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  • 1. AHLSTROM, M
    et al.
    JONSSON, B
    KARLSTROM, G
    ABINITIO MOLECULAR-ORBITAL CALCULATIONS ON HYDROGEN-BONDED AND NON-HYDROGEN-BONDED COMPLEXES - H2CO.H2O AND H2CO.H2S1979In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 38, p. 1051-1059Article in journal (Refereed)
  • 2.
    Ai, Yue-Jie
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Role of non-Condon vibronic coupling and conformation change on two-photon absorption spectra of green fluorescent protein2013In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 111, no 9-11, p. 1316-1321Article in journal (Refereed)
    Abstract [en]

    Two-photon absorption spectra of green fluorescent proteins (GFPs) often show a blue-shift band compared to their conventional one-photon absorption spectra, which is an intriguing feature that has not been well understood. We present here a systematic study on one- and two-photon spectra of GFP chromophore by means of the density functional response theory and complete active space self-consistent field (CASSCF) methods. It shows that the popular density functional fails to provide correct vibrational progression for the spectra. The non-Condon vibronic coupling, through the localised intrinsic vibrational modes of the chromophore, is responsible for the blue-shift in the TPA spectra. The cis to trans isomerisation can be identified in high-resolution TPA spectra. Our calculations demonstrate that the high level ab initio multiconfigurational CASSCF method, rather than the conventional density functional theory is required for investigating the essential excited-state properties of the GFP chromophore.

  • 3. Aldongarov, Anuar
    et al.
    Irgibaeva, Irina
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical study on passivation of small CdS clusters2014In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 112, no 5-6, p. 674-682Article in journal (Refereed)
    Abstract [en]

    We use density functional theory quantum chemical calculations to model optical properties of small cadmium sulphide clusters in order to explore the formation of trap states and the possibility to achieve surface passivation. The addition of capping oxygen ions on the surface of the CdS quantum dots is found to passivate the single-bonded Cd atoms. Added Cu ions resulted in the formation of deep trap states for certain locations of the copper impurity, while removal of single-bonded Cd atoms by adding S or SH groups leads to a band gap increase.

  • 4. Bondarchuk, Sergey V.
    et al.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky Cherkasy Natl Univ, Ukraine.
    DFT design of polyguanidine - a unique two-dimensional material with high-energy density2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, no 19, p. 2423-2430Article in journal (Refereed)
    Abstract [en]

    We report herein a theoretical prediction and characterisation of a new two-dimensional (2D) material based on energetic polyguanidine. The structure represents a hexagonal type lattice of the P6/m space group. The material is dynamically and mechanically stable. Highly accurate band structure calculation with hybrid functional HSE06 reveals a tiny direct band gap being equal to 0.181 eV. We provide an additional spectral characterisation of the 2D polyguanidine substance including UV-vis, nuclear magnetic resonance and nuclear quadrupolar resonance parameters. The electron transport properties of a 26.6 angstrom wide polyguanidine ribbon are calculated in terms of tight-binding density functional theory approach. The predicted 2D material is also analysed by means of Quantum Theory of Atoms in Molecules and the aromatic character of the formed rings is estimated using nucleus-independent chemical shifts quantities.

  • 5. Fahleson, T.
    et al.
    Kauczor, J.
    Norman, P.
    Coriani, S.
    The magnetic circular dichroism spectrum of the C 60 fullerene2013In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 111, no 9-11, p. 1401-1404Article in journal (Refereed)
    Abstract [en]

    The magnetic circular dichroism spectrum of the C60 fullerene has been determined with the use of Kohn-Sham density functional theory in conjunction with the CAM-B3LYP exchange-correlation functional. The experimental spectrum of Gasyna et al. [Chem. Phys. Lett. 183, 283 (1991)] covering the wavelength region above 200 nm is explained by the signal responses from the three lowest singlet states of T 1u symmetry. © 2013 Copyright Taylor and Francis Group, LLC.

  • 6. Karaush, Nataliya N.
    et al.
    Baryshnikov, Gleb V.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaeva, Valentina A.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Recent progress in quantum chemistry of hetero[8]circulenes2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, no 17-18, p. 2218-2230Article in journal (Refereed)
    Abstract [en]

    This mini-review presents recent advances in theory of electronic and spectral properties of hetero[8]circulenes used as promising fluorescent emitters for organic light-emitting diodes. Special attention is paid to the possibility of their further functionalisation into one-dimensional and two-dimensional (2D) materials. Such materials are predicted to be useful ambipolar organic semiconductors showing high charge carrier mobility. The porous structure of hetero[8]circulene-based nano-arrays can also provide suitable hydrogen storage materials, biomimetic-type nanopores and ionic channels. They serve as a good example of the density functional theory application for design of stable 2D structures, which extends the family of graphene-like materials. [GRAPHICS] .

  • 7. Lind, P.
    et al.
    Carlsson, M.
    Eliasson, B.
    Glimsdal, E.
    Lindgren, M.
    Lopes, C.
    Boman, L.
    Norman, P.
    A theoretical and experimental study of non-linear absorption properties of substituted 2,5-di-(phenylethynyl)thiophenes and structurally related compounds2009In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 107, no 7, p. 629-641Article in journal (Refereed)
    Abstract [en]

    Photo-physical properties relevant for optical power limiting in the near-visible and visible regions of the spectrum are reported for a series of substituted diarylalkynyl chalcogenophenes (furans, thiophenes, selenophenes, and tellurophenes). The linear ground and excited state absorption as well as the nonlinear (two-photon) absorption were determined at the time-dependent density functional theory level with use of the hybrid exchange-correlation functionals B3LYP and CAM-B3LYP. A selected number of the theoretically studied molecules were synthesized and characterized experimentally with the use of absorption and luminescence spectroscopy. The photo-physical data are compared to the results from optical power limiting measurements performed in THF solution at a wavelength of 532 nm, with a laser pulse length of 5 ns and pulse energies up to 150 J. The best compounds in the present investigation display an energy damping by approximately a factor of 10 at a concentration of 0.010 M.

  • 8. List, N. H.
    et al.
    Saue, T.
    Norman, Patrick
    Rotationally averaged linear absorption spectra beyond the electric-dipole approximation2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, p. 63-74Article in journal (Refereed)
    Abstract [en]

    Based on the recently developed implementation of the full semi-classical field–matter interaction operator, we present a numerically accurate yet efficient scheme to perform rotational averaging of linear absorption spectra beyond the electric-dipole approximation. This allows for a gauge-origin independent determination of UV/vis and X-ray absorption spectra for randomly oriented systems such as multilayers, liquids, and gas phase samples. The approach is illustrated by the determination of spectral intensities of electric-dipole allowed π → π* transitions and electric-dipole forbidden n → π* transitions in the UV–vis region of the spectrum as well as electric-dipole forbidden 1s → 3d transitions in the X-ray region of the spectrum. The employed Lebedev quadrature scheme shows very fast convergence with respect to the number of symmetry-independent quadrature points – in all considered cases, the oscillator strengths for the randomly oriented systems are fully converged with use of only seven quadrature points. © 2016 Informa UK Limited, trading as Taylor & Francis Group

  • 9. Luo, Y.
    et al.
    Norman, P.
    Jonsson, D.
    Ågren, H.
    Ground- and excited-state hyperpolarizabilities of cis-, trans- and diphenyl-polyenes1996In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 89, no 5, p. 1409-1421Article in journal (Refereed)
    Abstract [en]

    Calculations of ground- and excited-state polarizabilities and hyperpolarizabilities of cis-, trans- and diphenyl-polyenes have been carried out by means of cubic response theory implemented at the random-phase approximation level. The length, frequency and conformational dependences of these quantities are predicted and discussed.

  • 10. Minaev, B.
    et al.
    Loboda, O.
    Rinkevicius, Zilvinas
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Fine and hyperfine structure in three low-lying (3)Sigma(+) states of molecular hydrogen2003In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 101, no 15, p. 2335-2346Article in journal (Refereed)
    Abstract [en]

    The fine structure constant (electron spin-spin coupling) and the hyperfine structure parameters (electron-nuclear spin coupling, including spin-rotation and electron-nuclear quadrupole coupling) in the low-lying triplet states b (3)Sigma(u)(+), a (3)Sigma(g)(+) and e (3)Sigma(u)(+) of molecular hydrogen and deuterium are calculated using a recently developed technique with full configu-ration interaction and multiconfiguration self-consistent field wave functions. The second-order spin-orbit coupling contribution to the (3)Sigma(+) states splitting is negligible, and the calculations therefore provide a good estimate of the zero-field splitting based only on the electron spin-spin coupling values. For the bound state a (3)Sigma(g)(+) negligible zero-field splitting is found, in qualitative agreement with the e-a spectrum. The zero-field splitting parameter is considerable for the repulsive b (3)Sigma(u)(+) state (similar or equal to1 cm(-1) ) and of intermediate size for the bound e (3)Sigma(u)(+) state. The isotropic hyperfine coupling constant is very large not only for the valence b (3)Sigma(u)(+) state (1580 MHz) but also for the Rydberg a and e triplet states (similar or equal to1400 MHz). The quadrupole coupling constants for the deuterium isotopes are negligible (0.04-0.07 MHz) for all studied triplet states. The electric dipole activity of the spin sublevels in the triplet-singlet transitions to the ground state is estimated by means of the quadratic response technique.

  • 11.
    Minaev, Boris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Tunell, Ingvar
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Loboda, Oleksandr
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Singlet-triplet transitions in three-atomic molecules studied by time-dependent MCSCF and density functional theory2004In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 102, no 13, p. 1391-1406Article in journal (Refereed)
    Abstract [en]

    Singlet-triplet transition moments and phosphorescence lifetimes have been calculated for the three-atomic molecules HCN, O-3, H2O, H2S, GeF2, GeCl2 and GeBr2 by time-dependent density functional theory (DFT) utilizing quadratic response functions in order to qualify DFT which recently has become available for studies of this kind [TUNELL, I., RINKEVIVIUS, Z., VAHTRAS, O., SALEK, P., HELGAKER, T., and AGREN, H., 2003, J. chem. phys., 119, 11024]. Comparison with ab initio and experimental data indicates that DFT exhibit results of similar quality as explicitly correlated methods which indicates that it indeed is a viable approach for singlet-triplet transitions. O-3 provides an intriguing example in that a systematic investigation of the singlet-triplet transition moment of its Wulf band indicates a clear advantage of the DFT technique despite the multiconfigurational character of the electronic structure of this molecule. The electronic spin-spin coupling and the hyperfine nuclear coupling constants have also been calculated in order to further characterize the triplet state in the spectra of the investigated systems.

  • 12.
    Mohammed, Abdelsalam
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ringholm, Magnus
    Thorvaldsen, Andreas J.
    Ruud, Kenneth
    Hyper Raman spectra calculated in a time-dependent Hartree-Fock method2012In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 110, no 19-20, p. 2315-2320Article in journal (Refereed)
    Abstract [en]

    Hyper Raman scattering (HRS) of the benzonitrile (BN) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) molecules is studied by means of ab initio calculations. The computational procedure employs a recently developed methodology for the analytic calculations of frequency-dependent polarizability gradients of arbitrary order, including perturbation dependent basis sets. The result are compared to normal Raman scattering (NRS) and coherent anti-Stokes Raman scattering (CARS) that previously have been studied using the same technology. It is found that some suppressed or silent modes in CARS and NRS spectra are clearly seen in HRS, and that although under general excitation conditions the HRS intensities are much lower than for CARS and NRS, HRS provides complementary information useful for target identification.

  • 13.
    Natarajan Arul, Murgan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jha, Prakash Chandra
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Pressure dependence of crystal structure and molecular packing in anthracene2009In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 107, no 16, p. 1689-1695Article in journal (Refereed)
    Abstract [en]

    Anthracene molecular crystal has been investigated up to a pressure of 10.5 GPa at room temperature using variable shape variable size Monte Carlo simulations in an isothermal-isobaric ensemble. We have reported various structural quantities, such as cell parameters and unit cell volume, as a function of pressure and compared them with the experimental results [J. Chem. Phys. 119, 1078 (2003)]. The pressure dependence of angles , and which describe the relative packing of molecules in the crystal has been calculated. We report that anthracene molecular crystal does not exhibit any first order phase transition up to a pressure of 10.5 GPa which is consistent with the experimental observations by Oehzelt et al. [Phys. Rev. B 66, 174104 (2002)]. The calculated equation of state (EOS) has been fitted to a Murnaghan-type EOS with good agreement. The calculated bulk modulus and the pressure derivative of bulk modulus are 8.2 GPa and 8.9 respectively which are in agreement with the experimentally calculated values.

  • 14. Nørby, M. S.
    et al.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden .
    Kongsted, J.
    Assessing frequency-dependent site polarisabilities in linear response polarisable embedding2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, p. 39-47Article in journal (Refereed)
    Abstract [en]

    In this paper, we discuss the impact of using a frequency-dependent embedding potential in quantum chemical embedding calculations of response properties. We show that the introduction of a frequency-dependent embedding potential leads to further model complications upon solving the central equations defining specific molecular properties. On the other hand, we also show from a numerical point of view that the consequences of using such a frequency-dependent embedding potential is almost negligible. Thus, for the kind of systems and processes studied in this paper the general recommendation is to use frequency-independent embedding potentials since this leads to less complicated model issues. However, larger effects are expected if the absorption bands of the environment are closer to that of the region treated using quantum mechanics.

  • 15. Oprea, Corneliu I.
    et al.
    Frecus, Bogdan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Girtu, Mihai A.
    DFT study of electronic structure and optical properties of some Ru- and Rh-based complexes for dye-sensitized solar cells2011In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 109, no 21, p. 2511-2523Article in journal (Refereed)
    Abstract [en]

    The paper reports Time Dependent Density Functional Theory (TD DFT) calculations providing the structure, electronic properties and spectra of [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) and [Rh(III)(bpy)(3-n)(dcbpy)(n)](3+) complexes, where bpy = 2,2'-bipyridyl, dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl, and n = 0, 1, 2, 3, studied as possible pigments for dye-sensitized solar cells. The role of the metallic ion and of the COOH groups on the optical properties of these complexes are compared and contrasted and their relevance as dyes for hybrid organic-inorganic photovoltaic cells is discussed. It was found that the optical spectra are strongly influenced by the metallic ion, with visible absorption bands for the Ru(II) complexes and only ultraviolet bands for the Rh(III) complexes. Upon excitation, the extra positive charge of the Rh(3+) centre tends to draw electrons towards the metal ion, facilitating some charge transfer from the ligand to the metal, whereas in the case of the Ru(2+) ion the electron transfer is clearly from the metal to the ligand. The carboxyl groups play an important role in strengthening the absorption bands in solution in the visible region. Of the complexes studied, the most suited as pigments for dye-sensitized solar cells are the [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) complexes with n = 1 and 2. This is based on the following arguments: (i) their intense absorption band in the visible region, (ii) the presence of the anchoring groups allowing the bonding to the TiO(2) substrate and the charge transfer, and (iii) the good energy level alignment with the conduction band edge of the semiconducting substrate and the redox level of the electrolyte.

  • 16. Oprea, Corneliu I.
    et al.
    Panait, Petre
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cimpoesu, Fanica
    Ferbinteanu, Marilena
    Girtu, Mihai A.
    Comparative computational IR, Raman and phosphorescence study of Ru- and Rh-based complexes2013In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 111, no 9-11, p. 1526-1538Article in journal (Refereed)
    Abstract [en]

    We report density functional theory (DFT) calculations providing the infrared and Raman spectra of [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) and [Rh(III)(bpy)(3-n)(dcbpy)(n)](3+) complexes, where bpy = 2,2-bipyridyl, dcbpy = 4,4-dicarboxy-2,2-bipyridyl, and n = 0, 1, 2, 3, studied in the context of dye-sensitised solar cells. We compare and contrast the role of the metallic ion and of the COOH groups on the vibration and phosphorescence properties of these complexes. The vibrational spectra are not very sensitive to the replacement of the metal ion, but the presence of carboxyl groups leads to a richer spectrum due to the additional bands caused by the COOH groups. Comparison with the limited experimental data available allowed the assignment of the Raman bands. The calculated phosphorescence lifetimes suffer only modest changes when the COOH groups are introduced but vary significantly when changing the metal ion, being two orders of magnitude larger for Rh(III) than for the Ru(II) complexes.

  • 17.
    Rubio Pons, Oscar
    et al.
    KTH, Superseded Departments, Biotechnology.
    Loboda, Oleksandr
    KTH, Superseded Departments, Biotechnology.
    Minaev, Boris
    KTH, Superseded Departments, Biotechnology.
    Schimmelpfennig, Bernd
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    CASSCF calculations of triplet-state properties: Applications to benzene derivatives2003In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 101, no 13, p. 2103-2114Article in journal (Refereed)
    Abstract [en]

    We illustrate the capability of the complete active space self-consistent field method by Roos and co-workers for calculations of triplet state properties. We report phosphorescence lifetimes, zero-field splitting parameters, and nuclear quadrupole coupling constants for the lowest triplet state of a variety of benzene derivatives.

  • 18.
    Salek, Pawel
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Helgaker, T.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Jonsson, D.
    Gauss, J.
    A comparison of density-functional-theory and coupled-cluster frequency-dependent polarizabilities and hyperpolarizabilities2005In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 103, no 2-3, p. 439-450Article in journal (Refereed)
    Abstract [en]

    The frequency-dependent polarizabilities and hyperpolarizabilities of HF, CO, H2O and para-nitroaniline calculated by density-functional theory are compared with accurate coupled-cluster results. Whereas the local-density approximation and the generalized gradient approximation (BLYP) perform very similarly and overestimate polarizabilities and, in particular, the hyperpolarizabilities, hybrid density-functional theory (B3LYP) performs better and produces results similar to those obtained by coupled-cluster singles-and-doubles theory. Comparisons are also made for singlet excitation energies, calculated using linear response theory.

  • 19. Sulzer, D.
    et al.
    Norman, Patrick
    Linköping University, Sweden.
    Saue, T.
    Atomic C 6 dispersion coefficients: A four-component relativistic Kohn-Sham study2012In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 110, no 19-20, p. 2535-2541Article in journal (Refereed)
    Abstract [en]

    We present C 6 homo- and heteroatomic dispersion coefficients for all closed-shell atoms of the periodic table based on dipole-dipole polarizabilities at imaginary frequencies calculated using our recent extension of the complex polarization propagator approach to the four-component relativistic Kohn-Sham approach. Lack of proper reference data bars definite conclusions as to which density functional shows the overall best performance, and we therefore call for state-of-the-art wave function-based correlated calculations of dispersion coefficients. Scalar relativistic effects are significant already for elements as light as zinc, whereas spin-orbit effects must be taken into account only for very heavy elements.

  • 20.
    Valiev, Rashid R.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Eland, J. H. D.
    Feifel, R.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Optimization of core–valence states of molecules2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, no 1-2, p. 252-259Article in journal (Refereed)
    Abstract [en]

    Core–valence double-electron ionisation spectra of a few small molecules–carbon monoxide, ammonia, methyl fluoride and thiophene–are presented and analysed using the self-consistent field algorithm introduced by Hans Jørgen Jensen 30 years ago. It confirms the utility of this algorithm, frequently employed to obtain stable and sharp convergence of wave functions for the benefit of calculations of a great variety of molecular properties, thus also for optimisation of core–valence states and for the interpretation of the corresponding spectra.

  • 21.
    Vieitez, Maria Ofelia
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Ivanov, T. I.
    Sprengers, J. P.
    de Langey, C. A.
    Ubachs, W.
    Lewis, B. R.
    Stark, G.
    Quantum-interference effects in the o(1)Pi(u)(v=1)similar to b(1)Pi(u)(v=9) Rydberg-valence complex of molecular nitrogen2007In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 105, no 11-12, p. 1543-1557Article in journal (Refereed)
    Abstract [en]

    Two distinct high-resolution experimental techniques, 1 XUV + 1 ' UV laser-based ionization spectroscopy and synchrotron-based XUV photoabsorption spectroscopy, have been used to study the o(1) Pi(u)(v =) 1 similar to b(1)Pi(u)(v=9) Rydberg-valence complex of N-14(2), providing new and detailed information on the perturbed rotational structures, oscillator strengths, and predissociation linewidths. Ionization spectra probing the b '(1)Sigma(+)(u)(v= 6)state of N-14(2), which crosses o(1)Pi(u)(v=1) between J = 24 and J = 25, and the o(1)Pi(u)(v= 1), b(1)Pi(u)(v= 9), and b '(1)Sigma(+)(u)(v= 6) states of (NN)-N-14-N-15, have also been recorded. In the case of N-14(2), rotational and deperturbation analyses correct previous misassignments for the low-J levels of o(v=1) and b(v= 9). In addition, a two-level quantum-mechanical interference effect has been found between the o-X(1, 0) and b-X(9, 0) transition amplitudes which is totally destructive for the lower-energy levels just above the level crossing, making it impossible to observe transitions to b(v=9, J=6). A similar interference effect is found to affect the o(v=1) and b(v=9) predissociation linewidths, but, in this case, a small non-interfering component of the b(v= 9) linewidth is indicated, attributed to an additional spin - orbit predissociation by the repulsive 3(3)Sigma(+)(u) state.

  • 22. Wang, Zhao
    et al.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Hard-sphere fluid mediated interaction: a pressure expression with application of the weighted correlation approach2016In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 114, no 5, p. 599-607Article in journal (Refereed)
    Abstract [en]

    By using a so-called differential-integral method on the chemical potential of a hard-sphere fluid, a special variant of our previously developed expression that describes the interaction between charged plates immersed in an electrolyte, is introduced to examine the hard-sphere fluid mediated pressure in a slit. The resulting expression consists of a kinetic contribution and a hard-sphere contribution, and it is formulated as a function of the single-particle direct correlation function and the density distribution of a hard-sphere fluid. It allows us to conveniently apply the classic density functional theory to explicitly investigate the influence of the hard-sphere excluded-volume effect on the interaction pressure between surfaces. In this study, a newly proposed weighted correlation approach (WCA)-Denton and Ashcroft (DA) method is employed to predict the interaction pressure as well as its pressure components for a hard-sphere fluid inside a slit pore. Comparisons with the results from the Monte Carlo simulations and the fundamental measure theory suggest that the WCA-DA method is able to accurately capture the detailed characteristic pattern of the pressure-separation curves at different fluid densities. It is also found, both qualitatively and quantitatively, that the hard-sphere pressure contribution dominates over the kinetic pressure contribution in determining the oscillatory behaviour of the interaction pressure curves, especially when a hard-sphere fluid of high density is concerned.

  • 23. Wörmke, Stephan
    et al.
    Brendel, K.
    Andresen, U.
    Mader, H.
    A molecular beam Fourier transform microwave study of 2-methylpyridine and its complex with argon: structure, methyl internal rotation and N-14 nuclear quadrupole coupling2004In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 102, no 14-15, p. 1625-1639Article in journal (Refereed)
    Abstract [en]

    The rotational spectrum of 2-methylpyridine (alpha-picoline, CH3C5H4N) in the two lowest levels of methyl internal rotation (m = 0, +/-1) has been recorded in the frequency range from 2 to 15 GHz using a molecular beam Fourier transform microwave spectrometer. The high resolution and sensitivity of this spectroscopic technique allowed resolution of hyperfine structures due to N-14 nuclear quadrupole coupling with high accuracy and detection of the spectra of the N-15- and all C-13-isotopomers. These investigations considerably extend the results from an earlier study on the normal species (DREIZLER, H., RUDOLPH, H. D., and MADER, H., 1970, Z. Naturforsch., 25a, 25); improved rotational and centrifugal distortion constants as well as all components of the N-14 quadrupole coupling tensor have been obtained. Analysis of the spectra of the isotopomers yielded the N-14 quadrupole coupling constants X,c and chi(aa) - chi(bb) (for the C-13 species), the potential parameter V-3 for the barrier hindering the internal rotation of the methyl group, and, in particular, r(o), r(s), r(m)((1)) and r(m)((2)) structural parameters for the molecule. In addition to the microwave studies on the monomer, we have also investigated the rotational spectrum of the weakly bound dimer of normal 2-methylpyridine with Ar. The results obtained for the quadrupole coupling constants and the hindering potential for the internal methyl rotation show that the corresponding parameters are not significantly, or only slightly, changed in the complex.

  • 24. Zhaunerchyk, V.
    et al.
    Hellberg, F.
    Ehlerding, A.
    Geppert, W. D.
    Larsson, M.
    Vane, C. R.
    Bannister, M. E.
    Bahati, E. M.
    Österdahl, Fabian
    KTH, School of Engineering Sciences (SCI), Physics.
    af Ugglas, M.
    Thomas, R. D.
    Dissociative recombination study of PD2+ at CRYRING: absolute cross-section, chemical branching ratios and three-body fragmentation dynamics2005In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 103, no 20, p. 2735-2745Article in journal (Refereed)
    Abstract [en]

    The paper reports an investigation of the dissociative recombination of PD2+ at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ranging from 1 meV to 0.1 eV. The experiment performed has shown the dissociative recombination of PD2+ to be dominated by three-body break-up, with a branching ratio of about 78%. Competition between the available three-body channels producing the ground state, P(S-4), and the. first two excited states, P(D-2) and P(P-2), is observed. The formation of the first excited state dominates over the other two almost equally probable channels with about 75% of all three-body events. The results indicate that the kinetic energy released in the three-body break- up of PD2+ is randomly shared between the deuterium atoms. The intra-molecular angle on dissociation has also been investigated. A comparative analysis of the dissociative recombination dynamics for the two isovalent systems, PD2+ and NH2+, is undertaken.

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