetry. The dissociation energy corresponding to GaH(5)-->GaH(3)+H(2) is predicted to be D(e)=2.05 kcal mol(-1). The H-H stretching fundamental is predicted to be v=4060 cm(-1), compared to the tentatively assigned experimental feature of Wang and Andrews [J. Phys. Chem. A 107, 11371 (2003)] at 4087 cm(-1). A second C(s) structure 2 with nearly equal energy is predicted to be a transition state, corresponding to a 90 degrees rotation of the H(2) bond. Thus the rotation of the hydrogen molecule is essentially free. However, hydrogen scrambling through the C(2v) structure 3 seems unlikely, as the activation barrier for scrambling is at least 30 kcal mol(-1) higher in energy than that for the dissociation of GaH(5) to GaH(3) and H(2). Two additional structures consisting of GaH(3) with a dihydrogen bond perpendicular to gallane (C(3v) structure 4) and an in-plane dihydrogen bond [C(s)(III) structure 5] were also examined. A C(3v) symmetry second-order saddle point has nearly the same energy as the GaH(3)+H(2) dissociation limit, while the C(s)(III) structure 5 is a transition structure to the C(3v) structure. The C(4v) structure 6 and the D(3h) structure 7 are much higher in energy than GaH(3)+H(2) by 88 and 103 kcal mol(-1), respectively.

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PubMed2005

The singlet electronic ground state isomers of dialuminum monoxide: AlOAl, AlAlO, and the transition state connecting them.

The singlet electronic ground state isomers, X (1)Sigma(g) (+) (AlOAl D(infinityh)) and X (1)Sigma(+) (AlAlO C(infinitynu)), of dialuminum monoxide have been systematically investigated using ab initio electronic structure theory. The equilibrium structures and physical properties for the two molecules have been predicted employing self-consistent field (SCF) configuration interaction with single and double excitations (CISD), multireference CISD (MRCISD), coupled cluster with single and double excitations (CCSD), CCSD with perturbative triples [CCSD(T)], CCSD with iterative partial triple excitations (CCSDT-3 and CC3), and full triples (CCSDT) coupled cluster methods. Four correlation consistent polarized valence (cc-pVXZ) type basis sets were used. The AlAlO system is rather challenging theoretically. The two isomers are confirmed to have linear structures at all levels of theory. The symmetric isomer AlOAl is predicted to lie 81.9 kcal mol(-1) below the asymmetric isomer AlAlO at the cc-pV(Q+d)Z CCSD(T) level of theory. The predicted harmonic vibrational frequencies for the X (1)Sigma(g) (+) AlOAl molecule, omega(1)=517 cm(-1), omega(2)=95 cm(-1), and omega(3)=1014 cm(-1), are in good agreement with experimental values. The harmonic vibrational frequencies for the X (1)Sigma(+) AlAlO structure, omega(1)=1042 cm(-1), omega(2)=73 cm(-1), and omega(3)=253 cm(-1), presently have no experimental values with which to be compared. With the same methods the barrier heights for the isomerization AlOAl-->AlAlO and AlAlO-->AlOAl reactions were predicted to be 84.3 and 2.4 kcal mol(-1), respectively. The dissociation energies D(0) for AlOAl (X (1)Sigma(g) (+)) and AlAlO (X (1)Sigma(+))-->AlO (X (2)Sigma(+))+Al ((2)P) were determined to be 130.8 and 48.9 kcal mol(-1), respectively. Thus, both symmetric AlOAl (X (1)Sigma(g) (+)) and asymmetric AlAlO (X (1)Sigma(+)) isomers are expected to be thermodynamically stable with respect to the dissociation into AlO (X (2)Sigma(+)) + Al ((2)P) and kinetically stable for the isomerization reaction (AlAlO-->AlOAl) at sufficiently low temperatures.

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