K. Balasubramanian

University of California, Berkeley, Berkeley, California, United States

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Publications (336)648.12 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: MCM-41-type mesoporous silica functionalized with the CMPO-based 'Ac-Phos' silane has been reported in the literature (1) to show good capacity as an acftinide sorbent material, with potential applications in environmental sequestration, aqueous waste separation and/or vitrification, and chemical sensing of actinides in solution. The study explores the complexation of Pu(IV and VI) and other selected actinides and lanthanides by SBA-15 type mesoporous silica functionalized with Ac-Phos. The Pu binding kinetics and binding capacity were determined for both the Ac-Phos functionalized and unmodified SBA-15. They analyzed the binding geometry and redox behavior of Pu(VI) by X-ray absorption spectroscopy (XAS). They discuss the synthesis and characterization of the functionalized mesoporous material, batch sorption experiments, and the detailed analyses of the actinide complexes that are formed. Structural measurements are paired with high-level quantum mechanical modeling to elucidate the binding mechanisms.
    10/2010
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    Ping Yi Feng, Dingguo Dai, K. Balasubramanian
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    ABSTRACT: We have computed the optimized geometries and energy separations for the electronic states of Al3As2, Al2As3, and their positive and negative ions using complete active-space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction (MRSDCI) calculations which included up to 3.9 million configurations. The 2A1(C2v) state is the lowest electronic state of Al3As2 among seven states with distorted trigonal bipyramid structures. The 2A1 state and another distorted 2B1(C2v) state are formed from the undistorted 2E‘ and 2E‘ ‘(D3h) states, respectively, as a consequence of Jahn−Teller effect. The 2A2‘ ‘(D3h) state is found to be the ground state of Al2As3 with an undistorted trigonal bipyramid structure (D3h). Four electronic states of Al3As2+ and Al2As3+ were computed and their ground states are undistorted 3A2‘ and 1A1‘(D3h) states for Al3As2+ and Al2As3+, respectively. The 1A1‘(D3h) state is the ground state for both Al3As2- and Al2As3-. The atomization energies, adiabatic ionization potentials, and other properties for the electronic states of Al3As2 and Al2As3 and a comparison with the Ga analogues are provided. The Al3As2 cluster is shown to differ from Ga3As2 in some states due to a greater charge transfer from Al(3s) to As(4p) in Al3As2.
    ChemInform 05/2010; 31(18).
  • ChemInform 01/2010; 30(10).
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 26(2).
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    K. Balasubramanian, Ping Yi Feng
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    ABSTRACT: Complete active-space self-consistent field (CASSCF) method followed by multireference singles + doubles configuration interaction (MRSDCI) calculations that included up to 4 million configurations were carried out on the electronic states of Al3P2, Al2P3 and their anions and cations. Our computed results explain the recently reported anion photoelectron spectra of Al2P3- and Al3P2- by Neumark and co-workers.1 We find that both the Al2P3- and Al2P3 species have D3h undistorted trigonal bipyramidal structures consistent with the sharp and intense ground-state peak in the observed spectra. But the neutral Al3P2 cluster was found to be Jahn−Teller distorted in contrast to the Al3P2- anion, which has a D3h undistorted trigonal bipyramidal structure, consistent with the observed extended vibrational progression of the X state of the spectra. Our computed electron affinities agree well with the onsets of the observed X peaks in both spectra. We assign the partially resolved vibrational structure in the observed spectra to the totally symmetric stretch mode than to symmetry lowering of Al2P3, which is found to be in a 2A2‘ ‘ (D3h) state and cannot undergo Jahn−Teller distortion. Seven electronic states of Al3P2 are computed, among which the 2A1(C2v) state is the ground state with a distorted trigonal bipyramid structure. The distorted2A1 and 2B1 (C2v) states are identified as Jahn−Teller components of the undistorted 2E‘ and 2E‘ ‘ (D3h) states, respectively. Properties of four electronic states of Al2P3, Al3P2+, and Al2P3+ are also reported. The ground states of both Al3P2+ and Al2P3+ are undistorted 3A2‘ and 1A1‘, respectively (D3h symmetry). The atomization energy, adiabatic ionization potentials, dipole moments, and other properties for the electronic states of Al3P2 and Al2P3 are calculated and discussed. Comparisons are made with the Ga and In analogues of these species.
    ChemInform 01/2010; 33(8).
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    Zhiji Cao, K. Balasubramanian
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    ABSTRACT: Extensive ab initio calculations have been carried out to study equilibrium structures, vibrational frequencies, and the nature of chemical bonds of hydrated UO2(OH)+, UO2(OH)2, NpO2(OH), and PuO2(OH)+ complexes that contain up to 21 water molecules both in first and second hydration spheres in both aqueous solution and the gas phase. The structures have been further optimized by considering long-range solvent effects through a polarizable continuum dielectric model. The hydrolysis reaction Gibbs free energy of UO2(H2O)52+ is computed to be 8.11 kcal/mol at the MP2 level in good agreement with experiments. Our results reveal that it is necessary to include water molecules bound to the complex in the first hydration sphere for proper treatment of the hydrated complex and the dielectric cavity although water molecules in the second hydration sphere do not change the coordination complex. Structural reoptimization of the complex in a dielectric cavity seems inevitable to seek subtle structural variations in the solvent and to correlate with the observed spectra and thermodynamic properties in the aqueous environment. Our computations reveal dramatically different equilibrium structures in the gas phase and solution and also confirm the observed facile exchanges between the complex and bulk solvent. Complete active space multiconfiguration self-consistent field followed by multireference singles+doubles CI (MRSDCI) computations on smaller complexes confirm predominantly single-configurational nature of these species and the validity of B3LYP and MP2 techniques for these complexes in their ground states.
    The Journal of Chemical Physics 10/2009; 131(16). · 3.12 Impact Factor
  • K Balasubramanian, Zhiji Cao
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    ABSTRACT: A relativistic complete active space multiconfigurational self-consistent field followed by multireference singles + doubles configuration interaction computations are carried out on the potential energy surfaces of electronic states of CmH(2) and CmH(2)(+) for the insertion reaction of Cm and Cm(+) into H(2). We have also carried out corresponding computations on several electronic states of CmH and CmH(+). Moreover, multireference relativistic configuration interaction computations including spin-orbit coupling were carried out on 75 electronic states of CmH(+), which were found to be below the 45 000 cm(-1) region. We have computed the first ionization energy of Cm as 5.94 eV in excellent agreement with experimental value of 5.99 eV. Our computations reveal barriers for the insertion of Cm and Cm(+) in their ground electronic states into H(2), but once the barriers are surmounted, both Cm + H(2) and Cm(+) + H(2) form stable products. The potential energy curves of CmH and CmH(+) reveal the existence of several low-lying open-shell excited states with varied Lambda quantum numbers and spin multiplicities. The excited states of these species exhibit intermediate coupling, although the spin-orbit splittings of the (9)Sigma(-) and (8)Sigma(-) ground states of CmH and CmH(+) are small, exhibiting nearly inverted multiplets.
    The Journal of Physical Chemistry A 10/2009; 113(45):12512-24. · 2.77 Impact Factor
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    ABSTRACT: We have carried out both time-resolved laser fluorescence spectroscopic and computational studies on the complexes of curium(III) with multidentate Phosphonopropionic (PPA) acid ligands. A number of complexes of Cm(III) with these ligands, such as CmH(2)PPA(2+), CmHPPA(+), Cm[H(2)PPA](2)(+), and Cm[HPPA](2)(-) have been studied. Our computational studies focused on all possible isomers in the gas phase and aqueous solution so that the relative binding strengths of carboxylic versus phosphoric groups can be assessed in these multidentate systems. The solvation effects play an important role in the determination of the preferred configurations and binding propensities of carboxylate versus phosphate sites of the ligands. Our computations assess the relative strengths of single and multidentate complexes in solutions for these systems. The computed free energies of solvation explain the experimentally observed fluorescence spectra and the lifetimes of these complexes in that as more water molecules are displaced from the first hydration sphere by the ligands that bind to Cm(III), the fluorescence lifetime increases. We have found that the most stable complex for CmH(2)PPA(2+) in the aqueous phase exhibits a monodentate complex where the curium(III) is bound to the deprotonated phosphate oxygen atom. Our computations support the observed longer fluorescence lifetime of CmH(2)PPA(2+) (112 mus) compared to the free Cm(III) aquo ion (65 mus), suggesting a greater degree of H(2)O displacement from the hydration sphere. For the Cm-HPPA(+) complex, we find a tridentate form as the most stable structure which supports the observed fluorescence lifetime for the CmHPPA(+) complex (172 mus), confirming the removal of up to six water molecules from the inner hydration sphere. The relative stabilities of the complexes are found to vary substantially between the gas phase and solution, indicating a major role of solvation in the relative stabilities of these complexes.
    Inorganic Chemistry 09/2009; 48(20):9700-14. · 4.59 Impact Factor
  • K Balasubramanian, Zhiji Cao
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    ABSTRACT: Extensive ab inito computations have been carried out to study the equilibrium structure, infrared spectra, and bonding characteristics of a variety of hydrated NpO2(CO3)m(q-) complexes by considering the solvent as a polarizable dielectric continuum as well as the corresponding anhydrate complexes in the gas phase. The computed structural parameters and vibrational results at the MP2 level in aqueous solution are in good agreement with Clark et al.'s experiments and provide realistic pictures of the neptunyl complexes in an aqueous environment. Our computed hydration energies reveal that the complex with water molecules directly bound to it yields the best results. Our analysis of the nature of the bonding of neptunyl complexes provides insight into the nature of 6d and 5f bonding in actinide complexes.
    Inorganic Chemistry 01/2008; 46(25):10510-9. · 4.59 Impact Factor
  • ZHIJI CAO, KRISHNAN BALASUBRAMANIAN
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    ABSTRACT: Spectroscopic properties of the low-lying electronic states of In3N, InN3, and their ions are computed by the complete active-space self-consistent field (CASSCF) followed by multireference singles + doubles configuration interaction (MRSDCI) calculations. Our results predict that the spectra of In3N/InN3 are substantially different from those of Ga3As/GaAs3 and Al3P/AlP3 tetramers. The ground state of In3N is a closed-shell 1A′1 state with a planar D3h symmetry, whereas the ground state of InN3 is a 1Σ+ state of linear In–N–N–N structure. The equilibrium geometries, vibrational frequencies, atomization energies, adiabatic ionization potentials, electron affinities, and other properties are discussed.
    Journal of Theoretical and Computational Chemistry 01/2008; 07(04). · 0.52 Impact Factor
  • K. Balasubramanian, Doyel Chaudhuri
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    ABSTRACT: We have computed the structures, and select vibrational spectra, electron density and molecular orbital contour plots of plutonium(VI) complexes of environmental importance such as [PuO2(CO3)2]2− and [PuO2(CO3)3]4−. We show that Ca2+ is efficacious in gas-phase modeling of electronic and spectroscopic properties of multiply charged plutonyl di and tricarbonate anions through complexes such as PuO2(CO3)2Ca and [PuO2(CO3)3Ca3]2+.
    Chemical Physics Letters 01/2008; 450(4):196-202. · 2.15 Impact Factor
  • Bingbing Suo, Krishnan Balasubramanian
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    ABSTRACT: The potential energy curves of the low-lying electronic states of yttrium carbide (YC) and its cation are calculated at the complete active space self-consistent field and the multireference single and double excitation configuration interaction (MRSDCI) levels of theory. Fifteen low-lying electronic states of YC with different spin and spatial symmetries were identified. The X (4)Sigma- state prevails as the ground state of YC, and a low-lying excited A (4)Pi state is found to be 1661 cm(-1) higher at the MRSDCI level. The computations of the authors support the assignment of the observed spectra to a B (4)Delta(Omega=72)<--A (4)Pi(Omega=52) transition with a reinterpretation that the A (4)Pi state is appreciably populated under the experimental conditions as it is less than 2000 cm(-1) of the X (4)Sigma- ground state, and the previously suggested (4)Pi ground state is reassigned to the first low-lying excited state of YC. The potential energy curves of YC+ confirm a previous prediction by Seivers et al. [J. Chem. Phys. 105, 6322 (1996)] that the ground state of YC+ is formed through a second pathway at higher energies. The calculated ionization energy of YC is 6.00 eV, while the adiabatic electron affinity is 0.95 eV at the MRSDCI level. The computed ionization energy of YC and dissociation energy of YC+ confirm the revised experimental estimates provided by Seivers et al. although direct experimental measurements yielded results with greater errors due to uncertainty in collisional cross sections for YC+ formation.
    The Journal of Chemical Physics 07/2007; 126(22):224305. · 3.12 Impact Factor
  • K. Balasubramanian, Zhiji Cao
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    ABSTRACT: We have computed the torsional tunneling barriers for water molecules bound to actinyl ions, UO22+, NpO2+, and PuO22+ using high-level relativistic computations in aqueous solution. We show that the barriers drop substantially as a function of number of water molecules, which could assist facile exchange of water molecules from the solvent to the complex. Our findings are consistent with the 17O dynamical NMR studies of Farkas et al.
    Chemical Physics Letters 01/2007; 433(s 4–6):259–263. · 2.15 Impact Factor
  • Zhiji Cao, Krishnan Balasubramanian
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    ABSTRACT: Twenty electronic states of In2N2 are computed using a complete active space multi-configuration self-consistent field followed by multi-reference singles+doubles configuration interaction (MRSDCI) computations. In contrast to other III–V tetramers, In2N2 exhibits nearly degenerate T-shaped triplet states and linear In–In–N–N 3Σ− state. The 1Ag state with a rhombus structure was found to be 0.94eV higher. Our computations show that anion photodetachment spectra of In2N2 could be substantially different from the spectra of Ga2P2 and related tetramers observed by Neumark and coworkers. The computed vibrational and Raman spectra are provided.
    Chemical Physics Letters 01/2007; 439(4):288-295. · 2.15 Impact Factor
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    Krishnan Balasubramanian
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    ABSTRACT: Octanitrocubane is shown to possess interesting nuclear spin statistics and rovibronic level patterns in its equilibrium chiral (D4) symmetry both due to 17O and 14N nuclear spin species. The populations and distributions of rovibronic levels will be influenced by the chiral symmetry and the nuclear spin species and spin statistical weights due to 17O, 14N and 13C species. We have computed the nuclear spin species and spin statistics and correlations of the rovibronic levels and spin species in different symmetries. Our predicted results could aid in the interpretation of 17O dynamic NMR, vibronic and rovibronic spectra of gas-phase octanitrocubane.
    Chemical Physics Letters 01/2007; 441(1):29-38. · 2.15 Impact Factor
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    ABSTRACT: We have computed the electronic structural and spectroscopic properties for the low-lying electronic states of plutonium hydrides, PuHn (n=2–4) and their ions which provide significant insight into plutonium hydriding reactions. We have employed a relativistic quantum technique that uses relativistic effective core potentials on Pu. Our computations show that whereas PuH2 and PuH3 form stable C2v and C3v structures which exhibit Pu–H direct chemical bonds, PuH4 becomes a complex of PuH2 with a partially dissociated H2. Our computations show that the H2 dissociation is assisted by PuH2. Electron density contour maps including Laplacians of charge densities support that the Pu site of the hydrided species is depleted substantially in charge thereby causing catalysis of further hydriding. The IR spectra show that the H2 sorbed on PuH2 is partially dissociated. We have also provided comparison of our results with corresponding computations on uranium hydrides.
    Journal of Alloys and Compounds 01/2007; 444:447-452. · 2.73 Impact Factor
  • Guang-hui Chen, Krishnan Balasubramanian
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    ABSTRACT: Electronic states of the GeC2N radical are explored at various theoretical levels including complete active space multi-configuration self-consistent field followed by complete active space perturbation computations. Ten minimal energy isomers and 10 interconversion transition states are found. The thermodynamically most stable isomer is a linear form GeCCN 1 which is qualitatively described as a resonance hybrid of ∣GeCCN∣, ∣GeC-CN∣, and ∣GeCCN∣ forms, with the second one contributing to a greater extent suggestive of a radical adduct between GeC and CN. The second low-lying linear isomer GeCNC 2 (21.9kcal/mol) has resonating structures ∣GeC-NC∣, ∣GeCNC∣, and ∣GeCN–C∣.
    Chemical Physics Letters 01/2007; 438(4):162-168. · 2.15 Impact Factor
  • Zhiji Cao, Bingbing Suo, K. Balasubramanian
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    ABSTRACT: Potential energy curves of low-lying electronic states of InN2, In2N, and their cations and anions are investigated by the complete active space multi-configuration self-consistent field (CASSCF) followed by multi-reference singles + doubles configuration interaction (MRSDCI) computations. The neutral InN2 and In2N exhibit linear 2Π and 2Σu+ ground states, respectively. The InNN+ cation exhibits a linear C∞v ground state whereas In2N+ ion exhibits two nearly-degenerate singlet and triplet ground states. Whereas In2N− is strongly bound with an adiabatic electron affinity of 2.07eV, the electron affinity of InNN is only 0.2eV.
    Chemical Physics Letters 12/2006; 432(1):50-56. · 2.15 Impact Factor
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    Pablo A Denis, K Balasubramanian
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    ABSTRACT: The potential energy curves and spectroscopic constants of the ground and 29 low-lying excited states of MoC with different spin and spatial symmetries within 48 000 cm(-1) have been investigated. We have used the complete active space multiconfiguration self-consistent field methodology, followed by multireference configuration interaction (MRCI) methods. Relativistic effects were considered with the aid of relativistic effective core potentials in conjunction with these methods. The results are in agreement with previous studies that determined the ground state as X (3)Sigma(-). At the MRCISD+Q level, the transition energies to the 1 (3)Delta and 4 (1)Delta states are 3430 and 8048 cm(-1), respectively, in fair agreement with the results obtained by DaBell et al. [J. Chem. Phy. 114, 2938 (2001)], namely, 4003 and 7834 cm(-1), respectively. The three band systems located at 18 611, 20 700, and 22 520 cm(-1) observed by Brugh et al. [J. Chem. Phy. 109, 7851 (1998)] were attributed to the excited 11 (3)Sigma(-), 14 (3)Pi, and 15 (1)Pi states respectively. At the MRCISD level, these states are 17 560, 20 836, and 20 952 cm(-1) above the ground state respectively. We have also identified a (3)Pi state lying 14 309 cm(-1) above the ground state. The ground states of the molecular ions are predicted to be (4)Sigma(-) and (2)Delta for MoC(-) and MoC(+), respectively.
    The Journal of Chemical Physics 08/2006; 125(2):24306. · 3.12 Impact Factor
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    Pablo A Denis, K Balasubramanian
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    ABSTRACT: The potential energy curves and spectroscopic constants of the ground and 32 low-lying electronic states of ZrC have been studied by employing multireference configuration interaction methods, in conjunction with relativistic effective core potentials and 5s3p3d1f, 3s3p1d basis sets con Zr and C, respectively. We have determined that the ground state is (3)Sigma(+). However there are two low-lying (1)Sigma(+) states (below 5000 cm(-1)) which strongly interact resulting in avoided crossings. The lowest (1)Sigma(+) state corresponds to a combination of 1sigma(2) Xsigma(2) 1pi(4) configurations whereas the second is an open shell singlet 1sigma(2) 2sigma(1) 3sigma(1) 1pi(4). Several avoided crossings were observed, for (1)Pi, (3)Pi, (1)Delta, (3)Sigma(+), and (3)Delta states. We have identified (3)Pi and (1)Pi lying at 4367 and 5797 cm(-1), respectively. The results are in good agreement with the recent experimental findings of Rixon et al. [J. Mol. Spectrosc. 228, 554 (2004)], and indicate that the (3)Pi-(3)Sigma(+), and (1)Pi-(1)Sigma(+), bands located between 16 000-19 000 cm(-1) are extremely complex due to near degeneracy of several (1)Pi and (3)Pi states. We also have identified a (1)Sigma(+) state in the same region that may interfere with the (1)Pi emission bands. The present results not only shed further light into the spectra of ZrC but also predict yet to be observed systems.
    The Journal of Chemical Physics 06/2006; 124(17):174312. · 3.12 Impact Factor

Publication Stats

2k Citations
648.12 Total Impact Points

Institutions

  • 2001–2010
    • University of California, Berkeley
      • • Lawrence Berkeley Laboratory
      • • Department of Chemistry
      • • Department of Molecular and Cell Biology
      Berkeley, California, United States
    • Wroclaw University of Technology
      • Department of Physical and Theoretical Chemistry
      Wrocław, Lower Silesian Voivodeship, Poland
  • 1991–2010
    • CSU Mentor
      • • Department of Chemistry and Biochemistry
      • • Department of Mathematical & Computer Sciences
      • • Department of Chemistry
      Long Beach, California, United States
  • 1980–2010
    • Johns Hopkins University
      • Department of Chemistry
      Baltimore, Maryland, United States
  • 2003–2007
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 2001–2006
    • University of California, Davis
      • • Institute for Data Analysis and Visualization (IDAV)
      • • College of Engineering
      Davis, CA, United States
  • 2002
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 1984–2001
    • Arizona State University
      • Department of Chemistry and Biochemistry
      Phoenix, Arizona, United States
  • 1989
    • Ochanomizu University
      Tōkyō, Japan